PHYSICAL Metallugy of Titanium by I.I. Kornilov

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PHYSICAL METALLURGY OF TITANIUM

1. I. Kmilau. Ed& in Chief

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WATIOWAL AEROHAUTICS AND SPACE ADMlHlSTRAflOH * WASHiH6TOU, I). f. NOVEMBER 1965

NASA T T F-338

PHYSICAL METALLURGY OF TITANIUM

I. I. Kornilov, Edi tor in Chief

Works of the Fifth Conference on Metallurgy, Physical Metallurgy, and Application of Titanium and Its Alloys

March 1963

A. A. Baykov Institute of Metallurgy

Izdatell s tvo Nauka Moscow, 1964

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

For sale by the Clearinghouse for Federal Scientific and Technical Information Springfield, Virginia 22151 - Price$7.00

TABLE OF CONTENTS

Page -

PREFACE vi

PART I. METAL CHEMISTHY OF T1TAIVIU.M ALGOYS 1

Prospects for the Development of Investigations of the Heat Resistance of Titanium Alloys 1

Phase Diagram of the System Ti-O2 and Some Properties of the Alloys of This System

Equilibrium Diagram of the Quarternary System Ti-Al-Mo-V 29

Phase Structure of Alloys of the System Ti-Al-Fe-Cr-Si with a Constant Content of Aluminum and Silicon 35 Study of the Alloys of the Ternary System Ti-Al-Zr 46

Phase Equilibrium of Alloys of the Section Ti3Al-Zr of the Ternary System Ti-Al-Zr 53

Study of the Phase Structure of the Alloys of the System Ti-Al-Zr Along the Section Ti3Al-Zr 58 Relationship of Structures Formed on Quenching Titanium Alloys to Equilibrium Phase Diagrams 67 Stability of ,!3 Alloys of the System Ti-Mo-Cr-Fe-Al

Metastable Polymorphism of Alloys Based on Elements of Group IV of the Periodic System 90

Dilatometric Study of Transformations in Titanium Alloys 99 Dislocation Theory of the Hydrogen Brittleness of Titanium Alloys 110

Effect of Alloying on the Physicochemical Properties of Titanium

Determination of the Characteristics of the Interdiffusion of Titanium and Molybdenum From the Attenuation of y Radiation 137

PART 11. INTERACTION OF TITANIUM WITH GASES AND TRE CORROSION PROPERTIES OF ALLOYS

On the Redis t r ibut ion of Impuri t ies i n Titanium and I t s Alloys During Oxidation

Effec t of Oxygen on the Mechanical P roper t i e s of Heat- Treated Alloys AT3 and AT^

Charac te r i s t i c s of the Oxidation of Cer ta in Titanium Alloys During Heating P r i o r t o P l a s t i c Deformation

Ni t r id ing of Titanium Alloys a t High Pressures

Corrosion of Titanium Alloys of Se r i e s VT and AT i n Solu- t i o n s of Su l fu r i c Acid Containing Nickel Su l fa te

Chemical S t a b i l i t y of Titanium i n Certain Aggressive Media and Scope of I ts Use i n Chemical I n d u s t r i a l Equipment

Chemical S t a b i l i t y of Titanium i n Hydrohalic Acids and Halogens

Ef fec t of Sodium N i t r i t e on the Corrosion of Titanium by Hydrochloric and Su l fu r i c Acid

Study of the Use of Titanium Alloys i n t h e Construction of Food Machines

PART 111. MECmICAL AND TECRNOLOGICAL PROPERTIES OF TITANIUM ALLOYS

Basic Prerequis i tes f o r Developing High-Strength Titanium Alloys With an a + @-Structure by Means of Alloying and Heat Treat ing

Strength of Interatomic Bonding of Single-Phase Alloys i n the System Ti-Nb-Cr

Study of the Creep of Alloys i n the System Ti-V-Nb-Mo

Character is t ics of t h e Cold B r i t t l e n e s s of Titanium

Creep of Alloy -4T3 a t 350'

Study of the Creep and Thermal S t a b i l i t y of Alloy AT& a t 500

Determination of t h e Relaxa$ion Resistance of Alloy AT3

Creep of Alloys of t h e Quaternary System Ti-Zr-Al-Sn a t 750'

Page

Study of the Mechanical Proper t ies of Titanium Alloys AT3, AT^, AT^ and AT^ i n Relat ion t o the Testing Temperature 276

Study of the Comparative Heat Resistance of Titanium Alloys Sheet and Its Weld J o i n t s a t 450, 550, 650 and 700 282

High-Temperature Strength of Alloys of the Quaternary System Ti-Al-Mo-V 283

Heat Resistance of Titanium Alloy AT^ i n Short-Time Tests 28 9

Thermal S t a b i l i t y of Alloys AT3 a t Temperatures of 350 and 400' 290

Ef fec t of Conditions of P l a s t i c Deformation and Subsequent Treatment on the Proper t ies of Cer ta in Titanium Alloys 297

Study of the Basic Parameters of Hot and Medium Temperature Rolling of Some Titanium Alloys Under Special Conditions o f S t r e s s 304

Some Studies of the St ructure and Proper t ies of Alloy VT5-1 During Heating f o r Stamping 305

Some Character is t ics of the Heat Treatment of Alloy AT3 With a Low Content of Alloying Elements 3x1 Some Problems of Fusion Welding of Titanium and Its Alloys 318

Submerged Double-Arc Welding of Medium and Large Thickness Semifinished Products of Titanium Alloys 319

Study of t h e Mutual Diffusion of Titanium With Copper and Other Metals Sui table f o r Brazing 3 20

Use of Optical Emission Microanalysis i n the Study of Titanium Alloys 321

Defect Inclusions i n Titanium Ingots 33 2

Metastable Phases of Titanium Alloys and Conditions of Their Formation 3 40

PREFACE

The holding of annual scientific and technical conferences on the problem of titanium has become an established tradition. At such conferences, the results of research done by many scientific institutions and enterprises on various aspects of this problem during the preceding year are presented, and plans are drawn up for the further development of research and experimental industrial work on titanium and its alloys.

The present collection includes the works of the Fifth Scientific Confer- ence, held in Moscow in March, 1963.

The section "Metal Chemistry of Titanium Alloys" offers the results of a further development in research on the chemical interaction between titanium and the major elements of the periodic system in simple and multicomponent systems, and presents phase diagrams with titanium as the main component that are of great scientific and practical interest.

Of particular importance are the results of research on the interaction of titanium and its alloys with gaseous admixtures, particularly oxygen, nitrogen, and hydrogen, and on the influence of these admixtures on the physical and mechanical properties of the alloys described in the second section of the collection. This section also provides data on the chemical stability and corrosion resistance of titanium and some of its alloys in various corrosive

The physical and mechanical properties of the alloys, the results of studies of the creep and relaxation resistance and comparative high-temperature strength of experimental industrial and mass produced alloys are comprehensively discussed in the third section of the collection.

The present collection constitutes evidence of the further progress made in the research on processes and phenomena taking place in titanium alloys under various conditions of industrial production and application, and directs the scientific and engineering thought toward the establishment of new goals in the problem of titanium and its alloys.

It is hoped that the publication of the present collection will be met with interest by the scientists, engineers, and technicians of the country and will foster further progress in the scientific investigation, production and extensive introduction of titanium and its alloys into various branches of modern technology.

I. I. Kornilov

PART I. METAL CIiEMTSTRY OF TITANIUM ALLOYS

PROSPECTS FOR TRE DEVELOPMEXI' OF INVESTIGATIONS OF THE REAT IIESISTANCE OF TITANIUM ALLOYS

I. I. Kornilov

The problem of development of inves t igat ions i n t o t h e heat r e s i s t ance of t i tanium a l loys has not been extensively t r e a t e d i n the l i t e r a t u r e . The s t a t e - ments of c e r t a i n authors t o t h e e f f e c t t h a t on t h e bas i s of ca lcu la t ions of t h e d i f fus iona l mobil i ty of t i tanium atoms it i s d i f f i c u l t t o expect a r i s e i n t h e t e pera ture l i m i t of the high-temperature s t r eng th of t i tanium a l loys above 4&-450 a r e incor rec t and have not been confirmed i n pract ice . I n i t s pure fdrm, t i tanium displays creep even a t room temperature, and t h i s creep increases with r i s i n g temperature.

There a r e some r e a l p o s s i b i l i t i e s of subs tan t i a l ly increasing t h e high re- s i s t ance of titanium. They p e r t a i n t o the physicochemical f a c t o r s of t h e hardening of metals. By increasing the s t r eng th of t h e chemical bond obtained by forming s o l i d solut ions and compounds of titanium, one can r a i s e the tempera- t u r e l e v e l of t h e s t rength of t i tanium. These bas ic f a c t o r s involved i n r a i s - ing t h e high-temperature s t rength of metals a re discussed i n references 1-4.

From t h e standpoint of t h e physicochemical theory of heat r e s i s t ance of metal a l loys which we formulated and developed ( r e f . 3 ) , high-temperature hardening i s determined by t h e nature of t h e chemical in te rac t ion of t h e components, the nature of t h e phases formed i n t h e system, t h e i r s t a t e , which depends on equilibrium fac to r s , and transformations i n the s o l i d s t a t e . An increase i n high-temperature s t rength i s achieved pr imar i ly a s a r e s u l t of t h e ac t ion of the so lu t ion and dispers ion mechanisms of hardening of metal a l loys ( r e f . 3) . For t h i s reason, an important aspect of t h e high-temperature s t rength of titanium a l loys i s the in te rac t ion of t i tanium with o the r elements.

On t h e bas is of t h e chemical p roper t i e s of t i tanium ( r e f s . 4 and 5 ) ) we divided a i l the elements of the per iodic system i n t o th ree main groups i n re- l a t i o n t o titanium; these elements form wi th t h e l a t t e r :

(1) continuous so l id solut ions; (2) l imi ted s o l i d solut ions with metal compounds, and (3 ) ion ic compounds.

Of all the elements of the periodic system, those which are the most important for alloying titanium and hardening its alloys at high temperatures are -

those which we classified in the first and second group. There are over 50 such elements.

According to the classification which we adopted (ref. 4)) the elements of these two groups are characterized by the following types of equilibrium diagrams :

1. Continuous solid solutions with a- and @-modifications of titanium, with. $ Z a-transformations; these include systems of titanium with its close analogues Zr and Hf.

2. Continuous solid solutions with @-Ti, very. limited solid solutions with a-Ti, and the two-phase @ + a region; these include systems of titanium with metals of transition groups located close to titanium; V, Nb, Ta, Mo and u.

3. Limited solid solutions of a- and $-Ti with a peritectoid reaction and formation of compounds; these include systems with Al, Ge, Sn, Pb, La, Ce, B, C, .O, E, etc.

4, Limited solid solutions of a- and @-Ti with a eutectoid reaction and the formation of compounds; these include systems with Cr, Mn, Fe, Co, Ni, Cu, Si, and many otbers.

All these types of interaction are reflected in the phase diagrams of these systems (ref. 6). We represented them in reference 5 in the form of gen- eralized equilibrium diagrams according to the types of interaction.

In addition to these equilibrium diagrams of binary systems, one can also distinguish, in the corresponding ternaryand more complex systems, quasi-binary and quasi-ternary systems which include systems made up of two, three or more metallic compounds of titanium. Among them, one can distinguish systems composed of iso~orphous compounds such as Ti AL-T~ Sn, Ti U-Ti In, Ti Sn-Ti In, 3 3 3 3 3 3 Tier2-TiFe2, TiCr2-ZrCr2, Ti Al-Ti Sn-Ti In, and many others. When certain 3 3 3 conditions are maintained, all these systems of metallic compounds are capable of producing solid metallic solutions or ternary compounds.

The physicochemical theory of high-temperature strength (ref. 3) and the equilibrium diagrams of the systems make it possible to determine the dependence of the high-temperature strength on the composition and structure of the alloys, and to use the derived relationships for the establishment of the scientific principles to be used in the development of new heat-resistant titanium alloys.

Let us examine some experimental data on the high-temperature strength of titanium systems. As was shown in references 7 and 8 in the Ti-Zr system at relatively low temperatures (300-400~), the high-temperature strength in the

region of continuous solid solutions based on a-Ti changes with the composition by passing through a smooth maximum; as the temperature of the cu 2 $ transformation (8600) is approached, the high-temperature strength is affected by the activated state of the atoms in the solid solution, which causes an increase in the rate of creep of the alloys. The same type of change in high-temperature strength should be expected in the Ti-Hf system.

In systems with continuous $ solid solutions limited by cu solid solutions of titanium and an intermediate two-phase cu + $ region, the high-temperature strength not only increases in the region of cu solid solutions, reaching a small maximum near the boundary of the two-phase cu + $ region; in the two-phase region, the high-temperature strength decreases considerably, and as one moves into the region of $ solid solutions and of increasing concentration of elements, the high-temperature strength increases again. We illustrated this with examples of the high- temperature strength of Ti-V and Ti-Nb systems (ref. 9). "Composition- high-temperature strength" diagrams of the systems Ti-Mo and Ti-Ta, which have not been studied experimentally, should be similar in character. Thus, in systems with continuous $ solid solutions and limited cu solid solutions, the "composition-high-temperature strength" diagrams show only one maximum near the boundary of the a 2 8 transformation, a minimum in the region of a + 8 phases, and an increase in high-temperature strength in the region of 8 solid solutions. Elements forming limited solid solutions with a peritectoid reaction have an appreciable effect on the increase in the high-temperature strength of titanium. Most effective in this respect were found to be alloys of the Ti-Al system in the region of a limited solid solutions. Here a major part is apparently played by Kurnakov-type compounds, which form in this system owing to the ordering of the structure of a solid solutions. Without considering the results of studies (refs. 5, 6, 10 and 11) on the refinement of the equilibrium diagram of the system to be definitive, one can tell that from the a solid solutions of this system are formed the compounds Ti6Al and Ti Al (ref. 11) and, according to 3 literature data (ref. 6), the compound Tim, which crystallizes from the peri- tectic reaction. The presence of these compounds is particularly manifested in the variation of the mechanical properties (ref. 12) and high-temperature strength (ref'. 13) of alloys of this system. The Ti-Sn is interesting in this respect. It also has a region of limited a solid solutions with a peritectoid reaction, and the compound Ti Sn, having a hexagonal lattice, is formed therein 3 (ref. 14). The high-temperature strength of the alloys of this system with limited a solid solutions is characterized by a maximum near the limit of maximum solubility, a maximum vaiue of the high-temperature strength of the 6 phase based on the compound Ti Sn, and a minimum of high-temperature strengt:~ in the 3 two-phase Q: + 6 region. "Composition-high-temperature strength" diagrams of this type should apply to the following analogous systems with limited solid solutions: Ti-&, Ti-Ge, Ti-In, Ti-Ga, Ti-Pb, Ti-Ce, etc.

The above-enumerated systems of limited a solid solutions of titanium and peritectoid reactions are the most promising for the development of heat- resistant titanium alloys. The high-temperature strength of systems with a low solubility of the components in a-Ti and a eutectoid reaction has been studied to a lesser extent. These systems (fig. 1) are characterized by low temperatures of the eutectoid transformation. The lowest temperature of the eutectoid

Content of element, at.percent

Figure 1. Phase diagrams of titanium systems with a eutectoid transformation. 1, Ti-Cr; 2, Ti-Mn; 3, Ti-Pe; 4, Ti-Co; 5, Ti-Ni.

transformation is found in the system Ti-Mn; the temperature of the eutectoid transformation rises as the elements of the 4th period become farther removed from Ti. On this basis, elements of the 4th period can be arranged in a series characterized by a gradual rise in the temperature of the eutectoid transformation, as follows: Mn + Fe + Cr -t Co + Ni -+ Cu. A certain deviation of Mn and Fe from the sequence of this series has thus far remained unexplained. The solubility of these metals in a-Ti (fig. 1) amounts to tenths of one percent, with the exception of copper, in which it attains 2 atomic (at.) percent. The very limited solubility of these metals in a-Ti and the eutectoid transformation determine the high-temperature strength of the alloys of similar binary systems. A low strength can be expected in the systems Ti-Mn and Ti-Fe with low temperatures of the eutectoid transformation and a gradual rise in this strength can be expected as one passes to the systems Ti-Cr, Ti-Co and Ti-Ni, since in the latter a gradual rise in the temperatures of the eutectoid transformation is observed. The highest values of the high-temperature strength can be assumed to prevail in alloys of the system Ti-Cu, both because of the high concentration of solid solutions of copper in a-Ti, and because of the maximum value of the temperature of the eutectoid transformation of this system. An additional hardening in these systems also can be caused by dispersed precipitates of the excess phase from supersaturated a solid solutions of titanium. However, no experimental data are available on the high-temperature strength of such binary systems, and the latter must be investigated independently.

Systems composed of titanium compounds with other metals are promising for increasing the high-temperature strength of titanium. One of such interesting

systems is a quasi-binary section of the ternary system Ti-Al-Sn (refs. 15 and 16) passing through the compositions of two compounds: Ti Al and Ti Sn. An

3 3 experimental study of this system showed that on the polythermal section of the alloys of these two compounds at high temperatures (fig. 2, upper part), the system is not quasi-binary and the alloys crystallize in the eutectic type. At low temperatures, below the temperature of formation of the compound Ti Al from 3 the a solid solution, the system becomes a quasi-binary one composed of two intermetallic compounds, Ti3A1-Ti Sn, Ti Al being formed from the a solid solu- 3 3 tion, and Ti Sn being formed during crystalfization. These two compounds with 3 an isomorphous hexagonal lattice form continuous solid solutions, as was shown in reference 16.

A study of the high-temperature strength of the alloys of this section as a function of Ti Sn content (by the flexural method) has shown that the strength 3 changes in accordance with the "composition-high-temperature strength" diagram of the first type. As is evident from the series of curves in the lower part of

percent J

Figure 2. Phase diagrams and composition versus high-temperature strength of alloys of the ternary system Ti-Al-Sn along the section Ti Al-Ti Sn. 3 3

f igure 2, t h e time necessary f o r the bending de f lec t ion t o reach 2, 3, 4, 5 and 7 mm passes through a smooth maximum i n t h e region of a l loys containing 40-60 percent T i Sn. The se lec ted temperatures were 700-750~, and t h e s t r esses , 3 13-25 kg/mm2. We obtained s i m i l a r r e s u l t s on the sec t ion corresponding t o com- pos i t ions of t h e compounds Ti6M-Ti Sn. 3

Taking a s the bas i s t h e compositions of the compounds Ti6M and Ti3=, by

addi t ional al loying with hardening elements, the author i n col labora t ion wi th T. T. Nartova developed new hea t - res i s t an t t i tanium a l loys based on T i 6 u com-

pounds with a working temperature up t o 700, and a l loys based on Ti3M with a

working temperature up t o 800' ( r e f s . 17 and 18). I n a study of the s t ress- rupture s t rength of a l loys based on t h e compound

Ti6& a t 700 ( f ig . 3) by t h e standard extension method, we es tabl ished t h e dependence of the time of f a i l u r e of t h e specimens on t h e given s t r e s s ( re f . 18).

Although da ta on t h e high-temperature s t rength and many o the r p roper t i e s of a l loys based on the compounds Ti6& and T i A l have thus f a r been insuf f i - 3 c ient , it i s nevertheless poss ib le t o assume t h a t c e r t a i n compositions of a l - loys based on these compounds make it possible t o a t t a i n working temperatures of 600-800~, i. e. , approximately those which correspond t o t h e temperatures of appl ica t ion of s t a i n l e s s a u s t e n i t i c s t e e l s and c e r t a i n hea t - res i s t an t n ickel a l loys . It should be emphasized t h a t the spec i f i c g rav i ty of t i tanium a l loys based on t h e compounds T i 6 a and T i Al i s almost one-half O f t h a t of s t e e l and 3 nickel a l loys . However, it should be kept i n mind t h a t t h e p l a s t i c p roper t i e s of t i tanium al loys based on these compounds w i l l be considerably lower than those of aus ten i t i c s t e e l s and nickel al loys.

The l i t e r a t u r e contains evidence on the development of highly heat- r e s i s t a n t t i tanium a l loys whose base i s t h e compound TiAl ( r e f . 1 9 ) ) a s we had a l so pointed out i n our work ( r e f . 20). Of specia l s igni f icance i s t h e group

log ~ / h r

Figure 3. Stress-rupture s t rength of t i tanium a l l o y based on the compounds Ti6A.l and of aus ten i t i c s t e e l s a t TOO0.

of alloys based on intermetallic compounds that are heat-resistant casting titanium alloys. Real prospects for the development of new heat-resisthnt titanium alloys are opening up thanks to studies of multicomponent systems. This was pointed out in connection with the development of heat-resistant titanium alloys based on a solid solutions of the system Ti-Al-Cr-Fe-Si-B (ref. 21). O f great interest in this respect are ternary, quaternary and more complex systems based on titanium. In these systems, one can distinguish alloy compositions corresponding to the region of solid solutions of a- and @-Ti, and to quasi- binary and quasi-ternary sections of intermetallic systems.

Among promising heat-resistant alloys based on the a-structure one should also distinguish such important ternary systems as Ti-Al-Sn, Ti-Al-Zr, Ti-Al-Cu, Ti-Al-Mo and many others. Among quaternary systems of this series, the following may be considered important: Ti-Al-Sn-Zr, Ti-Al-Zr-Cu, Ti-Al-Zr-Cr, Ti-A1-V-Mo, etc. 1

Let us examine the three-dimensional diagram of a part of the quaternary system Ti-IU-V-Mo (fig. 4). A wide region of a solid solutions which is adjacent to the edge of the tetrahedron is visible in this figure. In addition, in the portion of the system under study, there is a region of quaternary @ solid solutions which is of interest in a study of heat-resistant alloys based on the stable B-structure.

An example of titanium alloys with a wide region of the stable p-struct;re is the ternary system Ti-Cr-Mo, studied in reference 22. One of the isotherms (at 600) of the system (fig. 5) shows the principal phase regions in this

Figure 4. Three-dimensional diagram of a part of the quaternary system Ti-K7-Mo-V.

I The system Ti-Al-V-Mo was studied in detail by Ye. N. Pylayeva and KO Chih-ming (see this collection, pp. 26-29).

7

Cr

Mo, w t percent

90 80 70 GO 50 440 340 ZZD I40 T i , w t percent

Figure 5. Isothermal section of the ternary system Ti- Cr-Mo a t 600'.

system, including the wide region of @-ternary solid solutions. This system and other s imilar ones make it possible t o develop new heat-res is tant titanium alloys based on the s table f3-structure.

Using the da ta of Ye. N. Pylayeva and KO Chih-ming, we present a "composition-high-temperature strength" diagram of the a l loys of t he quaternary system Ti-A1-Mo-V ( f ig . 6 ) . The al loys correspond t o a r ad i a l section with 20 percent Al and a variable content of the sum V + Mo = 1:l. The same f igure shows curves characterizing the time necessary f o r a bending def lect ion of 2, 5 and 10 mm as a function of the variable content of the sum V + Mo (from 0 t o 5 percent) . The t e s t s were carried out a t 700-800' and a t a constant s t r e s s of

2 15 kg/mm . The curves show tha t the alloys of t h i s system have maximum values of high-temperature strength a t 700-800 i n the v ic in i ty of the saturat ion l i m i t of the a sol id solution.

Considering the poss ib i l i t i e s of obtaining working temperatures of 600-800' f o r cer ta in heat-resistant titanium alloys, one can compare the r a t e s of increase i n the temperature l eve l of the high-temperature strength of titanium alloys with those of nickel a l loys . The curves representing the r i s e i n the temperature leve l of high-temperature strength with the years f o r titanium alloys ( f ig . 7, lower curve) and nickel a l loys ( f ig . 7, upper curve) show t h a t i n approximately ten years (1952-1962) the temperature l eve l of the strength of titanium al loys rose from 200 t o 800, i .e . , by 600, while the temperature l eve l of nickel al loys increased i n ten years (1949-1959) from 700 t o 950, i .e . , by 250'.

This is explained by the f a c t t h a t i n titanium al loys there a r e unex- ploi ted poss ib i l i t i e s of hardening and rais ing the temperature l e v e l of the high-temperature strength. Studies i n t h i s direct ion were begun only 5-6 years

Mo + V, w t percent Figure 6. "Composition-high-temperature strength" diagram a t 700-8000 of a l loys of t h e system Ti-Al-Mo-V; sect ion with 20 percent Al a t a var iable content V:Mo = 1:l.

-.

7lUU

Gll

4ffO

1352 If54 1356 1358 years

Figure 7. Rise i n t h e temperature l e v e l of t h e s t rength of n icke l (1) and t i tanium (2) a l loys i n 1 0 years.

ago, whereas t h e high-temperature s t rength of n icke l a l loys has now been studied f o r over 15 years, and the bas ic f a c t o r s a f fec t ing t h e i r hardening have now been almost exhausted. The prospects f o r a f u r t h e r increase i n t h e temperature l e v e l of the highltemperature s t rength of t i tanium a l loys have not y e t been exhausted, and f u r t h e r systematic. inves t igat ions w i l l make it poss ib le t o r a i s e it s t i l l fu r the r .

Summary

1. The a r t i c l e has es tabl ished c e r t a i n re la t ionsh ips governing t h e dependence of t h e high-temperature s t rength of t i tanium a l loys on t h e nature of t h e in te rac t ion of t h e components with titanium, types of equilibrium diagrams of t h e systems, and s t r u c t u r e of the a l loys .

2. Experimentally obtained "composition-high-temperature strength" diagrams of certain simple and multicomponent titanium systems will make it possible to use these relationships for the development of new heat-resistant titanium alloys having optimum properties.

3. An important role in the creation of new heat-resistant titanium alloys is played by the stable structures of a and @ solid solutions and also by metallic compounds of titanium and alloys based on these compounds.

4. Promising in this respect are multicomponent a and @ solid solutions of systems based on titanium and the titanium compounds Ti6& and Ti3Al, which

are formed from a solid solutions of the system Ti-A1.

5. Alloys made from the phases enumerated above can have working temperatures up to 600-800~.

1. Bochvar, A. A. Physical Metallurgy (~etallovedeniye). Metallurgizdat, (State Scientific and Technical Publishing House for Literature on Ferrous and Nonferrous ~etallurgy), pp. 287-297, 1956.

2. Osipov, K. A. Problems of the Theory and High-Temperature Strength of Metals and Alloys (voprosy teorii zharoprochnosti metallov i splavov) . IZ~-vo AN SSSR, 1960.

3. Kornilov, I. I. Physicochemical Principles of the Aigh-Temperature Strength of Alloys (Fiziko-khimicheskiye osnovy zharoprochnosti splavov ) . IZ~-vo AN ,SSSR, 1961.

4. --- Izv, &!4 SSSR, OKhN, Mo. 4, p. 395, 1957.

5. --- Coll. '%tanium and Its Alloys" (Sb. "Titan i y e p ~~lax&"), No. 7, p. 5 , NO. 10, p. 10, 1963.'

Hansen, M. and Anderko, K. Structures of Binary Alloys (~truktury dvoynykh splavov) . Metallurgizdat, 1962.

Glazova, V. V, and Kurnakov, N. N. Izv. AN SSSR, OTN, Metallurgiya i Toplivo, No. 3, p. 67, 1961.

Grigorovich, V. K. and Safonov, Yu. S. Izv. AN SSSR, OTN, Metallurgiya i Toplivo, No. 5 , p. 38, 1960.

Kornilov, I. I. and Vlasov, V. S. Izv. AN SSSR, OTN, Metallurgiya i Toplivo, No. 4, p. 31, 1958.

10. Ence, E. and Anderko, K. Trans. AIME, Vol. El, No. 1, p. 151, 1961.

11. Grum-Grzhimaylo, N. V., Kornilov, I. I., Pylayeva, Ye. N. and Volkova, M.A. ~ o k l . AN SSSR, Vol. 137, No. 3, p. 599, 1961.

12. Moiseyev, V. N. Metallovedeniye i termieheskaya obrabotka metallov, No. 6 , p. 30, 1960.

13. Kornilov, I. I., Pylayeva, Ye. N. and Volkova, M. A. Izv. AN SSSR, O W , No. 7, P. 771, 1956.

14. Kornilov, I. I. and Nartova, T. T. Zhurnal neorganicheskoy khimii, Vol. 5, NO. 3, p. 662, 1960.

--- ~ o k l . AN SSSR, V O ~ . 131, NO. 4, p. 837, 1960.

--- ~ o k l . AN SSSR, ~ o l . 140, NO. 4, p. 829, 1961.

--- Izv. AN SSSR, OTN, Metallurgiya 5. Toplivo, No. 6, p. 142, 1962.

- - - D O ~ X . AN SSSR, V O ~ . 1-48) NO. 3, p. 644, 1963.

Andrew, J. and Kessler, H. J. Metals, Vol. 8, No. 10, 1956.

Kornilov, I. I. Izv. AU SSSR, OTN, Metallurgiya i Toplivo, No. 6, p. 130, 1960.

Kornilov, I. I., Mikheyev, V. S., Chernova, T. S. and Markovich, K. P. Sb. "Titan i yego splavy, " Izd-vo SSSR, NO. 7, p. 141,. 1962.

Grum-Grzhimaylo, N. V. and Gromova, V. G. Coll. "Titanium and I ts Alloys" (Sb. "Titan i yego splavy"). Izd-vo AN SSSR, NO. 7, p. -36, 1962.

PHASE DIAGRAM OF THE SYSTEM Ti-O2 AND SOME PROPERPIES

OF THE ALLOYS OF THIS SYSTESI

I. I, Kornilov and V. V. Glazova

The character of the in te rac t ion between titanium and oxygen and the equilibrium diagram of t h i s system heretofore have been based on the concept of the existence of a wide region of a so l id solutions of titanium with oxygen and on the existence of the compounds TiO, Ti203 and Ti02 i n t h i s system ( f i g . 1 ) .

The var ia t ion i n the physicochemical, mechanical and other proper t ies of the a l loys of the system Ti-O2 has been a lso represented u n t i l now on the bas i s

of a wide region of i n t e r s t i t i a l - t ype a sol id solutions, up t o 32 a t .percent O2 ( re f s . 1-7). The l i t e r a t u r e contains only l imited data on de ta i led s tudies of the behavior of oxygen i n the region of a sol id solutions and on the in f lu - ence of ce r ta in possible reactions i n the a l loys i n the so l id s t a t e on t he properties of YS .

I n the l a s t few years, evidence has accumulated i n some s tudies on the pos s ib i l i t y of the formation of an ordered s t ructure i n the region of t he a solid solution of titanium with oxygen. Investigations of al loys of t i tanium with oxygen by methods of x-ray s t ruc tu ra l analysis ( re fs . 8 and 9) and by the e l e c t r i c a l res is tance method (ref . 10) revealed an anomalous var ia t ion i n prop- e r t i e s when the a l loy contained about 25 a t percent 02.

It was noted t h a t the ordered s t a t e of a l loys of t h i s system i s s tab le a t temperatures up t o 400 ( ref . 8). Ye. S. Makarov ( r e f . 11) used the x-ray method t o reaffirm the continuous nature of the var ia t ion i n the c rys t a l s t ruc- t u r e of the chemical compound of variable composition of a-phase-type i n the system Ti-02; i n the view of the authors of t h i s a r t i c l e , t h i s i s associated

with the continuous reaction of addit ion Ti + xO = TiOx + Q, where x can change

continuously from zero t o a value corresponding t o the boundary of phase inho- mogeneity. This purely physical in te rpre ta t ion of the behavior of oxygen i n a sol id solutions based on titanium has not accounted f o r the chemical ro le of t h i s metalloid i n the formation of various types of compounds i n a medium of metall ic sol id solutions.

DL, at. percent 40 SU

0000000000

5 7 75 20 W 30 O2, w t percent

Figure 1. Equilibrium phase diagram of a l loys of t h e system Ti-O2 (according t o t h e d a t a of reference 5). 1, one phase; 2, mixture of phases; 3, s t a r t of fusion; 4, p a r t i a l fusion; 7, complete fusion.

A n ana lys i s of t h e d a t a on t h e i n t e r a c t i o n of metals of group I V of t h e per iodic system wi th oxygen has enabled one of t h e authors ( re f . 12) t o postu- l a t e a poss ib le formation of t h e compound T i 0 i n t h i s system. This i s con- 3 firmed i n p a r t i c u l a r by a smooth maximum on t h e cons t i tu t ion diagram of t h e system Ti-O2 corresponding t o t h e region of 25 at. percent O2 ( f i g . 1). The

expressed arguments concerning poss ib le suboxide compounds of t i tanium with a meta l l i c bond character follow from an analys is of t h e chemical p roper t i e s of t i tanium and i t s tendency t o form in te rmeta l l i c compounds with e lec t ronegat ive elements ( re f s . 1 2 and 13).

Considering the pronounced a c t i v i t y of oxygen atoms i n i n t e r s t i t i a l s o l i d solut ions , one could assume t h e formation of s i m i l a r compounds from t h e a so l id so lu t ion i n t h e system Ti-O2 on slow cooling o r prolonged exposure t o low tempera ture conditions.

Later , on t h e b a s i s of t h e very incomplete inves t igat ions of Hurlin ( r e f . 14) i n t o t h e s t r u c t u r e of t h e sca le and inves t iga t ions i n t o the dependence of t h e e l e c t r i c a l r e s i s t ance of c a s t a l loys on t h e composition carr ied out by

Wasilewsky ( r e f . 15)) hypotheses were a l s o advanced concerning t h e poss ib le ex- i s t ence of the compounds Ti60 and Ti30.

Al l of t h e above l eads t o t h e conclusion t h a t the nature of t h e chemical i n t e r a c t i o n between t i tanium and oxygen i s f a r from being a s simple a s would follow from t h e phase diagram ( f i g . 1) given i n Ransen ' s handbook ( re f . 5 ) .

Attr ibut ing a major t h e o r e t i c a l and p r a c t i c a l importance t o t h e problem of t h e i n t e r a c t i o n of t i tanium with oxygen and t o t h e e lucidat ion of t h e chem- i c a l nature of the a l loys of t h i s system, we ca r r i ed ou t a de ta i l ed study of t h e system Ti-O2 and t h e range of concentrations from zero t o 35 a t - p e r c e n t 02,

The a l loys were prepared by fus ion i n an arc furnace with a nonconsumable e lec t rode i n an argon atmosphere.

The s t a r t i n g mater ia l f o r t h e prepara t ion of t h e a l l o y s was iodide titanium (99.9 percent TL) with the following main impuri t ies: M g (0.01 percent ) , S i (0.03 percent) , Al (0.01 percent) , Fe and N i (< 0.01 pe rcen t ) , C r (0.01 ~ e r c e n t ) , O2 (0.01 ~ e r c e n t ) , and N2 (0.01 percent) .

Oxygen was introduced i n t o t h e a l loys i n t h e form of a Ti-O2 master a l loy

containing 15.8 w t percent . The master a l l o y was prepared by melting b a r s pressed from t-jctanium and t i tanium d i m i d e of 99.93 percent p u r i t y i n an a r c f i rnace .

The above method was used t o prepare a l loys containing 0, 1, 3, 5 , 7, e t c . a-tx percent oxygen up t o 35 at. percent . .

Alloys of 10 compositions were subjected t o chemical ana lys i s by using t h e vacuum fus ion method. Results of t h e analys is showed t h a t t h e oxygen content of t h e i n i t i a l mixture was i n good agreement with t h e d a t a of t h e chemical analys is .

The c a s t a l loys were subjected t o homogenizing annealing i n vacuum a t 800' f o r 1000 hours.

After t h e homogenizing annealing at 800') t h e a l loys were annealed a t 400, 600, 800, 850, 1000 and 1 4 0 0 ~ f o r 600, -400, 1000, 100, 100 and 2 hrs, respec- t i v e l y , and quenched i n i c e water. -

I n the study of t h e a l loys , use was made of methods of physicochemical analys is developed by N. S. Kurnakov, which involved t h e p l o t t i n g of "composition-property" phase diagrams ( re f s . 16. and 17).

Such methods included microscopic and x-ray s t r u c t u r a l analyses, measure- ment of microhardness, e l e c t r i c a l res is tance , and temf.

The microhardness was measured with a PMT-3 instrument under a load of 200 g using t h e method described i n reference 18.

The made up o

The s ince all

be subjec

cas t ing t measured

The a l l o y with 25 a t - p e r c e n t O2 i s characterized by t h e presence of s l i p l i n e s

i n the s t r u c t u r e ( f i g . 213). The same s t ruc tu re was observed i n a l loys with a higher oxygen content, up t o 30 at .percent ( f i g . 2e). The microstructure of t h e a l l o y with 35 percent oxygen i s shown i n f igure 2f .

Microscopic analys is of a l loys quenched from 800 showed t h a t those with 13, 1 4 and 16 a t percent O2 were two-phase a l loys , and t h a t t h e s t r u c t u r e of

t h e remaining ones was polyhedral. It should be noted t h a t a l l specimens of a l loys contaiaing more than 10 a t .percent O2 were covered with cracks and

pores whose quant i ty increased with r i s i n g oxygen content.

Figure 2. Microstructures of al loys of the system Ti-O2 with the

following content: a, 5 percent 02, quenching a f t e r annealing a t

600, x 500; b, 10 percent 02, quenching a f t e r annealing a t 600,

x 500; c, 16 percent 02, quenching a f t e r annealing a t 6000, x 500;

d, 25 percent 02, quenching a f t e r annealing a t 6000, x 200; e , 30

percent 02, quenching a f t e r annealing a t 800, x 200; f , 35 per-

cent 02, cast s t a t e , x 200.

Alloys quenched from 850' had a polyhedral structure, with the exception of the a l loy with 25 at .percent 02, which retained the s l i p l i nes a t a l l quench-

ing temperatures.

I n the analysis of the microhardness of al loys of the Ti-O2 system

quenched from 400 and 6000, the "microhardness- composition" curves displayed two singular minima corresponding t o compositions with 14.5 and 25 at.percent o2 ( f ig . 3a).

The isotherm a t 800O has a noticeable in f lec t ion on the curve a t 14.5 at. percent 02, and a marked minimum a t 25 at . percent 02.

Isotherms a t 1000 and 1400 of the "microhardness-composition" curves display singular minima f o r the composition with 25 percent 02.

It should be emphasized tha t one group of a l loys i n the cast s t a t e exhibited a microhardness maximum i n the a l loy with 25 at .percent 02, which fo l -

lowing heat treatment a t 800' changed in to a minimum.

Figure 3b shows the dependence of the e l ec t r i ca l resistance on the compo- s i t i o n of a l loys quenched a f t e r holding a t 800, 1000 and 1 4 0 0 ~ .

On quenching from 800') the e l ec t r i ca l resistance r i s e s abruptly from 45.8 mohm/cm f o r pure titanium t o 158 mohm/cm f o r the a l loy with 10 at. percent 02.

I n the a l loy with 15 at .percent 02, the e l ec t r i ca l resistance r i s e s sharply,

reaching 466 mohm/cm; t h i s i s followed by a r i s e t o TOO mohm/cm f o r the alloy with 22 at .percent 02, then by a sharp decline i n e l ec t r i ca l resistance.

The alloy with 25 at.percent O2 has a resistance of 150 mohm/cm. As the

oxygen content increases, the e l e c t r i c a l resistance r i s e s t o 639 mohm/cm.

An analysis of the curve representing the e l e c t r i c a l resistance of alloys quenched from 1000 and 1 4 0 0 ~ versus composition shows the presence of a singu- l a r minimum a t 25 at .percent 02. It should be noted tha t i n many cases a t 25

at .percent 02, the cast specimens display a maximum which a f t e r a prolonged an-

nealing of the specimens changes in to a minimum.

Let us examine the dependence of the temf of alloys of the Ti-O2 system

on the oxygen content, i n a couple with copper a f t e r quenching from 800, 1000 and 1 4 0 0 ~ ( f ig . 3c)

On quenching from 800, the temf decreases sharply from pure titanium (30 mv/deg) t o a composition with 14 at.percent O2 (-78 m~/deg). It should be

17

noted that at a content of 5 at.percent 02, the temf changes sign, indicating

a change in the type of conduction from hole to electron conduction. In the alloy with 25 percent 0 the value of temf is at a minimum. 2'

On the isotherms at 1000 and 1400~) a singular minimum is preserved only in the composition with 25 at.percent 02.

6 f.2 I8 2 4 JJ 36 02, wt percent

Figure 3. Dependence of the microhardness (a), electrical resistance (b) and temf (c) on the composition of alloys of the system Ti-O2 after quenching from various temperatures.

Preliminary data of x-ray s t r u c t u r a l analys is show t h a t the a l l o y wi th 25 a t . percent O2 a t temperatures up t o 1 4 0 0 ~ has one supers t ructure l i n e , while no

superstructure l i n e s havethus f a r b e e n observed i n t h e a l l o y with 14.5 a t . percent 0 under these conditions of heat treatment. 2

Thus, based on the r e s u l t s of micros t ructura l ana lys i s and on t h e ftcomposition-property" diagrams i n the concentration range studied,one can assume t h a t i n t h e Ti-O2 system the re a r e two new compounds: Ti60 and Ti30.

The nature of t h e "composition-property" chemical diagrams a t 800' and a l so data of t h e microscopic analys is lead t o t h e conclusion t h a t the compound Ti 0 i s s t a b l e up t o 820-830'. 6

The compound Ti 0 with an ordered s t r u c t u r e i s apparently s t a b l e above 3 1400, s ince the s ingular character of t h e "composition-propertytt diagrams a t t h i s temperature remains unchanged.

A study of t h e s t a t e of t h i s compound a t higher temperatures up t o the melting point ( 1 9 0 0 ~ ) requires a spec ia l inves t igat ion.

The r e s u l t s of the present study have produced a new equil ibrium phase diagram of t h e a l loys of t h e Ti-O2 system f o r compositions containing l e s s than

35 a t .pe rcen t 02. It follows from t h i s diagram t h a t the compounds Ti60 and

and T i 0 a re formed i n the Ti-O2 system. 3 The s i m i l a r i t y between t i tanium and zirconium and t h e nature of t h e i r in-

t e r a c t i o n with oxygen leads t o t h e assumption t h a t the compound Zr60 and Z r 0 3 may e x i s t i n the system Zr-02.

The new compounds Ti60 and T i 0 es tabl ished i n the present work, and the 3 regions of t h e i r existence on the phase diagram of the Ti-O2 system a r e of

major importance i n t h e metal chemistry and physical metallurgy of t i tanium al loys . These new compounds should serve a s a bas i s f o r t h e study of equi l ib- r i a i n complex t i tanium systems with oxygen, and f o r the e lucidat ion of the influence of oxygen on t h e physicochemical and mechanical p roper t i e s of t i t a - nium and i t s a l loys ( r e f . 19).

I n the l i g h t of what was s t a t e d above, it appears very i n t e r e s t i n g t o study t h e influence of oxygen on t h e c h a r a c t e r i s t i c s of the s t a b i l i t y of the chemical bond, s ince it i s these c h a r a c t e r i s t i c s which, i n the f i n a l analysis , determine t h e degree of s t a b i l i t y of t h e a l loys i n appl ica t ions a t high temperatures.

02, a t . percent Figure 4. Phase diagram of a l loys of the system Ti-O2 (based on t h e d a t a of t h e present work).

o, s t ruc tu re of t h e a s o l i d so lu t ion ;@, a + y phase;^, a + 6 phase.

The pe r t inen t da ta f o r the Ti-0 system which a r e avai lable i n t h e l i t e r a - 2 t u r e a r e scarce and p e r t a i n t o a concentration range of not more than 20 a t . percent 02.

To solve t h i s problem, we undertook de ta i l ed inves t igat ions of t h e thermal expansion of the a l loys of the Ti-O2 system i n t h e concentration range from

zero t o 32 a t -pe rcen t O2 a t temperatures up t o 800'. This study was made with

an ind ica to r di latometer ( r e f . 20), using specimens quenched from 800' a f t e r soaking f o r 1000 hrs .

The heating was carr ied out a t the r a t e of 4 deg/min.

I n order t o compare t h e Ti-O2 system with t h e equil ibrium phase diagram

( f i g . ?a), w e show t h e dependence of t h e r a t i o A 111 on t h e composition of t h e a l l o y a t 100, 200, 300, 400, 500, 600, 700 and 800' ( f i g . 5b).

It follows from t h i s f i g u r e t h a t a l l the isotherms a re q u a l i t a t i v e l y s i m i - l a r i n character . A t first, when t i tanium i s alloyed with oxygen, t h e thermal expansion a t every given temperature shows a c e r t a i n decrease. A r e l a t i v e l y s l i g h t minimum corresponds t o t h e composition Ti6O. A f u r t h e r r i s e i n oxygen

content causes an increase i n thermal expansion up t o 23 a t .percent 0 and 2' t h i s i s followed by a precipi tous decline. A marked s ingular minimum corresponds t o t h e composition T i 0. 3

5 10 75 ZLI 25 3U 35 02, a t . percent

Figure 5. Comparison wi th the equilibrium phase diagram ( a ) of t h e dependence of the thermal expansion (b) and i t s coef f i c ien t ( c ) on the com- pos i t ion of a l loys of the system Ti-02.

From these data, values of t h e coef f i c ien t of thermal expansion a a s a function of t h e composition f o r t h e temperature range of 20-loo0 were ca lcula ted (fig. 5c) . It follows from t h i s f i g u r e t h a t the concentration dependence a is q u a l i t a t i v e l y s imi la r i n character t o t h e dependence of A 1/1 on t h e composition ( f i g . 5b).

The d a t a obtained on the thermal expansion of a l loys o f t h e Ti-O2 system

over a wide concentration range lead t o the conclusion t h a t when t i tanium i s alloyed with oxygen, t h e s t a b i l i t y of t h e chemical bond i n t h e a l loys increases up t o 14.5 a t .percent 02. The character of the concentration dependence of

t h i s c h a r a c t e r i s t i c i s dist inguished by t h e presence of s p e c i f i c po in t s eorre- sponding t o t h e compounds Ti60 and T i 0. 3

It should be noted t h a t the compound T i 0 i s p a r t i c u l a r l y characterized by 3 sharp s ingular extrema of t h e "composition-property'' curves; t h i s f e a t u r e s e t s it apar t a s a chemical species whose interatomic bonds i n the c r y s t a l l a t t i c e are very strong.

I n connection wi th t h e inves t igated novel character of the chemical i n t e r - act ion and phase equilibrium i n t h e Ti-O2 system, the study of t h e influence of

oxygen on t h e creep of t i tanium a t various temperatures appeared of g r e a t in - t e r e s t . I n con t ras t t o t h e s tud ies of o the r authors ( re f s . 1-4)) t h i s property was studied over a wide range of oxygen concentrations (up t o 18 at .percent) .

To t h i s end, a l loys were prepared containing 0.02, 0.39, 0.75, 1.25, 1.66, 3, 4, 8, l o , 15 and 18 a t , p e r c e n t 02. Alloys containing more than 4 a t .percent O2 were prepared by the powder method a t a s i n t e r i n g temperature of 1500~.

Alloys of a l l compositions were annealed at 800' f o r 200 h r and were slowly cooled from t h i s temperature.

Tes ts f o r hot hardness were made with a VIM-1 u n i t a t pressures of 10-3-

mm Hg. The hardness was determined by indenting t h e specimen wi th a d ia- mond pyramid having a leap angle of 136'. The load on the indenter was 1 kg. The dura t ion of deformation a t each temperature was 0.5, 5 and 50 min. The measurements were made a t 300, 400, 500, 600 and 700 ( t a b l e 1).

The r e s u l t s of t h e measurements were t r ea ted graphical ly by p l o t t i n g t h e diagonal of t h e indentat ion versus log time f o r various temperatures. It was thus es tabl ished t h a t the time dependence of the s i z e of the diagonal of the indentat ion a t each temperature i s described f a i r l y r igorously by t h e equation

where a and b a r e parameters dependent on t h e nature of the a l loy , t h e t e s t i n g temperature and t h e load on the indenter; T i s the t e s t i n g time.

Parameters a and b were determined ( t a b l e 2) from the working graphs f o r the dependence of t h e logarithm of t h e holding time under load.

On the b a s i s of these da ta and from the equation

proposed i n references 22 and 23, a ca lcula t ion was made of t h e r a t e of creep a t the i n s t a n t when a given value of t h e indentat ion diameter was reached.

I n references 21 and 22 it was shown t h a t the concentration dependence of t h e log of t h e r a t e of creep f o r a s e r i e s of a l loys was i n q u a l i t a t i v e agreement with t h e concentration dependence of t h e r a t e of creep obtained during extension.

Values of l o g Vd of a l loys of t h e Ti-O2 system f o r d = 0.12 mm ( a t 300,

400 and 500') and d = 0.18 mm ( a t 600 and 700), calculated from equation (2) are shown i n Table 2.

We s h a l l compare the concentration dependence of t h e log of t h e r a t e of creep, log Vd ( f igs . 6b and c ) , wi th the equilibrium phase diagram of t h e sys-

tem ~ i - 0 ~ ( f i g . 6a) .

The concentration dependences of log V shown on t h e graph give a c l e a r d representat ion of t h e behavior of t h e a l loys of the Ti-O2 system a t high tem-

pera tures under load. It should be noted t h a t i n an analys is of these r e s u l t s , the highest s t a b i l i t y of t h e a l loys under load corresponds t o t h e lowest nega- t i v e values of log Vd.

A t 300, t h e isotherm of log Vd i s characterized by an appreciable drop i n

the concentration range from zero t o 2 a t .pe rcen t , where oxygen has p r a c t i c a l l y no influence on the change i n log Vd, and hence, on the s t a b i l i t y of t h e a l loys

under load.

A f u r t h e r increase i n oxygen content causes a sharp drop on t h e curve representing t h e concentration dependence of log Vd; t h i s corresponds t o an

increase i n t h e s t a b i l i t y of the a l loys under load, and log V becomes 4 times d smaller than i n pure titanium. A comparison of t h i s curve with t h e equil ibrium

mw~n~~n+mow~m

0W*~?nlNwW~-bb

"""""""0-0-0-0-

ddodooooooo

" 3 6 9 12 1.5 18 02, a t , percent

Figure 6. Comparison of t h e equilibrium phase diagram with t h e dependence of t h e creep r a t e on the composition of t h e a l loys of t h e system Ti-02.

phase diagram of t h e Ti-O2 system shows t h a t a sharp increase i n t h e res i s t ance

t o p l a s t i c deformation, according t o t h e physicochemical theory of high- temperature s t rength ( r e f . 23)) i s associated wi th a s h i f t t o t h e two-phase region (a + y ) , i n which the second (y) phase i s a s o l i d so lu t ion based on t h e compound Ti60 and belonging t o t h e c l a s s of Kurnakovls compounds.

The isotherms of log Vd a t 400, 500 and 6000 a re completely s i m i l a r i n

character , and i n the concentration range of 2-8 a t .percent 0 the re i s even 2 observed a tendency toward an increase i n log V o r a decrease i n t h e r e s i s t - d ance t o t h e p l a s t i c deformation of the a l loys a t these temperatures.

The isotherm of l o g Vd a t 7000 f o r the a l l o y with 10 at .percent (3.58 w t

percent) O2 does not show any increase i n the res i s t ance t o p l a s t i c deformation,

as i n t h e case of o the r temperatures, and t h i s again corresponds t o t h e estab- l i shed phase diagram of t h e Ti-O2 system, s ince a t 700' t h e a l l o y with 10 a t .

percent O2 remains a single-phase a l loy .

Thus, a complete cor re la t ion i s observed between t h e nature of t h e chemi- c a l i n t e r a c t i o n i n the Ti-O2 system, the type of "composition-creeptt diagram

a t various temperatures, and t h e character of t h e atomic i n t e r a c t i o n i n t h i s system.

Summary

1. Methods of micros t ructura l and x-ray s t r u c t u r a l analys is as we l l a s measurements of microhardness, e l e c t r i c a l res is tance , and temf were used t o study t h e a l loys of t h e Ti-O2 system quenched a f t e r annealing a t various tem-

pera tures i n t h e concentration range of zero t o 35 a tepercen t 02.

2. Results of these inves t igat ions and the "composition-propertyt' d ia- grams obtained made it poss ib le t o e s t a b l i s h t h e existence of t h e new compounds Ti60 and T i 0. 3

3. The concentrat ion and temperature l i m i t s of t h e existence of these compounds were determined, and a new equil ibrium diagram of t h e Ti-O2 system

was proposed. The compound Ti60 i s s t a b l e up t o 820-830, while t h e compound

Ti 0 i s thought t o be s t a b l e above 1 4 0 0 ~ . The compositions of t h e compounds 3 should be characterized by a maximum degree of ordering of oxygen atoms i n t h e l a t t i c e of t h e a s o l i d solut ion.

4. The thermal expansion of the a l loys of t h e Ti-O2 system was studied

over a wide temperature and concentration range. On t h e bas i s of t h e d a t a obtained, t h e dependence of t h e coef f i c ien t of thermal expansion on t h e composi- t i o n of t h e a l loys of t h e Ti-O2 system w a s es tabl ished. Analysis of t h e con-

cent ra t ion dependence of t h i s property l ed t o t h e conclusion t h a t t h e s t a b i l i t y of the chemical bond between the atoms of t i tanium and oxygen increases i n t h e c rys ta l l a t t i c e of a l loys and compounds T i 0 and T i 0. 6 3

5 . The hot hardness of the a l loys of t h e Ti-O2 system were s tudied i n t h e

concentration range of zero t o 18 a t - p e r c e n t and i n t h e temperature range of 300-700 f o r various holding times under load a t each temperature. From the data obtained, t h e r a t e s of p l a s t i c flow of t h e a l loys of t h i s system a t t h e i n s t a n t when a given value of the indenta t ion s i z e was reached were ca lcula ted .

6. The general nature of the influence of oxygen on the behavior of titanium under load at various temperatures was established, and a correlation between this dependence and the new equilibrium phase diagram of the Ti-O2 system

was noted.

Finally, the authors express their thanks to T. F. Zhuchkova, who was of great assistance in the execution of this work.

REFERENCES

1. Borisova, A. A. Coll. "TitanSum and Its Alloys," Izd-vo AH SSSR, No. 3, p. 23, 1960.

2. Jehknis, A. and Worher, H. J. Inst. Metals, Vol. 80, No. 4, p. 157, 1951.

3. Yakimova, A. Ya. Influence of Hydrogen and Oxygen on the Properties and Structure of Titanium Alloys. Author's abstract of candidate's disser- tation (~li~aniye vodoroda i kisloroda na svoystva i struktum titanovykh splavov. Avtoref . kand . diss . ) . Institut metallurgii imeni A. A. Baykova (A. A. Baykov Institute of ~etallurgy), Moscow, 1959.

4. Suiter, J. J. Inst. Metals, Vol. 83, part 10, p. 460, June 1955.

5. Hansen, M. and Anderko, K. Structure of Binary Alloys (Struktura dvoynykh splavov) . Metallurgizdat, Vol. 2, 1962.

6.. E;hrlich, P. P, z. Anorg. Chem., Val. 247, p. 53, 1941.

7. Bamps, E., Kessler, H. and Hansen, M. TASM, Vol. 45, p. 1008, 1953.

8. Anderson, S., Collen, B.,.Kuylenstierna, U. and Magnelli, A. Acta Chem. &.and., Vol. 7, No. 10; p. 1641, 1957.

9. Nowgtny, H. and Dimakopoulu, E. Monatshf. f. Chem., Vol. 90, No. 5, P. 620, 1959.

10. Wasilewsky, R. Trans. IUHE, p. 3, November 1957.

11. Makarov, Ye. S. and Kuznetsov, L. M. Zhurnal Strukturnoy Khimii, Vol. 1, NO. 2, p. 170, 1960.

2 Kornilov, I. I. Trudy Komissii po analiticheskoy khimii AN SSSR (~rans- actions of the Commission on Analytical Chemistry of the Academy of Sciences of the USSR), Izd-vo AN SSSR, Vol. 10, p. 18, 1960.

13. --- Izv. AN SSSR, OTN, Metallurgiya i Gornoye Delo, No. 1, p. 152, 1963.

14. Hurlen, T. J. Inst. Metals, Vol. 89, No. 4, 1960.

5 . Wasilewsky, R. J. Trans. A m , No. 4, p. 8, 1962.

Kurnakov, N. S. Introduction to Physicochemical Analysis (~vedeniye v fiziko-khimicheskiy analiz) . Izd-vo AN SSSR, 1938.

Pogodin, S. A. and Anosov, V. A. Fundamentals of Physicochemical Analysis. Izd-vo AH SSSR, 1947.

Glazov, V. M. and Vigdorovich, V. N. Microhardness of Metals (~ikrotverdostl metallov ) . Metallurgizdat, 1960.

Kornilov, I. I. and Glazova, V. V. Doklady AN SSSR, Vol. 150, No. 2, P. 313, 1963.

Mints, R. S. Zav. lab., No. 12, p. 1526, 1958.

Osipov, K. A. and T'ien Te-chfeng. Izv. AH SSSR, Metallurgiya i Toplivo, No. 4, P. 77, 1959.

Osipov, K. A. Problems of the Theory and High-Temperature Strength of Metals and Alloys (Voprosy teorii zharoprochnosti metallov i splavov). Izd-vo AN SSSR, 1960.

Kornilov, I. I. Physiochemical Principles of High-Temperature Strength (~iziko-khirnicheskiye osnovy zharoprochnosti ) . Izd- vo fW SSSR, 1961.

EQUILIBRIUM DIAGRAM OF TEIE: QUATERNARY SYSTESI Ti-Al-Mo-V

E. N. Pylayeva and KO Chih-ming

The study of the phase equilibrium of alloys of the quaternary system Ti-Al-Mo-V adjacent to 'the titanium vertex of the tetrahedron (fig. 1) is of theoretical and practical importance, since this system can be used as the basic multicomponent system for the development of new high-strength and heat- resistant alloys of low density.

In its chemical properties, aluminum differs substantially from titanium and forms limited solid solutions and a series of metallic compounds with its a and @ modifications (refs. 1-3).

Vanadium and molybdenum are located in the fifth and sixth groups of the periodic system, close the titanium group,and are close to the latter in atomic radii, electronegativity and other properties. They are capable of forming continuous binary and ternary solid solutions with @-Ti and limited solid solutions with a-Ti (refs. 1 and 4). Vanadium and molybdenum are important alloying elements for high-strength titanium alloys having a @ structure.

The position of vanadium and molybdenum in the periodic system in relation to titanium and their similar chemical properties also account for their similar behavior in titanium alloys. Thus, for example, the binary systems Ti-Mo and Ti-V have the same type of phase diagram (ref. 1).

In the ternary system Ti-Mo-V, there is observed a continuous shift of the a and @ solid solutions and of the two-phase a + @ region from the system Ti-Mo to the system Ti-V. This is clearly indicated by the isothermal section of the ternary system Ti-Mo-V at 600' (fig. 2).

The phase regions a, a + @ and 8 shift from the side of Ti-Mo toward that of Ti-V, the region of the a solid solution expanding continuously from the side of Ti-Mo (up to 0.8 percent MO) to the side of Ti-V (2 percent V) . The boundary between the a + @ and @ region passes through the points of 28 percent Mo in the Ti-Mo system, 31 percent (MO + V) in the Ti- (MO:V = 1:1) system, and 22 percent V in the Ti-V system.

The similarity in the chemical properties of molybdenum and vanadium in relation to titanium explains the possibility of formation of similar phase

diagrams not only in the binary systems Ti-Mo and Ti-V but also in ternary systems in the portion rich in titanium, for example, in the systems Ti-Al-Mo and Ti-AL-V (refs. 5 and 6).

In order to study the phase equilibrium in the quaternary system Ti-Al- Mo-V, we investigated the ternary system Ti-A.1-Mo and the system Ti-Al- (MO:V = 1:1), which is the section of the concentration tetrahedron of the quaternary system originating at the edge of the binary system Ti-Al with a constant ratio of the weight concentration Mo:V = 1:1. The position of these two systems in the tetrahedron is shown in figure 1 and their investigated portions are shaded.

Figure 1. Concentration tetrahedron of the quaternary system Ti-A1-Mo-V.

V, wt percent Mo, wt percent

v M o V=7:7

Figure 2. Isothermal section of the ternary system Ti-Mo-V at 600.

Let us examine (figs. 3 and 4) the isothermal sections at 600' of the systems Ti-Al-Mo and ~i-Al-(MO:V = 1:l). A comparison of the isothermal sections of these systems at 6000 with the system Ti-Al-V (ref. 6) leads to the conclusion that in these three systems in the portion rich in titanium, the same phase regions are in equilibrium, namely:

a. Solid solutions based on a-Ti with a hexagonal close-packed structure;

b. Solid solutions based on @-Ti with a cubic body-centered structure;

c. Limited y solid solutions based on the compound TiAl with an ordered face-centered tetragonal structure;

Mo, wt Al, wt percent

50

Figure 3. Isothermal section of a part of the ternary system Ti- Al-Mo at 600.

Ti

Al, wt percent

Figure 4. Isothermal section of a part of the system ~i-Al- (MO:V = 1:l) a* 600~.

d. Two-phase a + f3, a + y, and f3 + y regions;

e. Three-phase a + f3 + y region.

The performed invest igat ion shows t ha t i n t he phase-equilibrium tetrahedron of the quaternary system Ti-Al-Mo-V, the above-indicated phase regions s h i f t s t ead i ly from the system Ti-Al-Mo v ia the intermediate system Ti-Al- (MO:V = 1:l) toward the system Ti-Al-V. For the sake of a c l ea r treatment of t he process of t h i s s h i f t , we s h a l l consider f i v e sections of t he phase-equilibrium tetrahedron of the quaternary system Ti-Al-Mo-V a t 600' with a constant titanium concentra- t i o n of 90, 80, 70, 60 and 50 w t percent ( f i g . 5 ) .

The sections with 90 and 80 percent Ti cut through t he a and a + f3 phase regions. I n the s h i f t from the Ti-Al-Mo system t o t he Ti-Al-V system, t h e f i e l d of the a so l id solution expands continuously from 1 percent Mo t o 2.5 percent V on the sect ion with 90 percent T i and from 1 percent Mo, 3 percent (MO-V) t o 4 percent V on t he sect ion with 80 percent Ti. The overwhelming majority of these sections belong t o t he a + f3 region.

The sect ion with 70 percent T i shows a + y, a + f3 + y, a + f3 and f3 phase regions. I n the s h i f t from the Ti-AX-Mo t o the Ti-Al-V system, the a + y region expands, and the a + f3 + y region narrows down. Awide f i e l d of t he a + f3 region is found i n t he middle port ion of t h i s section.

The regions of @ so l id solutions, which extend from the systems Ti-Al-Mo and Ti-Al-V, become joined together on t h i s section.

T L -3L'RL

Ti-Zff AL

XL TL-IgV T~-lOtlo

YQ%TL TL-ZffV 80% Tt Tb-2ff NO TL-3UV ~L'%TL T~-3ff MO

Figure 5. P a r a l l e l sections of the tetrahedron of the phase equilibrium of t he quaternary system Ti-Al-Mo-V a t 600 a t a constant titanium concentration of 90, 80, 70, 60 and 50 w t percent.

The sect ion with 60 percent T i i s dist inguished by the f a c t t h a t it d i s - p lays simultaneously the processes of gradual s h i f t of y, a + y, a + ,6 + y, a + f3, and (3 regions i n the tetrahedron, I n the course of t h e s h i f t from t h e Ti-Al-Mo system t o t h e Ti-Al-V system, t h e region of t h e p phase narrows down smoothly a t f i r s t , then expands, passing through the system Ti-Al- (MO:V = 1: 1).

A new phase region (p + y region) which s h i f t s s t e a d i l y from the Ti-Al-Mo system t o the Ti-A1-V system arlpears on t h e sec t ion wi th 50 percent TL. On t h i s sect ion, i n t h e por t ion adjacent t o the s ide of t h e Ti-Al system of t h e t e t r a - hedron, t h e complete s h i f t of t h e individual phase regions i s impaired under t h e influence of a complex in te rac t ion of t h e phases a t the aluminum vertex of t h e tetrahedron.

On t h e bas i s of t h e above inves t igat ion, we p lo t t ed a diagram of t h e phase equilibrium of t h e quaternary system Ti-Al-V-Mo i n t h e region of a l loys r i c h i n t i tanium a t 600' ( f i g . 6 ) .

I n t h e phase-equilibrium tetrahedron, the volume of t h e a s o l i d so lu t ion i s adjacent t o t h e s ide of t h e binary system Ti-& from zero t o 25 percent Al. The quaternary f3 s o l i d solut ion i s adjacent t o the face of t h e t e r n a r y system Ti-Mo-V when t h e t o t a l content of aluminum, molybdenum and vanadium i s over 22 percent . The quaternary y so l id so lu t ion based on TiAl extends from t h e binary system Ti-Al toward t h e i n t e r i o r of t h e tetrahedron. The c e n t r a l por t ion of t h e tetrahedron i s occupied by a two-phase a + p volume. The three-phase a + p + y volume borders on t h e two-phase a + f3, a + y, and f3 + y volumes and t r averses the tetrahedron from t h e face of t h e t e rna ry system Ti-Al-Mo t o t h e f a c e of t h e t e rna ry system Ti-Al-V.

Thus, a geometrical representa t ion of t h e studied por t ion of t h e phase equi- l ibr ium tetrahedron a t 6000 reveals t h e character of the in te rac t ion between t h e components and c l e a r l y shows t h e expansion of the phase regions i n t h e quatern- a ry system Ti-Al-Mo-V.

Figure 6. Phase equilibrium diagram of t h e quaternary system Ti-A1-Mo-V i n the region of a l loys r i c h i n t i tanium a t 6 0 0 ~ .

REFERENCES

Kornilov, I. I. and Budberg, P. B. Phase Diagrams of Binary and Ternary Titanium Systems (~iagrammy sostoyaniya dvoynykh i troynykh sistem titana). Publ. Acad. Sci. USSR, p. 22, 1961.

Grum-Grzhimaylo, N. V., Kornilov, I. I., Pylayeva, Ye. N. and Volkova, M. A. Dokl. AN SSSR, Vol. 137, No. 3, p. 599, 1961.

3. Kornilov, I, I. Metallovedeniye i termicheskaya obrabotka metallov, No. 2, p. 7, 1963.

4. Kornilov, I. I. and Polyakova, R. S. Izv. AN SSSR, OTN, Metallurgiya i Toplivo, No. 1, p. 85, 1960.

5. Kornilov, I. I., Pylayeva, Ye. N. and KO Chih-ming. Zh. Neorg. Khim., VO~. 8, NO. 2, p. 366, 1963.

6. Kornilov, I. I., Pylayeva, Ye. N. and Volkova, M. A, Sb. "Titan i yego splavy," Publ. Acad. Sci. USSR, No. 7, p. 89, 1962.

PHASE STRUCTURF: OF ALLOYS OF THE SYSTEM Ti-Al-Fe-Cr-Si WITH A CONSTANT CONTENT OF ALUMINUM AND SILICON

V. S. Mikheyev and K. P. Myasnikova

I n d u s t r i a l a l loys of the AT s e r i e s ( r e f . 1) are high-strength a l loys based on a-Ti alloyed with aluminum, chromium, iron, s i l i c o n and boron. This multicomponent system has been studied i n severa l works ( re f s . 2 and 3 ) . I n ref - erence 2, a s tudy was made of the system Ti-Al-Cr-Fe-Si-B with a var iable con- t e n t of aluminum (from zero t o 7.5 w t ~ e r c e n t ) and a constant content of chromium, i r o n and s i l i c o n (0.5 w t percent of each al loying element). I n reference3,phase transformations i n t h e system Ti-Al-Cr-Fe-Si with a constant content of aluminum (6.0 w t ~ e r c e n t ) and s i l i c o n (0.3 w t percent) and a var iable content of i ron and chromium were studied.

The object of the present inves t igat ion was a study of t h e phase equi l ibrium i n a l loys of the sec t ion of t h e tetrahedron Ti(+0.3 percent Si)-Al-Fe-Cr at a constant aluminum content (7.5 w t percent) . I ron and chromium were introduced i n the proport ion of 3:1, 1:l and 1:3, the t o t a l being up t o 30 percent. Hence- f o r t h , the corresponding r a d i a l sec t ions w i l l be termed sect ions I, I1 and 111.

The bas is f o r the p l o t t i n g of t h e equilibrium diagram of the a l loys of the se lec ted sec t ion of the five-component system was a method of s p a t i a l representa- t i o n of p a r t i a l multicomponent systems f o r any given number of components en- t e r i n g i n t o t h e composition of the so l id so lu t ion of t h e solvent ( r e f . 4) .

One of t h e v e r t i c e s of the concentration t r i a n g l e which we studied was made up of the a s o l i d solut ion wi th 7.5 w t percent Al an; 0.3 w t percent S i , and t h e o the r two were i r o n and chromium.

The chemical in te rac t ion of t i tanium with aluminum, chromium, i ron and s i l i c o n i n binary systems and a l so the s t r u c t u r e of ternary t i tanium a l loys a re described i n monographs ( refs . 5-7).

With t h e above-indicated elements, t i tanium forms a wide region of s o l i d solut ion and a narrow region of a s o l i d solut ion. As the temperature is lowered, the s o l i d so lu t ion based on @-Ti undergoes a eutectoid transformation wi th t h e p r e c i p i t a t i o n of the a so l id solut ion and of t h e corresponding in te rmeta l l i c compounds: T i S i i n the system Ti-Si, TiFe i n the system Ti-Fe, and TiCr2 i n 5 3 t h e system Ti-Cr.

The so lub i l i t y of each of the enumerated elements i n a-Ti i s 0.3-0.5 percent a t the temperature of the eutectoid transformation ( re f s . 8-10).

Aluminum ra i ses the temperature of the polymorphic transformation of titanium and forms a wide region of sol id solutions based on a-Ti.

An investigation of the propert ies of a so l id solutions i n t h e Ti-A1 system revealed the presence of chemical compounds corresponding t o t he composi- t ions ~ i~ i l l , Ti ~l and Ti2Al ( re f . 11). 3

In the three-component system Ti-Fe-Cr, the Q so l id solution i s s tab le over a wide temperature range. I ron and chromium lower t he temperature of t he po lporph ic transformation of titanium. The eutectoid decomposition of t h e Q phase i s associated with the formation of t he a phase, TiFe and TiCr2 ( re f .

12).

I n the other ternary systems Ti-Al-Fe and Ti-Al-Cr, on the polythermal sections a t a constant aluminum content of 7.5 percent, phases based on a- and @-Ti are i n equilibrium with in termetal l ic compounds corresponding t o t he com- posit ion TiFe i n the f i r s t system and T i e r 2 i n the second ( re f s . 1 3 and 14). Star t ing Materials and Method of Preparation of t he Alloys

The compositions of the investigated a l loys a re shown i n the t ab le . The s t a r t i ng materials f o r t he preparation of the samples were: TGOO titanium sponge, e l ec t ro ly t i c chromium, KKL s i l icon, A00 aluminum, and i ron (0.03 percent C; 0.01 percent Mn; 0.008 percent P; t r aces of s).

CITENICAIL COMPOSITION OF TIEE AS;LOYS STUDIED (IN w t PERCENT)

Note: All al loys contain 0.3 w t percent S i and 7.5 w t percent Al. Note: Al l commas represesent decimal points.

-- -. - - - I _ _ Section

I11 I

I 0,05 0,125 0,25 0,625 1,25 1,875 2,50 3,75 5,O 795

0,05 0,125 0,25 0,625 1,25 1,875 2,50 3,75 5,O

1 715

Samples of the a l loys weighing 20 g were prepared by arc fus ion i n argon. The weight l o s s was no more than 0.3 percent . The c a s t samples were forged i n a i r i n t o rods 7 mm i n diameter a f t e r being heated a t 1 2 0 0 ~ .

The heat treatment was carr ied out i n s e a es. To prevent the t i tanium al loys from react ing w aced i n a tube made of t h i n molybdenum sheet .

The heat treatment consisted i n annealing 800 and 500 wi th a holding time of 10, 15, 30

After annealing a t 1100, 1000 and 800, quenched i n water, and t h e o the r was furnace-

The study of t h e p a r t i a l system was c a r r u r a1

RKD camera.

Results

annealed s t a t e

on &Ti. The s phase, with t h sec t ion I, whe

A t 1100~ i n the range of concentrations of Fe -t C r from zero t o 20 w t percent of sec t ions I and I11 and up t o 30 w t percent of sec t ion 11, t h e a l loys have the s t r u c t u r e of the ,3 s o l i d solut ion. Quenching from t h i s temperature causes a ,3 + a f martensi te transformation ( f ig . l b ) i n a l loys containing up t o 5 w t percent (Fe + ~ r ) . I n higher a l loys , t h e p phase becomes f ixed ( f i g . l c ) .

I n a l loys with 30 w t percent (Fe -t C r ) of sect ions I and 111, the precipi - t a t i o n of a second phase i s observed along the boundaries and t h e f i e l d of B grains ( f i g . I d and e ) . X-ray d i f f r a c t i o n analysis established t h a t t h e sec- ondary phase p rec ip i t a t ing from the ,3 so l id solut ion i s the intermetalZic compound' TiFe (6 phase) i n a l loys of sec t ion I, and i n a l loys of sec t ion 111, the in te rmeta l l i c compound TiCr2 of hexagonal modification (y phase).

Figure 1. Microstructure of the al loys a f t e r various heat treatments, x 340. a, a l loy of sect ion I with 30 percent (Fe + cr ) , cast ; b , a l loy of section I1 with 5 percent (Fe + cr) , quenching from l l O O O ; c, a l loy of section I with 7.5 percent ( ~ e + cr) a t 1 1 0 0 ~ ; d, a l loy of sect ion I with 30 percent (Fe + cr ) , quenching from 1 1 0 0 ~ ; e , a l l oy of section I11 with 30 percent (Fe + c r ) , quenching from 1 1 0 0 ~ ; f , a l l oy of section I with 2.5 percent (Fe + c r ) , quenching from 10000; g, a l l oy of sect ion I with 0.2 percent (Fe + Cr), quenching from 800; h, a l loy of sect ion I1 with 7.5 percent (Fe + C r ) , quenching from 800; i, a l loy of section I1 with 20 percent ( ~ e + C r ) , quenching from 800'; j, a l l oy of section I11 with 7.5 percent (Fe + C r ) , annealing a t 6000.

Figure 1. (Concluded)

Figure 2a shows an isothermal sec t ion of t h e tetrahedron T i (+0.3 percent ~ i ) - A l - ~ e - ~ r with a constant aluminum content (7.5 w t percent) a t 1 1 0 0 ~ . The main por t ion of t h e concentration t r i a n g l e i s occupied by the five-component f3 s o l i d solut ion. The boundaries of t h e two-phase regions B + 6 and f3 + y were not accura te ly determined, and they are therefore represented by broken l i n e s .

The compositions of the a l loys on the isothermal sec t ion a t 1100 which undergo a mar tens i te transformation a r e marked with crosses.

On quenching from 100oO, the a l loys containing i ron and chromium (up t o 2.5 w t percent) together with the /3 and a t phases contain the equil ibrium a phase formed a s a r e s u l t of the polymorphic f3 + a transformation ( f i g . l f ) . The amount of the a s o l i d so lu t ion i n the a l loys decreases a s the sum of i r o n and chromium increases.

The pure @ s o l i d solut ion becomes f ixed i n a l loys containing 7-20 w t percent ( ~ e + ~ r ) of sec t ion I. I n the microstructure of a l loys with 5 w t pereent of the a l loying components i n sec t ions I1 and 111, martensi te needles a r e observed; t h e i r h ighes t quant i ty is found i n the a l l o y of sec t ion 11, a t t h e r a t i o Fe:Cr = 1:l. An increase i n the content of i r o n and chromium i n t h e a l l o y s of these sec t ions causes a s t a b i l i z a t i o n of the /3 phase. A t 1000, t h e region of existence of the @ so l id solut ion narrows down considerably owing t o t h e appearance of t h e two-phase a + B region and the expansion of both the @ + 6 and f3 + y regions as a r e s u l t of a decrease i n the s o l u b i l i t y of the in te rmeta l l i c compounds i n p-Ti with increasing temperature ( f i g . 2b).

F e Cr Fe Cr

Figure 2. Isothermal sec t ions of t h e tetrahedron: a, a t 1 ,100~; b, a t 1 0 0 0 ~ ; c, a t 8 0 0 ~ ; d, a t 5000.

After annealing a t 800 and quenching from t h i s temperature, t h e a l loys r i c h i n t i tanium and containing up t o 0.2 w t percent ( ~ e + ~ r ) have the polyhedral s t ruc tu re of t h e a so l id solut ion ( f i g . l g ) . I n t h e concentration range of i r o n and chromium of 0.5-15 w t percent, a l l t h e a l loys cons i s t of two phases ( a + 8) .

It should be noted t h a t t h e microstructure of a l loys with 7.5 w t percent ( ~ e + ~ r ) r e f l e c t s the p e r i t e c t o i d character of t h e i n t e r a c t i o n of t h e phase components ( f ig . l h ) . This may be a confirmation of t h e phase diagram of Ti-A1 proposed by Zwicker e t a l . ( r e f . 15) , with a pe r i t ec to id nature of t h e forma- t i o n of t h e a phase by the react ion 8 + a2 + a.

However, the avai lable data pertaining t o t h i s problem a r e i n s u f f i c i e n t t o allow any d e f i n i t i v e conclusions. A f u r t h e r s tudy of t h e phase transformations i n t h e a so l id solut ion of t i tanium i n binary, t e rna ry and multicomponent systems wi th aluminum i s necessary.

Alloys with a high t o t a l content of i ron and chromium (20-30 w t percent) have a two-phase s t r u c t u r e 8 + 6 (a l loys of sec t ion I) o r 8 + y (a l loys of

sec t ion 111) o r a three-phase s t r u c t u r e f3 + 6 + y (al loys of sec t ion 11). A c h a r a c t e r i s t i c s t r u c t u r e of the three-phase s t a t e i s shown i n f i g u r e li.

I n t h e study of the microstructure of a l loys quenched from 800, no s ingle- phase s t r u c t u r e of t h e f3 s o l i d so lu t ion was observed, probably because we d id not inves t iga te t h e compositions of a l l o y s wi th 13-20 w t percent ( ~ e + C r ) .

On the bas i s of t h e s tud ies made i n reference 3 and data of micros t ructura l and x-ray s t r u c t u r a l analysis on t h e phase equil ibrium i n a l loys with higher o r lower content of i r o n o r chromium, it i s poss ib le t o pos tula te t h e exis tence of - a narrow region of a single-phase f3 s o l i d so lu t ion on t h e isothermal s e c t i o n a t 800.

Figure 2c shows a phase diagram of t h e sec t ion of the tetrahedron T i (c0.3 percent ~ i ) - A l - C r - ~ e a t 800'.

The five-component @ so l id so lu t ion at t h i s temperature i s i n a two-phase and three-phase equil ibrium with t h e a + y and 6 phases. The maximum so lub i l - i t y of the sum of i ron and chromium a t 800' i n t h e five-component a s o l i d solu- t i o n amounts t o no more than 0.4 w t percent.

Long annealing f o r 750 h r a t 500' l eads t o a complete eutec toid decomposi- t i o n of t h e @ s o l i d solut ion ( f ig . 1 3 ) . According t o the x-ray s t r u c t u r a l anal- y s i s , a l l the a l loys a t 500 have a three-phase s t ruc tu re a + S + y.

A phase diagram a t 500 i s shown i n f i g u r e 2d.

Thus, t h e inves t igat ion of t h e five-component system Ti-Al-Fe-Cr-Si con- ta in ing up t o 30 percent ( ~ e + ~ r ) a t 1100, 1000, 800 and 500 has shown t h a t a and f3 s o l i d so lu t ions and in te rmeta l l i c phases TiFe and TiCr2 a r e formed i n

t h i s system. However, a more complex character of in te rac t ion can be postula ted i n t h i s system. I n pa r t i cu la r , as was indicated above, the formation of t h e chemical compound T i Al (a2 phase) i s poss ib le . Because the nature of t h e in- 3 t e r a c t i o n i n t h e binary system Ti-Al i n t h e region of the a so l id so lu t ion has not been d e f i n i t e l y established, and t h e influence of i r o n o r chromium i n t h e three-component systems Ti-Al-Fe and Ti-Al-Cr has not been elucidated, i n p lo t - t i n g the isothermal sec t ions we did not take i n t o account the regions of phase e q u i l i b r i a wi th t h e a2 phase.

The inves t iga t ion which was carr ied out makes it possible t o draw some conclusions wi th regard t o the influence of aluminum on t h e chemical in te rac - t i o n of t i t a n i u m w i t h chromium and iron. Aluminum r a i s e s the temperature of the polymorphic transformation, a s indicated by the phase e q u i l i b r i a on the isothermal sec t ions a t 1000 and 8 0 0 ~ . Furthermore, aluminum decreases t h e solu- b i l i t y of t h e in te rmeta l l i c phases i n @-Ti, and a s a r e s u l t , the boundaries of the two-phase (3 + S and f3 + y regions with t h e single-phase region of t h e p phase s h i f t toward a lower t o t a l content of i ron and chromium a s the content of aluminum i n t h e a l loys increases ( r e f s . 3 and 12) .

Hardness of the Alloys

The hardness of the alloys was measured on samples quenched from 1000 and 800' and annealed at 500.

The hardness of the alloys versus their composition is shown graphically in figure 3.

The maximum hardness is exhibited by alloys containing 2.5 wt percent (Fe -t ~ r ) of sections I and I11 and 5 wt percent (Fe + Cr) of section 11.

The most pronounced martensite decomposition of (3 grains is observed in -

these alloys, and this is what causes such an increase in hardness.

The hardest alloy was found to be the one containing 5 wt percent (Fe + Cr) of section 11. It is interesting to note that in the ternary system Ti-Fe-Cr, the maximum hardness in the quenched state is also displayed by alloys with the ratio Fe : Cr = 1 : 1 at a content of about 5 wt percent ( ~ e t- Cr) (ref. 12).

The minimum on the curves representing the dependence of the hardness on the composition corresponds to a content of 7.5 wt percent (Fe + ~ r ) in the alloys. These alloys have the structure of a fixed (3 solid solution. A further increase in the content of alloying components in the /3 phase promotes an increase in hardness.

At 800, the change in the hardness of the alloys as a function of composition follows the phase transformations in the system.

In the region of the a solid solution, the hardness rises with the sum of iron and chromium, reaching maximum values at the limit of maximum solubility of the alloying elements in a-Ti.

Fe + Cr, wt percent

Figure 3. Hardness of the alloys versus composition and temperature: a, section I, Fe:Cr = 3:l; b, section 11, Fe:Cr = 1:l; c, section 111, Fe: Cr = 1: 3; 1, alloys quenched from 1000~; 2, alloys quenched from 800'; 3, alloys annealed at 500~.

The appearance of t h e @ phase and increase i n i t s quant i ty cause a decrease i n the hardness of t h e a l loys . However, i n a l loys containing from 7.5 w t percent (Fe +- ~ r ) ( a s we l l a s on the llcomposition-hardnessl' curve a t 1 0 0 0 ~ ) ~ t h e hardness increases , s ince the @ p h a s e i s hardened by the alloying.

The curve representing t h e dependence of t h e hardness of t h e a l l o y on i t s composition a t 500' l i e s above an analogous curve f o r a l loys quenched from 800'. This i s explained by the presence i n t h e a l l o y s of in te rmeta l l i c phases resu l t ing from t h e eutec toid decomposition of t h e @ phase. The hardness of t h e a l loys a t 500 i n t h e region of a s o l i d so lu t ion va r ies as does t h e hardness a t 800.

I n t h e three-phase region, because of t h e increase i n the content of t h e in te rmeta l l i c compounds TiFe and TiCr2 i n t h e a l loys , t h e hardness should in-

crease. No such regular change i n hardness i s observed on curve 3 ( f i g . 3) . The a l loys of a l l t h e sec t ions containing about 1 0 w t percent (Fe + ~ r ) have minimum values of the hardness. This anomalous character of t h e dependence of t h e hardness on t h e composition can be a t t r i b u t e d e i t h e r t o an incomplete eu- t ec to id decomposition of the p phase o r t o t h e formation of t h e phase T i Al. 3 E l e c t r i c a l R e s i s t i v i t y

The e l e c t r i c a l r e s i s t i v i t y was studied on samples 5 mrn i n diameter quenched from 1000 and 800 and annealed f o r a long time a t 500.

Results of the measurements a re shown graphical ly i n f igure 4,

The phase transformations i n the a l loys a t 1 0 0 0 ~ a re ref lec ted by t h e curve representing t h e e l e c t r i c a l r e s i s t i v i t y versus the composition.

Figure 4. E l e c t r i c a l r e s i s t i v i t y of the a l loys versus composition and temperature: a , sec t ion I, Fe:Cr = 3 : l ; b, sec t ion 11, Fe:Cr = 1:l; c, sec t ion 111, Fe: C r = 1: 3; 1, a l loys quenched from 1 0 0 0 ~ ; 2, a l loys quenched from 8 0 0 ~ ; 3 a l loys anneded a t 500'.

I n the two-phase a + f3 region, the e l e c t r i c a l r e s i s t i v i t y

PHYSICAL Metallugy of Titanium by I.I. Kornilov

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