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DTIC ELECT F! ü£C 2 71984

E 3

TITLE: The Nature of the Critical and Strategic Materials Problem. Factors Affecting the Supply of Strategic Raw Materials with

Particular Reference to the Aerospace Manufacturing Industry. Measures for Materials Conservation in Aero-Engine Construction. Towards a Cycle without Loss: Cobalt in the Aircraft Industry. Gas Turbine Engine Design Considerations as Related to Alloys of

High Critical Element Content. Understanding the Roles of the Strategic Element Cobalt in Nickel

Base Superalloys. Oxide Dispersion Strengthened Alloys. Substitution and Conservation Technology for Chromium. Potential of Metal-Matrix Composites as Superalloy Substitutes. Manufacturing Developments to Reduce Strategic Materials Usage. Practical Implications of the Use of Alumlnlde Coatings for the

Corrosion Protection of Superalloys in Gas Turbines. Coatings for Fuel Economy or Materials Substitution. The Navy Program to Develop Replacements for Critical and Strategic

Materials. Ceramics as Subatitutas for Scarce Materials. New Developments in Materials Recycling by the US Bureau of Mines. Coating Developments to Restrict Strategic Materials Usage. Trace Elements In Superalloys and the Implications for Recycling. Trace Elements and Residual Elements in Superalloys. Recycling Conform Design.

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DT1C DEC 2 7 1984 3

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9-1

POTENTIAL OF NETAL-NATRIX COMPOSITES AS SUPERALI/OY SUBSTITUTES

by

N. McLean National Physical Laboratory

Teddlnqton, Mlddlaa*x TM11 OLW, UK

and

AD-P004 219

T. Khan Office National d'Ctudaa at da Recherche» Aaroapatlalas (ONERA)

BP72, 92)22 Chatlllon, Cadax, Franca

ABSTRACT

'The potential of metal-matrlx coaposltas aa qaa-turbina blada material« has largely been judged on the Increaaad taaparatura capabllltlaa they offer ovar tha atronqest current auperalloya. However, aavaral composite« that have bean rejected on thla basis are either independent of or have low concantrationa of critical alloying element». Consequently they should be reassessed as reserve material« aatching tha performance of exiatlng widely used »uperalloya that depend on strategically vulnerable conatltuents, A review of metal-ran»rix composites for high temperature applications will be made In order to identify Mterials that are inaensitive to tha supply of critical element».

An alternative approach might be to consider the potential of regenerating tha original creep performance of certian monocarbida reinforced nickel based composite» - such aa Cotac 744 developed at ONERA - after service exposure. In this context tha combination of perfectly elaatic fibrea in a craaping matrix would imply that high tamp» erature deformation of these «Mterials is almost completely recoverable. Hanca, ona should judge the potential of these materials in the light of total 1Ifa expectancy through both the processing and regeneration conditions rather than frofi their simple creep behaviour alone.

fro4 their all

INTRODUCTION

The principal «»tl vat ion for the development of high temperature composite materials for gas turbine applicationa appeara to have bean to exceed the temperature capable.tie« of the very strongest superalloys. The aim has been to produce materials with an addit- ional strengthening mechanism that remain» operative after tha usual hardening agent of nickel-base superalloys, vis y' precipitate, has dissolved in tha v-matrlx. Alloys have indeed been described that offer a clear technical advantage {^,2,3) over existing ■uperalloysi however, processing difficulties affecting tha economics of production have Inhibited the exploitation of these material«. VerSnyder (4) has expressed the optimis- tic view that cost-considerationa will only delay acceptance of theae materials until the 1990'si however, there must be a danger that tha advantages of these high strength composites will be superseded by developsMnts in other materials (eg single crystals, oxide-dispersion strengthened alloys, ceramics) .

The aim of this paper is to reaasass the potential of high temperature compoaltaa in the context of the themes of the present meeting. Firstly, they will be considered as direct substitutes which match but do not necessarily exceed the performance of existing materials tut which may offer significant advantages of reduced cost or reduced dependence on certain strategically vulnerable elements. Secondly, the response of composite ■Mterials to post-service rejuvenation procedures will be considered in order to assess the full potential service lives of components.

The emphaais will be on in-situ, rather than synthetic, composites since they are broadly compatible with existing investment caating and directional solidification technology and, consequently, are more likely to be accepted as direct substitutes for existing materiala. It may be neceasary to modify the processing conditions significantly (temperature gradient and solidification rate) and use different moulding materials In order to prevent »ould-(or core-lmalt Interactions. However, the basic aqulpaant and experience are available to allow commercial davalopawnt of in-aitu composites If an economic or strategic benefit warrants their exploitation.

CRITICAL METALS CONTENT

Analyses of import dependence of the US on critical metals have recently been published by Bradley (SI and by Natal Bulletin Monthly (6). These show that of tha usual constituent» of auperalloya more than 90% of cobalt« chromium, tantalum, manganeae and niobium originate from predominately Third Norld, South African and Eastern Bloc sources* consequently their supply is vulnerable to political and/or economic pressure. Tha

w MC

■Ituatlon is «van nor« saver« for the European Industry which ts dependent on virtually 100% of Its raw materials so that nickel, tltanlua, tunqsten, aolybdanum and vanadium are alao of strataqic isiportancet the supplies of these elesients, fro« ally nations, are perhaps politically assured but they «re still subject to economic pressures. It would clearly be politic to have alternative materials lea« dependent on certain critical metals, available for uae in important components in the «vent of disruption of supplies. It is unre««on«bl« to consider th« total elimination of all atrateqlc elements in « metallic component; rather we shall describe the «tructur« «nd properties of composites that hav« no or low concentrations of «pacific critical metals in relation to currant Material«. Their coaipoeition« are listed in Table 1.

CO-FREE ALLOYS

The mechanisms by which cobalt «trenqthen« nickel-base «uperalloy« hav« not been clearly established (7). Tien et al (7) have surveyed current evidence showing that the presence of cobalt can influence the volume fraction «nd «olvu« of th« y* precipitate, th« stsckina fault energy and the carbide chemistry which cumulatively lead to a large effect that makes cobalt an indispensible constituent of most advanced nickel-baa« «uperalloy«.

while th« benefit« of Co hav« been incorporated in the development of th« BK>«t advanced in-aitu composites, such «■ th« NITAC (2) «nd COTAC (1) series, some of the earlier version« were cobalt-free. However, the processing difficulties, low transverse ductilities and poor thermal fatigue resistance militate against any commercial exploita- tion of theae materials. Th« Y-T'-Cr3C2 alloy, developed at NPL (8), although not matching the high temperature strengths of the strongest in-«itu composites i« both cobalt- free and compare« favourably with many current alloys.

al Processing. Unlike many in-aitu composites which must be directionally solidified very slowly (< 10 BMh'M in v«ry high temperature gradient« (- 20 Kmm"1», Y-Y,-Cr3C2 can be successfully prepared «t high rates (up to 1000 sssh-'l «nd in relatively low temperature gradient«. This i« similar to th« c idltions used in the directional solidi- fication of superalloys. Th« alloy i« relatively insanaitive to the precis« compositions acceptable microstructur«« being obtained from a rang« of casts mad« to commercial specifications (Figur« 1|. It would be necessary, however, to develop new mould «nd cor« materials sine« there «r« significant interactions between the malt and the conventional silica-base shell moulds (Figure 2). However, «uch « development may alao be required to allow effective recycling of directionally solidified superalloys since silicon leached from the moulds can apparently weaken the longitudinal grain boundaries in direetionally solidified components prepared from revert superalloys.

^_ Th« density of 7.5 Mgm"^ is lower then that of most currant superalloys (similar to INI001 and the melting temperature of 1320*0 is «« high a« present ■uper«lloy«.

b( Phy«ic«l propertie« alloy« (iiimU

cl Oxidation/corro«ion r««i«t«nc«. Th« alloy ha« excellent cyclic oxidation reeistance assessed by laboratory thermogravimetrlc teat« and metallographic «xaminationt this ha« been confirmed in burner rig tests performed by Rolls-Royce Ltd at 1323 K in an •tmo«ph«r« containing 4 ppm NaCl. Th« results, shown «« depth of attack a« a function of time in Figure 3, compare favourably with previous data for typical ststor «nd rotor blade alloy« (C 1023 «nd HarMoo2 respectively). Indeed the uncoatad y-y'-CrjCj ha« similar oxidation resistance to aluminised superalloys.

In the more severe corrosion rig test for 300 h «t 8S0*C with fuel impurities of CIS «ulphur «nd SO ppm NaCl injected in the atmosphere there i« no detectable lost of section although IN713 i« severely affected in these conditions (Figure 4).

d| Wechanical Properties. The stress rupture data for y-Y'-CrjC] «re compared with thoae for currently available materials in Figure S. The absolute comparison of 1000 h rupture stresses, relevant to stator blade applications, show« « substantial benefit over current stator alloys. A density compensated comparison, of interest in relation to rotating components, shows that r-ir'-CrjCj Batches most blading alloys In the appro- priate atress range. In addition Y-T'-C^CJ has adequate impact, fatigue, thermal fatigue, notch sensitivity and transverse creep behaviour.

FERROUS-ALLOYS

Although the NATO nation« hav« • reaeonably assured supply of nickel, there would be both cost and technical advantages if iron-base alloys could replace nickel-baa« super- alloys for certain applications. As with y-y'-CrjC2, the processing conditions for in-aitu compo«it«« with M7C) reinforcement In HI, Co or Pe matrices are broadly coapatlblo with current commercial directional solidification practice, economic solidifi- cation rates of * 30 ■mh"1 being possible (»». A typical microstructur« of an (Fa, Crl- Cr7Cj in-«itu composite solidified at 30 mmh"' Is shown in Figure 6. Several studios of such iron-baa« alloy« hav« been reported (10,11,121 and th« currant statue of these materials is summarised below.

«I Physical Properties. The alloys have low tensities (> 7.3 Ngm'2) and melting

9*

te«p«ratur*« of 1200*C.

b) OKld«tlon/corro»lon rollt«nee. Iron based alloys contalnlnq aluminium and chromium toqethcr with minor addition« of actlv« elements (auch as yttrium, cerium or lanthanum) have outstandinq oxidation and corroalon resistance but arc relatively weak. Thar« has bean considerable success In Incraaalnq the creep strenqths of auch materials, by Incor- poratlnq carbide fibres, while retaining the excellent surface stability. The alloys with ferrltlc matrices tend to have better oxidation resistance than those with austen- Itlc matrices althouqh the latter have Improved creep resistance. Plqure 7 indicates the critical role that yttrium plays in Improvlnq the oxidation realstance.

c) Kechanlcal Properties. The stress rupture data are summarised In Plqure 8 as plots of the stress to cause rupture In 100 h aa a function of temperature. Information on current Iron- and nickel-base auperalloya are Included for comparison. The ferrltlc tn-sltu composite (NPL A) shows a very aubstantlal atrenqth advantaqe over the slnqle- phase FeCrAlV alloy which la flndlnq Increasing commercial application. However, the combination of atronq fibre and weak matrix would be expected to lead to poor thermal fatlque realstance. Conversion of the matrix to the austenltlc form has the dual effects of substantially Increaslnq the rupture strength (Plqure 8) and of qlvlnq better thermal fatlque performance. Two approaches have been taken to stabilizing the fee form of the matrix by substltutlnq nickel (11) (NPL B) or manqaneae (12) (UTRC) for Iron. Both lead to similar stress rupture properties with about three times the rupture strength of the ferrltlc alloy. More Importantly, they exceed the performances of advanced austentlc ferrous alloys (CRM-6D) and of some nickel-base superalloys (Nlmonle 80A, 90). Indeed with suitable density compensation these alloys are comparable to the strongest wrought superalloys (Nlmonle IIS).

CHROMIUM-FREE ALLOYS

Chromium Is, perhaps, the most vital conatltuent of auperalloya Imparting the required oxidation/corrosion resistance; however. It la alao among the most vulnerable to political or economic preasure. Rapid developments In coatlnq technology, the subject of other sessions at this meeting, give the hope of using chromium-free or low-chromium alloys as the main structure of a component which can then be protected by a corroalon resistant coating. Several studies have been made of ln-sltu composites In the Ni-Al-Mo (3,13,14) system which show some promise. These range from alloys having supcralloy-type y-y' matrices reinforced by a-Ho fibres (3,13) to y'-a (14) eutec- tlcs.

a) Processing. These alloys can usually be directlonally solidified at relatively high rates (up to 10 or 40 mmh'1» but this requires very high temperature gradients. Thus exploitation of these materials would require substantial modifications to the current commercial directional solidification equipment and procedures. Also the dependence on coatings would Introduce a substantial coat penalty.

b) Physical properties. This family of alloys has melting temperatures In excess of 13S0*C and densities of about 8.5 llgm-3.

c) Oxidation/corrosion resistance. The total absence of chromium means that these materials have very poor Intrinsic oxidation resistance. Some preliminary work has been carried out to determine their compatibility with coatings, but a great deal of further work would be required before such composite/coating systems could be exploited.

d) Nechanlcal properties, Y-Y'-CI ahowa a substantial temperature advantage In stress rupture testing over all available directionally solidified and single crystal materials (Figure 9). Harf (13) ha« demonstrated that suitable heat treatments can give the material adequate shear creep performance and, like most in-situ composites the fatigue properties are very good.

ECONOMIC CONSIDERATIONS

The basic raw material coats of the various alloys described above, at 1980 prices, are listed in Table 2 together with similar information for current and projected rival materials. There is a clear potential cost advantaqe in all of these materials if they can be shown to be technically acceptable. The most advanced ln-situ composites, such as COTAC 744 and NITAC 3-1ItA are presently much more expenslv«.However, one must consider the future usefulness of these materials both in terms of specific applications and the potential for savings through multiple service/rejuvenation cycles. Perhaps the most promising application of monocarbide reinforced euteetic« Is in small aeronautical engines (( 1S00 kMI. Here the use of advanced cooling technology is extremely difficult due to the small dimension« and thin sections of high pressure (HP) blades. It is not surprising that even the most modern small engines generally use solid uncooled blades. The turbine inlet temperatures (TIT) can therefore not be increased substantially aa in the caae of large gas turbine engines which benefit from the latest cooling technology. However, the present trend towards higher TXT for achieving a higher specific thrust will either require cooling of these already very thin airfoils or use of materials capable of sustsinlng higher temperatures. Belaygue (IS) has discussed and analysed in detail the various complications arising from an increase in TIT from 10S0* to laOO'C which

will npcessltate th Materials ar« uaed.

Introduction of cooled blades In these skall engines If conventional

Sine« om# advanced eutectlc composite» give a temperature gain of about 7S*C over presently available DS superalloys and about 50t: over current single crystal alloys, the use of uncooled eutectlc blades for such specialised applications may be viable. Example» of such components fre shown In Figure 11.

COMPONEWT RECYCLING

Another Interesting property of certain aonocarblde reinforced eutectlc» allows the original creep performance to be regenerated after service exposure. Therefore the over- all economic» of these basically expenalve Materials Must take Into account the life that can be achieved by Multiple service/regeneration cycles.

The creep deformation of composite» consisting of refractory fibres entrained In a relatively weak Matrix la quite different fro« that In superalloys. When the fibres and Matrix have widely different Melting temperature» as, for exaaple, NbC or TaC In nickel (eg In COTAC and NITAC alloys! It Is unlikely that both phaaes will creep. Indeed transMlsslon electron Microscopy shows no carbide dislocations after creep at teMperatures up to 1100'C. Rather, In service condition» the fibres, operating at very low homologous teMperatures, will deform elastlcally gradually off-loading atress from the Matrix to the fibres. The elastic deformation of the fibres Is recoverable by heat treatment. This effect waa first proposed and demonstrated by Khan et al (1) who designated It the 'length memory effect".

Specimen» of COTAC 744, whose Mlcrostructure la shown In Figure 12, were creep tested at various temperature» and stresses to about 1.2% strain In 200 to 300 hours. Previous work had shown that fibre fracture did not occur until about 1.3 to 1.61 strain. The »penmen» were re-heat treated without load (20 Mine at 1200*C, AC * 16 hours at S50*C/AC) and observed to contract to virtually their original lengths as documented In Table 3. On re-teatlng, the material had similar properties to the virgin Material. Consequently, the life expectancy of such Materials can, in principle, be substantially extended by repeated rejuvenating heat treatawnts and an effective evaluation of the potential of advanced in-aitu composites should take this into account. Clearly, the number of cycles that can be used in practice will depend on the do« I nance of other factors such as corrosion or fatigue crack growth.

Not all in-aitu composite» fully exhibit the length memory effect. For example, heat treatment of creep teated Y-Y'~Cr]C2 result» in recovery of only part of the creep ■train, the extent of recovery being greateat at low teMperatures (Figure 101. This ia probably due to the relatively high homologous teaperature of C^C], particularly at 82i*C, resulting in creep of the fibrea.

An important consequence of the stress carrying capacity of elastic fibres is that established extrapolation procedure», such as Larson-Nlllar plots, that have evolved for conventional engineering alloys, will always underestlstata the long tens properties of in-sltu composite». In a recent theoretical treataent, McLean (16) has shown that for elastic fibres in a creeping Matrix there ist

aI no steady state deformation

bl a decreasing creep rate that approaches sero when all of the atreaa ia carried by the fibres

c| a break-down in the linear relationship between log (atress) and log (creep rate at 1% extension) or log (tiMe to It extension) at low stresses where the creep perform- ance ia Much better than indicated by data extrapolation.

CONCLUSIONS

Although in-aitu coMpoaltes have »o far failed to Meet the coablned econoaic and technical targets for preaier coaponenta auch aa HP1 turbine blades, at leaat aoae alloy» appear to offer less direct benefits that could be of iaportance in the event of disrup- tions of supplies of critical aetals

a) Y-r'-CrjC, is • cobalt free alloy with good oxidation resistance and coaparable strength Co aost existing superalloya.

b) Several iron-ba. i coaposites with N7C3 relnforcsasnt having no or little nickel, coablne good oxidation resistance with the creep perforaanca of many nickel-base superalloys.

c) Y-Tf'-a Is a high strength chroalua-frea alloy that aay have usas in coablnatlon with protective coatings.

In addition, the potential of the aost advanced coaposites, such as N1TAC3-116A and

'

■iV.

9-5

COTAC 744 (or their derivativ««)( may not b« fully appreciated for th« following reaaonss

1) TliM-d«pendent deformation In alloy« with hlqhly refractory fibre» 1« totally recover- able ao that the original properties can be r«-««tabll«h«d «everal tin«« by heat treat- ment .

21 Extrapolation of short-term data always provide» a peaslmlatlc eattmate of th« long term performance of ln-«ltu compoalt«a.

)) Introduction of cooled HP blades In «mall «nqln«« (< 1S00 kW) may not be a practical way of Increasing the overall «nqln« efficiency and consequently the hlqher temperature capabllltlea of some eutectlc composites may offer an attractive solution.

REFERENCES

1. T. KHAN, J.F. STOHR and H. BIBRING In Superalloy« 1980, pp S31-S40, edited by J.K. Tien et al, American Society of Metal«, Metal» Park, OH 1980.

2. CA. BRUCH, H.W. HARRISON, N.F.X. GIGLIOTTI, M.F. HENRY, R.C. HAUBERT and C.H. Gay, Proc, of Conference 'In-Sltu Composites III, pp 2S8-267, edited by J.L. Malter et al. Ginn and Co, Lexington, Mas«., 1979.

1. H.F. HENRY and N.R. JACKSON, NASA report CR-159416 (1979).

4. F.L. VERSNYDER In 'High Temperature Alloy« for Ga« Turbines 1982*. pp 1-50, edited by R. Brunetaud et al, Reldel Publishing Co., Dordrecht, Holland (1982).

5. E.F. BRADLEY, 'Critical Metal» - Conservation, Recycling and Substitution', AGARO discussion paper, 1982.

6. Metal Bulletin Monthly, 'How Strategic are Strategic Metal«?* pp 43-60, August 1982.

7. J.K. TIEN and R.N. JARRETT, In 'High Temperature Alloy« for Ga« Turbines 1982', pp 423-446, edited G.R. Brunetaud et al, Reldel Publishing Co., Dordrecht, Holland (1982).

6. E. BULLOCK, P.N. QUESTED and M. NcLEAN, Proc. of Conference 'In-Sltu Composite» III*, pp 420-430, edited by J.L. Malter et al. Ginn and Co., Lexington, Mas« (1979).

9. V.M. HILDEBRANDT and P.R. SAHM, J. Mater. Scl., n, 1031 (197S).

10. J. VAN DEN BOOMGAARD and A.M.J.G. VAN RUN, Proc. of Conf. on In-Sltu Composites, p 161, edited by F.D. Lemkey and E.R. Thompson, NMAB Report 308-11, National Academy of Science«, 1973.

P.N. QUESTED, D.E. MILES and M. McLEAN, Metal« Technology, 7, pp 433-440 (1980).

F.D. LEMKEY, E.R. THOMPSON, J.C. SCHUSTER and H. NOWOTNY, Proc. of Conf. 'In-Sltu Composite« IV*, pp 31-SO, edited by F.D. Lemkey «t al. North Holland, NY (1983).

F.H. HARF, Proc. of Conference 'In-Sltu Componltes III*, pp 399-409, edited by J.L. Walter et al, Glnn and Co, Lexington, Mas« 1979.

D.D. PEARSON, Proc. of Conference "In-Sltu Composites lit', pp 389-398, edited by J.L. Malter et al, Glnn and Co, Lexington, Mass 1979.

P. BELAYCUE. AGARD Conference Proceeding« 229, High Temperature Problem« In Ga« Turbine Engine«, 19''7.

M. McLEAN, -Dlrectlonally Solidified Materials for High Temperature Service", Book 296, The Metal« Society. London, 1983.

•J-h

Table 1. Compo«ltIon» of ln-»ltu composite« Iwtl)

Alloy Nl Co Cr Al C r« No M Ta Nb Hn y V 1

Re

•1 y-Y'-CrjCj bal - 12.3 6 9 1.8 - - - - - - 0 5 - - |

b) Pe-base

NPL A (farrltlc) NPL B (austanttlcl UTRC (austenltlc

15.0 - 33 2 18.2 20.0

3 2 3.2

2.6 2.6 3.2

bal bal bal :

- - : 10 0

0 8 0 8

- -

c( y-y'-a Y'-a

bal bal - -

6.0 2.2

- - 32 0 21 0

- 35.9

- -

- - - |

dl COTAC 744 NITAC 14B

bal bal

10 3.7

4 1 9

6 6.S

0.47 0.24

- 2 10 8.2

3.8 - 4 2 6.3

Allov

Table 2. Raw Material coats of in-altu compoilte» and conventional high tenperature alloys. (1980) prices.

Cost 6/Kq

Y-Y'-CrjCj 5.3

Pe-base

NPL A ' NPL B ÜTRC

1.5 -

Y-Y'-a 9.5

Y'-a 53.7

COTAC Hi I* 12.5

NITAC 141 !• >20

IN 738LC IN939 IN 100 Mar N002 X-40

11.3 14.0 11.4 16.3 25.2

4.0

ln-altu composites

■uperalloys

■

* The low yield of COTAC and NITAC alloy components du« to Slow processing rates and the small nuatber of blades produced per cycle may lead to a substantial premlun tn the processing stage -iver the cost of DS and single crystal superalloy castings.

Table 3. Improvement In stress rupture life of COTAC 744 after repetitive heat treatments

Creep teat conditions

initial

Gauge

lat creep

length

Heat treat

2nd creep

Heat treat

Tims to rupture, h

cumulative un-interrupted Temp Stress | *C NPa

•50 400 900 310 1000 220

30.02 39. «• 30.00

30.40 30.36 30.36

30.06 30.08 30.0«

30.43 30.35

30.10 30.01

1040 700 1303 700 303 300

.„

47

'

lit« ■" . ■ *;■ ." v . '-

Figure 1. Micrographs of la) longitudinal and (bl tranaverae aectlona of f-t'-CriCj dlractlonally aolldlfled at 300 mm h'1 In a temperature gradient of - 13 Kaa'l.

r.

20 pm

10 M»«

Figure 2. Tranaverae aectlona of Y-Y'-Cr3C2 dlractlonally solidified In (a) a convm- tlor.al alllca-bound shall mould and lb» racryatalllsad alumina.

Figure 3. Depth of penetration of corrosion products during burner rig taata at 1323 R with 4 ppm salt.

•)*

1 mm

Flqur« 4. Co«p«rl»on of ••ctlon* of (at T-T,-Cr]C2 and (b) IN71JLC after burner rlq taata at B50*C for 300 h.

SOOr

■ ,

Nimonic

Ttmp*rotur**C

riqur« 6. Straaaea to cauaa ruptura In 100h aa a function of taaparatur« for farroua ln-altu coapoattaa. Data for conventional Iron- and nlckal-baaa alloys ara Included for eoaparlaon.

Plqure i. Mlcrocirapha of (a) lonqltudlnal and (bl tranavaraa aactlona of the FeCrAlY-CrTCi In-aitu coapoalta (NPL A) retrAix-try«.j in-axtu coaipoi dlrectionaily solidified at 300 mmh -1

Tim», h

riqure 7. Coaiparatlve «Might chanqaa during cyclic oxidation taatlnq of farroua ln-altu coMpoaltea.

r

- 99

O

a 3

C o 8

800 900

T^mp^rolure'C

WO noo

E z

50

«0

30

I

"? 10

I ISO MPo • Sgcm' (rotor tlrM«)

700 M0

C0TAC 7U

\ \ 'CMS 12

MorMIOOOS '-'-Cr|C,

MO

T#mp»folurt»C

1000 "00

Figur« S. Strotsoa to caua« rupture In 1000 h as a function of toaporatur« for Y-v'-CriCi. Data ar« ahown for rival auparallova and ln-altu ooapoaltoa for coa^arlaon (a) absolut« atraaaaa (bl donalty coaponsatad atraaaaa.

«10

1100

o 900

no

TOO

r couc 74*

CMS.2 l-W h Mor MooJ

Mar Moo2 OS cc

[ .* • WaxxXioy *• o t o

1 *

j 11

t

* I

i £1

1 V

i a

Plqure '. Potential rotor op«ratlnq temparatur« for .-.'-i In relation to rival alloys.

? i t E t o c Ö

36 15 34

15fs. U 13 12 11 10 09 06

- - „- w Creep le»le<J o« 625»C

07

'X- -K Tetled o! TSO'C

- X ». Tested at 650*0 i

Time at 1l0O*C.h

200

Figure 10. Change in length with tine of creep tpeclmens of Y~Y'~Cr3C2 during unloaded heat treatment at 1100*C after different prior teat conditions.

•

it*»'- •.

ätt.

Figure 11. Finished uncooled blade« of the COTAC 74 in-«ltu coaipoalte.

^ s

Figure 12. Typical ■lerostrueture of a V-Y' »onocarbldo reinforced COTAC eutectlc (transverse section of COTAC 74 showing NbC fibres e^>edded In a Y-Y* ■atrlx).