Fatigue, Fretting Fatigue and Corrosion Characteristics

Fatigue, Fretting Fatigue and Corrosion Characteristics

of Biocompatible Beta Type Titanium Alloy Conducted

with Various Thermo-Mechanical Treatments

Toshikazu Akahori1, Mitsuo Niinomi1, Hisao Fukui2 and Akihiro Suzuki3

1Department of Production Systems Engineering, Toyohashi University of Technology, Toyohashi 441-8580, Japan2Department of Dental Materials Science, School of Dentistry, Aichi-Gakuin University, Nagoya 464-8650, Japan3Titanium Division, Daido Steel Co. Ltd, Tokyo 105-8403, Japan

Plain and fretting fatigue properties of type titanium alloy, Ti-29Nb-13Ta-4.6Zr, underwent various thermo-mechanical treatments wereinvestigated in order to judge its potential for biomedical applications. Ti-29Nb-13Ta-4.6Zr aged directly at 723K for 259.2 ks after cold rollingshows the greatest fatigue strength in both low cycle fatigue life and high cycle fatigue life regions, and the fatigue limit, which is around770MPa, is nearly equal to that of hot-rolled Ti-6Al-4V ELI conducted with aging, which is one of representative type titanium alloys forbiomedical applications. Fretting fatigue strength tends in proportion to Youngs modulus. Fretting fatigue limits of the forged bar of Ti-29Nb-13Ta-4.6Zr conducted with solution treatment, and aging at 723K after solution treatment are around two thirds and a half of plain fatigue limits,respectively, and those are around 180MPa and 285MPa, respectively. Passive current densities of the plate of Ti-29Nb-13Ta-4.6Zr conductedwith a multi-step-thermo-mechanical treatment, where the cold rolling and solution treatment are repeated 4 times, in 0.5%HCl and Ringerssolutions are much smaller than that of Ti-29Nb-13Ta-4.6Zr conducted with general thermo-mechanical treatment, and the values are a littlesmaller than those of forged Ti-15Mo-5Zr-3Al conducted with annealing and hot rolled Ti-6Al-4V ELI conducted with aging.

(Received December 3, 2003; Accepted February 23, 2004)

Keywords: titanium-29mass%niobium-13mass%tantalum-4.6mass%zirconium, tensile properties, plain and fretting fatigue properties,

corrosion resistance, biomedical application

1. Introduction

Co-Cr alloy and 316L stainless steel have been mainlyused for biomedical applications because of their excellentcombination of strength and corrosion resistance.1) Toxicityand allergic problems of alloying elements and high Youngsmodulus of these metallic biomaterials have been, however,pointed out recently.2,3) Titanium and its alloys, in particular, type titanium alloys such as Ti-6Al-4V ELI and Ti-6Al-7Nb have been, therefore, used as the most attractivebiocompatible metallic materials due to their excellentcombination of mechanical properties, corrosion resistanceand biocompatibility. Their Youngs moduli are, however,still greater comparing with that of the cortical bone. typetitanium alloys such as Ti-13Nb-13Zr and Ti-15Mo-5Zr-3Alwith low Youngs modulus and greater strength have been,therefore, developed for biomedical applications. A new type titanium alloy composed of non-toxic and non-allergicelements like Nb, Ta, and Zr, Ti-29Nb-13Ta-4.6Zr,46) hasbeen recently developed in order to achieve lower Youngsmodulus and excellent mechanical performance.

Implant instrumentations like bone plates, screws andnails, artificial spines, and artificial femoral and hip joints areused under fatigue conditions and sometimes failed due tomonotonic load, fatigue and corrosion fatigue. Mechanicalperformance, in particular, tensile, and plain and frettingfatigue performances are very important factors for titaniumalloys for biomedical applications. There are a few papers onfatigue and corrosion resistance of type titanium alloys forbiomedical applications although there are many papers onthose of type titanium alloys such as Ti-6Al-4V ELIand Ti-6Al-7Nb for biomedical applications.710)

Plain and fretting fatigue performances of an alloy areimportant mechanical properties to confirm the reliability as

metallic biomaterials. It is well-known that for titaniumalloys these properties are changed according to the micro-structures obtained by heat treatments or thermo-mechanicaltreatments. Therefore, tensile, and plain and fretting fatigueproperties of newly developed type titanium alloy, Ti-29Nb-13Ta-4.6Zr, conducted with various thermo-mechan-ical treatments were investigated in this study. The basiccorrosion characteristics of Ti-29Nb-13Ta-4.6Zr were alsoinvestigated.

2. Experimental Procedures

The materials used in this study were forged bars of Ti-29Nb-13Ta-4.6Zr (Nb: 29.2, Ta: 12.3, Zr: 4.4, O: 0.10, H:

mechanical treatment in Ar gas atmosphere followed by WQ,where solution treatment at 1063K for 3.6 ks was succes-sively done after each cold rolling up to a reduction ratio of87.5%, and finally aged at 673K for 259.2 ks in Ar gasatmosphere followed by WQ, in order to improve thecorrosion resistance. TNTZd20 was conducted with multi-step-thermo-mechanical treatment, and it is designated asTNTZmulti here in after.

The constitutional phases of TNTZ conducted with variousthermo-mechanical treatments were examined through an X-ray diffraction (XRD) analysis and observations using ascanning electron microscopy (SEM) with an energy dis-persive X-ray spectroscopy (EDX) and a transmissionelectron microscopy (TEM). XRD analysis was carried outusing a Cu target with an accelerating voltage of 40 kV and atube current of 20mA. SEM and TEM observations werecarried out with an acceleration voltage of 20 kV and 200 kV,respectively.

Smooth plate specimens with a cross section of3:0 1:5mm2 and a gage length of 13mm and cylindricalspecimens with a diameter of 5.0mm and a gage length of24mm for tensile and plain fatigue tests, and smooth platespecimens with a cross section of 3:0 1:5mm2 and a lengthof 40mm and cylindrical specimens with a diameter of10mm and a thickness of 4mm for measuring Youngsmodulus and corrosion characteristics were machined formthe heat-treated plates and bars with their longitudinaldirections parallel to the rolling direction. The surface ofspecimen for measuring corrosion characteristics was fullycovered with epoxy resin except for an area of 7.85mm2 forexposing to each solution, which will be described below.Fretting fatigue specimens have double square bodies with athickness of 4.0mm and a length of 20mm. Bridge type padswith a span length of 10mm for fretting fatigue test made ofthe same materials as that for the fretting fatigue specimenswere used.

Tensile tests were carried out on the tensile specimensfinished as stated above using an Instron type machine withan initial cross-head speed of 8:33 106 m/s in air at295K. The strain was measured using a clip gage attached tothe gage-length area of the specimen and a foil strain gageattached directly to the gage section of the specimen.

Moduli of elasticity on the specimens for measuringmodulus of elasticity finished as stated above were measuredusing a resonance method.

Plain and fretting fatigue tests were carried out on the plainand fretting fatigue specimens using an electro-servo-hydraulic machine. Each fatigue test was performed at afrequency of 10Hz with a stress ratio, R 0:1, under thetension-tension mode in air at 295K and Ringers solution at310K. The contact pressure was maintained at 153MPa. Themaximum cyclic stress, at which the specimen was stillunfailed at 107 cycles, was defined as the plain or frettingfatigue limit in this study.

Corrosion characteristics was evaluated by anodic polar-ization test in 5%HCl and Ringers solutions at a temperatureof 295K which were deaerated by high purity N gases at aflow rate of 200mL/min for 1.8 ks in order to reduce oxygencontent. The specimens were subjected to cathodic treatmentat0:9Vwith referring to saturated calomel electrode (SCE)

for 900 s to remove oxide film formed on its surface. After thenatural electrode potential became stable, anodic polarizationtests were conducted at a sweep rate of 20mV/min from thenatural electrode potential to 2.5V.

3. Results and Discussion

3.1 MicrostructureFigure 1 shows XRD profiles of TNTZST, TNTCR, and

TNTZST and TNTCR conducted with various heat treatments.XRD profiles show no precipitation in phase of TNTZSTand TNTZCR. XRD profiles reveal that and ! phases, and phase are precipitated in TNTZST aged at 673K and 723K,respectively. While TNTZST aged at 598K has ! phase. InTNTZCR aged at 673K and 723K, phase mainlyprecipitates in phase, and the peak intensity of phase ismuch larger than that of TNTZST. The precipitated phase inTNTZCR aged at 598K is difficult to confirm because allpeaks of and ! phases overlap each other with background.

3.2 Tensile propertiesTensile properties of TNTZST, TNTZCR, and TNTZST and

TNTZCR conducted with various heat treatments are shownin Fig. 2 with those of hot-rolled Ti-6Al-4V ELI conductedwith aging11) and forged Ti-15Mo-5Zr-3Al conducted withannealing12) as comparison. The tensile strength, 0.2% proofstress and elongation of TNTZCR are 830MPa, 755MPa and15.2% on the average, respectively. The tensile strength and0.2% proof stress of TNTZCR are around 150MPa greaterthan those of TNTZST, which has 650MPa and 600MP,respectively. On the other hand, the elongation of TNTZCR isa half of TNTZST. The tensile strength and 0.2% proof stressof all aged TNTZST and TNTZCR are more than 1.5 timesgreater than that of TNTZST and TNTZCR. In particular, theelongation of TNTZST and TNTZCR aged at 598K, whichhave super fine ! phase or phase, are very poor though thetensile strength and 0.2% proof stress increase remarkably ascompared with those of TNTZST and TNTZCR. On the otherhand, the tensile strength and 0.2% proof stress of TNTZSTand TNTZCR aged at 673K and 723K, which mainly have phase, tends to be 50MPa to 200MPa smaller than those ofTNTZST and TNTZCR aged at 598K.

Tensile strength and 0.2% proof stress of TNTZST aged at598K and TNTZCR aged at 723K are nearly equal to those ofhot-rolled Ti-6Al-4V ELI conducted with aging after solutiontreatment, and forged Ti-15Mo-5Zr-3Al conducted withannealing, and each elongation is over 20%.

3.3 Youngs modulusYoungs moduli of TNTZST, TNTZCR, and TNTZST and

TNTZCR conducted with various heat treatments are shownin Fig. 3 with those of hot-rolled Ti-6Al-4V ELI conductedwith aging13) and forged Ti-15Mo-5Zr-3Al conducted withannealing.12) The Youngs modulus of TNTZST, which isaround 63GPa, is pretty similar to that of TNTZCR. TheYoungs modului of forged Ti-15Mo-5Zr-3Al conductedwith annealing and hot-rolled Ti-6Al-4V ELI conducted withaging are around 90GPa and 110GPa, respectively. TheYoungs moduli of TNTZST and TNTZCR are a half of that ofhot-rolled Ti-6Al-4V ELI conducted with aging, and is twice

Fatigue and Corrosion Characteristics of New Beta Type Titanium Alloy 1541

as large as that of compact bone.14) The Youngs moduli ofaged TNTZST and TNTZCR tend to increase significantlywith increasing aging temperature. This trend is almostsimilar to that of tensile strength and 0.2% proof stress. TheYoungs moduli of all aged TNTZST and TNTZCR are 20GPa

Ti-

15M

o-5Z

r-3A

l

0

5

10

15

20

25

30

0

200

400

600

800

1000

1200

Ten

sile

Str

engt

h,

B /

MP

a0.

2 %

Pro

of S

tres

s,

0.2 / M

Pa

Elo

ngat

ion

(%)

BElongation

0.2

TN

TZ

ST A

ged

at 5

98 K

TN

TZ

ST

TN

TZ

ST A

ged

at 6

73 K

TN

TZ

ST A

ged

at 7

23 K

0

5

10

15

20

25

30

35

40

0

200

400

600

800

1000

1200

1400

1600

Ten

sile

Str

engt

h,

B /

MP

a0.

2 %

Pro

of S

tres

s,

0.2 / M

Pa

Elo

ngat

ion

(%)

TN

TZ

CR

TN

TZ

CR

Age

d at

598

K

TN

TZ

CR

Age

d at

673

K

TN

TZ

CR

Age

d at

723

K

Ti-

6Al-

4VE

LI

Fig. 2 Tensile properties of TNTZST, TNTZCR, and TNTZST and TNTZCRconducted with aging at 598K, 673K and 723K for 259.2 ks, hot-rolled

Ti-6Al-4V ELI conducted with aging, and forged Ti-15Mo-5Zr-3Al

conducted annealing.

TNTZST

TNTZSTAged at 673K

TNTZSTAged at 598K

TNTZSTAged at 723K

30 40 50 60 70 80

Diffraction angle, 2 /(180-1)rad

(3

0 . 1)

(2

20)

(1

0 . 0)

(1

0 . 1)

(0

0 . 1)

(1

0 . 2)

(1

1 . 0)

(0

0 . 2)

(2

00)

(1

10)

(2

11)

TNTZCR

TNTZCRAged at 673K

TNTZCRAged at 598K

TNTZCRAged at 723K

30 40 50 60 70 80

(1

10)

(2

00)

(2

11)

(2

20)

(1

0 . 0)

(1

0 . 1)

(0

0 . 2)

(1

0 . 2)

(1

1 . 0)

Diffraction angle, 2 /(180-1)rad

(a) (b)In

tens

ity

Inte

nsit

y

Fig. 1 X-ray diffraction profiles of TNTZST, TNTZCR, and TNTZST and TNTZCR conducted with aging at 598K, 673K and 723K for

259.2 ks.

0

20

40

60

80

100

120

You

ngs

Mod

ulus

, E /

GP

a

TN

TZ

ST A

ged

at 5

98 K

TN

TZ

ST

TN

TZ

ST A

ged

at 6

73 K

TN

TZ

ST A

ged

at 7

23 K

Ti-

6Al-

4V E

LI

0

20

40

60

80

100

120

You

ngs

Mod

ulus

, E /

GP

a

TN

TZ

CR

TN

TZ

CR

Age

d at

598

K

TN

TZ

CR

Age

d at

673

K

TN

TZ

CR

Age

d at

723

K

Ti-

15M

o-5Z

r-3A

l

Fig. 3 Youngs moduli of TNTZST, TNTZCR, and TNTZST and TNTZCRconducted with aging at 598K, 673K and 723K for 259.2 ks, hot-rolled

Ti-6Al-4V ELI conducted with aging, and forged Ti-15Mo-5Zr-3Al

conducted with annealing.

1542 T. Akahori, M. Niinomi, H. Fukui and A. Suzuki

to 40GPa greater than those of TNTZST and TNTZCR. TheYoungs moduli of TNTZST and TNTZCR aged at 723K arerelatively smaller than that of hot-rolled Ti-6Al-4V ELI andforged Ti-15Mo-5Zr-3Al. The Youngs moduli of TNTZSTand TNTZCR aged at 723K are smaller than those of TNTZSTand TNTZCR aged at 598K and 673K because phase isprecipitated. Therefore, Youngs modulus of TNTZ increaseswith increasing volume fraction of ! phase.

3.4 Fatigue properties3.4.1 Plain fatigue strength of TNTZST, TNTZCR, and

TNTZST and TNTZCR conducted with variousaging in air

Maximum cyclic stress-fatigue life (the number of cyclesto failure) curves, that is, S-N curves, obtained from plainfatigue tests on TNTZST and TNTZCR conducted withvarious heat treatments in air are shown in Fig. 4 withranges of fatigue limits, which are maximum cyclic stressesat which the specimens are not failed at 107 cycles, of hot-rolled and cast Ti-6Al-4V ELI,11) and Ti-6Al-7Nb.11)

The plain fatigue strength of TNTZST and TNTZCR aged attemperatures between 593K and 723K increases remarkablyas compared with that of TNTZST and TNTZCR in both lowcycle fatigue life (less than 105 cycles) and high cycle fatiguelife (more than 105 cycles) regions. The plain fatigue strengthof aged TNTZST and TNTZCR rise proportionally withincreasing aging temperature. The plain fatigue limit ofTNTZCR aged at 723K is the greatest among the other agedTNTZST and TNTZCR, and it is around 780MPa. The plain

fatigue limit of TNTZCR aged at 723K is about twice of thatof TNTZCR. The improvement in plain fatigue strength ofTNTZCR aged at 723K is resulted from increasing tensilestrength due to homogenously precipitated fine phasewhich leads to increase crack initiation resistance, andrelatively greater elongation which improves small fatiguecrack propagation resistance. The trend of increment of plainfatigue strength of aged TNTZST is nearly equal to that ofaged TNTZCR. The plain fatigue limit of TNTZST aged at723K is around 680MPa. The plain fatigue limits ofTNTZCR aged at 673K and 723K are much greater thanthose of Ti-6Al-7Nb with equiaxed and Widmanstatten structures, and are nearly equal to that of Ti-6Al-4V ELI withequiaxed structure, which has around 800MPa.

Fatigue fracture surface of TNTZCR aged at 723K in highcycle fatigue life region is shown in Fig. 5. The crackinitiation site is at the surface of specimen as shown in Fig.5(a). The main crack propagates vertical to the stress axis,and then propagates parallel to the stress axis with forming anumber of striations with a width of around 185 nm as shownin Figs. 5(b) and (c). This is due to the strong texture withcrystals aligned normal to the rolling direction. Then, thecrack deflects cyclically in stable fatigue crack propagationarea, which results in increasing fatigue crack propagationlife. Therefore, it is considered that the stable crackpropagation area composed of striations in TNTZCR aged at673K and 723K is much greater than that in the otherTNTZST or TNTZCR.

Fatigue crack of TNTZST aged at 598K initiated at

300

400

500

600

700

800

900M

axim

um C

yclic

Str

ess,

m

ax/M

Pa

Number of Cycles to Failure, Nf

105 106 107104103 108* : Hot Rolled Plate

**: Cast Bar

TNTZST

TNTZST aged at 598 K



TNTZCR aged at 598 K


TNTZCR


Ti-6Al-7Nb** (Coarse Acicular )

Ti-6Al-4V ELI**(Coarse Acicular )

Ti-6Al-7Nb* (Acicular )

Ti-6Al-4V ELI* (Acicular )

Ti-6Al-7Nb* (Equiaxed )

Ti-6Al-4V ELI* (Equiaxed )

Fatigue Limit Range of Ti-6Al-4V ELI

Fatigue Limit Rangeof Ti-6Al-7Nb

Fig. 4 S-N curves of TNTZST, TNTZCR, and TNTZST and TNTZCR conducted with aging at 598K, 673K and 723K for 259.2 ks with

those of Ti-6Al-4V ELI and Ti-6Al-7Nb in air.


subsurface due to slip plane decohesion, which initiated near! phase because ! phases in phase were super fine and theirvolume fraction was relatively greater in high cycle fatiguelife region. Therefore, slip may not move actively in or near! phase, which leads to the dislocation accumulation near the! phases. However, further investigation is needed to makesure on this point. In this case, the remarkable change infatigue life depending on the crack initiation site may notoccur.3.4.2 Plain fatigue strength of TNTZST and aged

TNTZST in Ringers solutionS-N curves obtained from fretting fatigue tests on TNTZST

and TNTZST aged at 673K in Ringers are shown in Fig. 6with those of TNTZST and TNTZST aged at 673K in airalready shown in Fig. 4. The fatigue strength in Ringerssolution is equal to that in air for both as-solutionized andaged conditions. Therefore, the fatigue strength of TNTZ isnot degraded in Ringes solution.

50 mCrack Initiation Site

(a)

(b)

250 nm

Striation

(c)5 m(b)

(c)

Fig. 5 SEM fractographs of (a) crack initiation site, and (b) and (c) stable crack propagation area of TNTZCR aged at 723K for 259.2 ks.

300

400

500

600

700

800

105 106 107104

Max

imum

Cyc

lic s

tres

s,

max

/MP

a


Solid Symbol: in Air

Open Symbol: in Ringers Solution

TNTZST

TNTZSTaged at 673 K

Fig. 6 S-N curves of TNTZST and TNTZST aged at 673K for 259.2 ks in

air and Ringers solution.


3.4.3 Plain and fretting fatigue strength of TNTZd12 andaged TNTZd12 in air

S-N curves obtained from plain and fretting fatigue tests onTNTZd12 and aged TNTZd12 in air are shown in Fig. 7. Theplain fatigue limits of TNTZd12 and TNTZd12 aged at 723Kfor 172.8 ks after solution treatment were around 330MPaand 715MPa, respectively. The fretting fatigue strength ofTNTZd12 conducted with solution treatment is around twothirds of its plain fatigue strength in both low cycle fatiguelife and high cycle fatigue life regions. The fretting fatiguelimit of TNTZd12 is around 180MPa. On the other hand, thefatigue limit of TNTZd12 aged at 723K for 172.8 ks falls toaround 40% of its plain fatigue limit, that is around 285MPa.The difference in fretting fatigue limits between TNTZd12and TNTZd12 aged at 723K for 172.8 ks are around 120MPaalthough that in plain fatigue is around 385MPa.

In fretting fatigue in air, the ratio of fretted damage, Pf=Ff ,where Pf and Ff are the plain fatigue limit and the fretting

fatigue limit, respectively increases with increasing elasticmodulus as shown in Fig. 8, where relationship betweenPf=Ff and Youngs modulus of forged Ti-15Mo-5Zr-3Alconducted with annealing12) is also shown for comparison.Pf=Ff increases proportionally with increasing Youngsmodulus. Fretting fatigue crack generally initiates at theboundary between slip and stick region on the specimensurface, where maximum frictional force occurred.1517)

There is a possibility for cyclic action of the pad to berestricted in TNTZ especially in high contact pressure likethe case in this study because of lower modulus of elasticityas schematically shown in Fig. 9. The fretting area of TNTZin high contact pressure is for the most part dominated bystick region. The fretting damage of low rigidity metallicmaterial may decrease with increasing contact pressure.3.4.4 Plain and fretting fatigue strength of TNTZd12 in

Ringers solutionS-N curves obtained from plain and fretting fatigue tests on

TNTZd12 in air and Ringers solution are shown in Fig. 10.The plain fatigue strength of TNTZd12 in Ringers solution isnearly equal to that in air. The same trends can be seen inTNTZST and TNTZST aged at 673K as already shown inFig. 7. However, the fretting fatigue strength of TNTZd12conducted with ST in Ringers solution is greater than that in

0

200

400

600

800

1000

104 105 106 107


Max

imum

Cyc

lic S

tres

s,

max

/MP

a

TNTZd12

TNTZd12 Aged at 673 K

Solid Symbol: Plain Fatigue

Open Symbol: Fretting Fatigue

Fig. 7 S-N curves of forged TNTZd12 and TNTZd12 conducted with aging

at 673K 259.2 ks obtained from plain fatigue and fretting fatigue tests in

air.

TNTZd12

TNTZd12 Aged at 723 K

Ti-15Mo-5Zr-3AlConducted withAnnealing

Pf / Ff

1.0 1.5 2.0 2.5 3.0 3.5 4.050

60

70

80

90

Mod

ulus

of

Ela

stic

ity

/ GP

a

100

Fretting DamageLow High

Fig. 8 Relationships between the ratio of fretting damage, Pf=Ff , andmodulus of elasticity of TNTZd12, TNTZd12 conducted with aging at 723K

172.8 ks and forged Ti-15Mo-5Zr-3Al conducted with annealing. Pf and

Ff indicate plain fatigue limit and fretting fatigue limit, respectively.

Fretting Pad

Fatigue Specimen

Stick Region

Slip Region

Slip Region

Fretting Pad

Fatigue SpecimenDif

fere

nce

in G

rade

Stick Region

Small Slip Region or Non-Slop Region

(b) High Contact Pressure(a) Low Contact Pressure

Fig. 9 Schematic drawing of relationship between fretting pad and

specimen in material with low Youngs modulus during fretting fatigue

test at (a) low and (b) high contact pressure.


Max

imum

Cyc

lic S

tres

s,

max

/MP

a

0

100

200

300

400

500

600

104 105 106 107

Solid Symbol: in Air

Open Symbol: in Ringers Solution

Plain Fatigue

Fretting Fatigue

Fig. 10 S-N curves of TNTZd12 obtained from plain fatigue and fretting

fatigue tests in air and Ringers solution.


air in low cycle fatigue life region, but a little lower than thatin air in high cycle fatigue life region. The effect of Ringerssolution as a lubricant is relatively greater in low cyclefatigue region, where the frictional force in Ringers solutionis about one third of that in air (Fig. 11), while effect ofRingers solution as corrosive agent is relatively greater inhigh cycle fatigue life region where fretting fatigue crackinitiates from pit formed on its surface (Fig. 12). For frettingfatigue of TNTZd12 in Ringers solution, the passive film onthe specimen surface is broken by fretting action, and as aresult, corrosion pits that lead to decrease fretting fatiguestrength in high cycle fatigue life region, are formed on itssurface.

3.5 Corrosion characteristics in 5%HCl and Ringerssolutions

Figure 13 shows the anodic polarization curves ofTNTZST, TNTZST aged at 673K for 259.2 ks, TNTZmultiand TNTZmulti aged at 673K for 259.2 ks obtained in 5%HClsolution with that of hot-swaged Ti-30Nb-10Ta-5Zr,18) whichhas 0.2%O and mirror surface produced by buff polishing,fabricated by powder metallurgy processing (hereafter Ti-30-10-5). The current density increases at the low potential

region, and the passive current density of TNTZST is a littlehigher than that of TNTZST aged at 673K for 259.2 ks,although the both critical current densities, Ic, are nearly thesame, that is around 0.7Am2. However, the corrosionresistance of TNTZST and TNTZST aged at 673K for 259.2 ksis lower than that of Ti-30-10-5. In general, the corrosionresistance of Ti is expected to be improved by alloying Nb, Zrand Ta.19) However, the behaviors of anodic polarizationcurves of TNTZST and TNTZST aged at 673K for 259.2 ksare pretty different from that of Ti-30-10-5. The criticalcurrent densities of TNTZST and TNTZST aged at 673K for259.2 ks are ten times greater than that of Ti-30-10-5. On theother hand, Ic and passive current densities at 0.6V, Ip, ofTNTZmulti and TNTZmulti aged at 673K for 259.2 ks are verysimilar to that of Ti-30-10-5. This trend was the same inRingers solution.

Figure 14 shows SEM micrographs and elemental map-ping images of TNTZST and TNTZmulti. The elementalmapping images using black and write colors shown in Figs.14(b) and (f) show the change in concentration of alloyingelement where the concentration of each element increaseswith increasing the dark image.

The stripe lines on surface of TNTZST parallel to therolling direction shown in Fig. 14(b) correspond to thechange in Ta content ratio (Fig. 14(c)). It is considered thatthe fluctuation of Ta concentration, which may be appearedduring the processing composed of melting and hot forging,is aligned with rolling direction. The difference between themaximum level and the minimum level of Ta concentrationwas found to be around 3mass% by EDX. The fluctuation ofNb or Zr concentration was not observed in this study. It wasdifficult to eliminate the stripe lines parallel to rollingdirection by solution treatment or aging conducted in thisstudy. The stripe lines on the surface of TNTZmulti parallel torolling direction related with the fluctuation of Ta concen-tration is eliminated completely (Figs. 14(f) and (g)).Therefore, each alloying element, in particular, Ta is dis-

Fri

ctio

nal F

orce

, F/ N

Maximum Cyclic Stress, max /MPa

0

100

200

300

400

500

0 100 200 300 400 500

Low Cycle Fatigue Life Region

Solid Symbol: in AirOpen Symbol: in Ringers Solution

Fig. 11 Relationships between frictional force, F, and maximum cyclic

stress, max, of TNTZd12 in air and Ringers solution.

20m

Pit

Crack Initiation Site

Fig. 12 SEM fractograph of TNTZd12 obtained from fretting fatigue tests

in Ringers solution in high cycle fatigue life region.

In 5% HCl Solution

Current Density, I / A. m-2

Pot

enti

al, E

/ V

vs.

SC

E

-1

-0.5

1

2

0.5

1.5

0

0.01 0.1 1 10

TNTZST

TNTZSTAged at 673 K

IC

TNTZmulti

TNTZmultiAged at 673 K

Ti-30Nb-10Ta-5Zr

Ip

Fig. 13 Anodic polarization curves of TNTZST, TNTZST aged at 673K for

259.2 ks TNTZmulti, TNTZmulti aged at 673K for 259.2 ks and hot swaged

Ti-30Nb-10Ta-5Zr in 5% HCl solution at 310K.


tributed homogeneously. As a result, it is considered that thecorrosion resistance of TNTZmulti is improved remarkably.

Figure 15 shows relationship between passive currentdensities, Ip, in 5%HCl and Ringers solutions of TNTZST,TNTZST aged at 673K for 259.2 ks, TNTZmulti and agedTNTZmulti at 673K for 259.2 ks with those of hot-rolled Ti-6Al-4V ELI conducted with aging,18) hot-rolled Ti-5Al-2.5Feconducted with aging18) and forged Ti-13Mo-5Zr-3Al con-ducted with annealing.18) Ip of TNTZmulti and TNTZmulti agedat 673K in 0.5%HCl and Ringers solutions are very lowvalues less than 0.1Am2 and have a correlation each other.While those of TNTZST and TNTZST aged at 673K aresignificantly scattered. They are much greater than that of Ti-5Al-2.5Fe, and are a little smaller than that of Ti-15Mo-5Zr-3Al or Ti-6Al-4V ELI.

4. Conclusions

Plain and fretting fatigue properties of newly developed type titanium alloy, Ti-29Nb-13Ta-4.6Zr, conducted withvarious heat treatments were investigated in this study. Thebasic corrosion characteristics of Ti-29Nb-13Ta-4.6Zr werealso investigated. The following results were obtained.(1) TNTZCR aged at 723K for 259.2 ks shows the greatest

fatigue strength in both low cycle fatigue and high cyclefatigue life regions, and the fatigue limit, which isaround 770MPa, is nearly equal to that of hot-rolled Ti-6Al-4V ELI conducted with aging.

(2) Fretting fatigue limits of the forged bar of Ti-29Nb-

13Ta-4.6Zr conducted with solution treatment(TNTZd12), and aging at 723K 172.8 ks after solutiontreatment are around 180MPa and 300MPa, respec-tively, which are much lower than those of plain fatiguelimits.

(3) For fretting fatigue of TNTZd12 in Ringers solution, thepassive film on the specimen surface is broken byfretting action, and as a result, corrosion pits that lead todecrease fretting fatigue strength in high cycle fatiguelife region, are formed on its surface.

(4) Passive current densities of the forged bars of Ti-29Nb-13Ta-4.6Zr conducted with multi-step-thermo-mechan-ical treatment (TNTZmult), where the cold rolling andsolution treatment are repeated 4 times, in 0.5%HCl andRingers solutions are much smaller than those of Ti-29Nb-13Ta-4.6Zr conducted with general heat treat-ments, and the values are a little smaller than those offorged Ti-15Mo-5Zr-3Al conducted with annealing andhot rolled Ti-6Al-4V ELI conducted with aging.

Acknowledgments

Some parts of this study are supported by NED (NewEnergy and Industrial Technology Development Organiza-tion, Tokyo, Japan), Grant-in-Aid for Promoting ScientificFrontier Research from Ministry Education, Science andCulture (Tokyo, Japan), Grant-in-Aid for Scientific Researchfrom Japan Society for Promotion of Science (Tokyo, Japan),Mitsubishi Foundation (Tokyo, Japan), Kotai Fundation(Tokyo, Japan), The Iron and Steel Institute of Japan (Tokyo,Japan), The Light Metal Education Foundation (Osaka,Japan), Suzuki Foundation (Hamamatsu, Japan) and theGrant for the Excellent Research Project of Research Centerfor Future Technology, Toyohashi University of Technology.T A would like to express great thanks to Professor DanielEylon, The University of Dayton (Ohio, USA) for hisassistance to complete this paper.

(f) EMI

(g) EMI of Ta

(b) EMI

(c) EMI of Ta

(a) SEM Micrograph

A

A

5 m

Rolling Direction

TNTZST

(d) SEM Micrograph

A

A

5m

Rolling Direction

TNTZmulti

Fig. 14 SEM micrographs and elemential mapping images (EMI) of

TNTZST and TNTZmulti.

0.01

0.1

1

10

0.01 0.1 1 10

Ti-30Nb-10Ta-5Zr

Ti-6Al-4V ELI

Ti-15Mo-5Zr-3Al

Ti-5Al-2.5Fe

Ip in 5%HCl Solution, / A. m-2

I p in

Rin

ger

s So

luti

on, /

A. m

-2 TNTZST

TNTZSTaged 673 K

TNTZmulti

TNTZmultiAged at 673 K

Fig. 15 Comparison of passive current density, Ip, of each titanium alloy in

5% HCl and Ringers solution.


REFERENCES

1) M. Niinomi: Mat. Mater. Trans. A 33A (2002) 477486.

2) Y. Okazaki, K. Kyo, Y. Ito, E. Nishimura and T. Tateishi: Materia

Japan 36 (1997) 10921099.

3) H. Hamanaka and T. Tsuchiya: Feramu Japan 2 (1997) 3035.

4) M. Niinomi, T. Hattori, K. Morikawa, T. Kasuga, A. Suzuki, H. Fukui

and S. Niwa, Mater. Trans. 43 (2002) 29702977.

5) D. Kuroda, M. Niinomi, H. Fukui, M. Morinaga, H. Suzuki and J.

Hasegawa: Tetsu-to-Hagane 86 (2000) 3239.

6) D. Kuroda, M. Niinomi, H. Fukui, H. Suzuki and J. Hasegawa: Tetsu-

to-Hagane 86 (2000) 4046.

7) R. Schenk: Titanium in Medicine, Springer, ed. by D. M. Brunette, P.

Tengvall, M. Textor and P. Thomesen, (2001) 144170.

8) B. Gasser: Titanium in Medicine, Springer, ed. by D. M. Brunette, P.

Tengvall, M. Textor and P. Thomesen, (2001) 673701.

9) Y. Okazaki: Materia Japan 37 (1998) 838842.

10) Y. Okazalo, K. Kyo, Y. Ito and T. Tateishi: Mater. Trans. 38 (1997)

163170.

11) T. Akahori, M. Niinomi K. Fukunaga and I. Inagaki: Metall. Mater.

Trans. A 31A (2000) 19371948.

12) M. Niinomi, T. Akahori, S. Nakamura, H. Fukui and H. Suzuki: Tetsu-

to-Hagane 88 (2002) 567574.

13) M. Niinomi: Materia Japan 37 (1998) 843846.

14) J. A. Davidson, F. S. Gergette: State of the Art Materials for Orthopedic

Devices, Soc. Manufacturing Engineers EM87-122 (1987) 1.

15) S. K. Lee, K. Nakazawa, M. Sumita and N. Maruyama: Fretting

Fatigue Current Technology and Practices, ASTM ed. by D. W.

Hoeppner, V. Chandrasekaran and C. B. Elliott III, (2001) pp. 199212.

16) M. Sumita, N. Maruyama and K. Nakazawa: Fretting Fatigue, ESIS ed.

by R. B. Waterhouse and T. C. Lindley, (2001) pp. 351361.

17) N. Maruyama, M. Sumita and K. Nakazawa: Tetsu-to-Hagane 76

(1990) 262269.

18) K. Ishimizu, M. Niinomi, T. Akahori, H. Fukui and H. Suzuki:

Collected Abstracts of the 2002 Fall Meeting of the Japan Inst. of Light

Metals (2002) p. 365.

19) Y. Okazaki, A. Ito, T. Tateishi and Y. Ito: J. Japan Inst. Metals 57

(1993) 338346.


Fatigue, Fretting Fatigue and Corrosion Characteristics

Documents

Transcript of Fatigue, Fretting Fatigue and Corrosion Characteristics