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Materials Science and Engineering A243 (1998) 231 – 236

Mechanical properties of biomedical titanium alloys

Mitsuo Niinomi *

Department of Production Systems Engineering , Toyohashi Uni 6 ersity of Technology , 1-1 Hibarigaoka , Tempaku - cho , Toyohashi 441, Japan

Abstract

Titanium alloys are expected to be much more widely used for implant materials in the medical and dental ﬁelds because of

their superior biocompatibility, corrosion resistance and speciﬁc strength compared with other metallic implant materials. Pure

titanium and Ti – 6Al – 4V, in particular, Ti – 6Al – 4V ELI have been, however, mainly used for implant materials among various

titanium alloys to date. V free alloys like Ti – 6Al – 7Nb and Ti – 5Al – 2.5Fe have been recently developed for biomedical use. More

recently V and Al free alloys have been developed. Titanium alloys composed of non-toxic elements like Nb, Ta, Zr and so on

with lower modulus have been started to be developed mainly in the USA. The

Keywords : Biomedical titanium alloys; Mechanical properties; Fracture characteristics; Fatigue characteristics

1. Introduction

Therefore, their fracture characteristics, including ten-

sile and fatigue characteristics should be clearly un-

derstood with respect to microstructures. The fracture

characteristics in the simulated body environment

should also be identiﬁed because the alloys are used

as biomedical materials. The effect of living body en-

vironment on the mechanical properties is also very

important to understand.

The mechanical properties such as tensile character-

istics, fracture toughness, fatigue characteristics and

so on of various biomedical titanium alloys developed

to date will be described in this paper in as much

detail as possible. The effects of simulated body envi-

ronment and living body environment on the mechan-

ical properties will be also described in the paper.

Pure titanium and titanium alloys are now the most

attractive metallic materials for biomedical applica-

tions. Ti – 6Al – 4V has been a main biomedical tita-

nium alloy for a long period. New types of alloys like

Ti – 6Al – 7Nb [1] and Ti – 5Al – 2.5Fe [2] have been,

however, recently developed because of the problem

of toxicity of elements in the Ti – 6Al – 4V alloy and

the development of the required performance of the

alloy. Biomedical titanium alloys with much greater

biocompatibility have been proposed and are cur-

rently under development [3]. They are mainly

type

alloys have greater biocompatibility because their

moduli are much less than those of

type alloys

like Ti – 6Al – 4V and so on. They are also able to gain

greater strength and toughness balance compared with

type alloys.

These titanium alloys are mainly used for substitut-

ing materials for hard tissues. Fracture of the alloys

is, therefore, one of the big problems for their reliable

use in the body. The fracture characteristics of the

alloys are affected by changes in microstructure.

2. Titanium alloys for implant and dental materials

Titanium alloys developed for implant materials to

date are listed in Table 1 [1 – 3,5 – 13]. Commercial

pure titanium, Ti – 6Al – 4V and Ti – 6Al – 4V ELI have

basically been developed for structural materials al-

though they are still widely used as representative tita-

nium alloys for implant materials. More recently, V

free

* Tel.: 81 532 446706; fax: 81 532 446690; e-mail:

r2mnlo@edu.tut.cc.tut.ac.jp

type alloys such as Ti – 6Al – 7Nb [1] and

Ti – 5Al – 2.5Fe [2] have appeared as implant materials.

PII S0921-5093(97)00806-X

type alloys are now the main target for medical

materials. The mechanical properties of the titanium alloys developed for implant materials to date are described in this paper.

alloys composed of non-toxic elements. The

232

M . Niinomi : Materials Science and Engineering A 243 (1998) 231–236

type alloys com-

posed of non-toxic elements like Ti – 15Sn – 4Nb – 2Ta –

0.2Pd and Ti – 15Zr – 4Nb – 4Ta – 0.2Pd have been

developed [4]. Low modulus alloys are nowadays de-

sired because the moduli of alloys are required to be

much more similar to that of bone. The

The tensile properties of dental casting titanium al-

loys are listed in Table 2. The elongation of the alloys

are fairly lower than those of wrought or forged im-

plant alloys as shown in Table 3 and Fig. 1.

type alloys

have been, therefore, developed or are developing

mainly in the USA [3]. They are composed of non-

toxic elements like Nb, Ta, Zr and so on.

Pure titanium and Ti – 6Al – 4V type alloys are also

the main implant materials in the dental ﬁeld. The

titanium alloys for dental implant materials are, how-

ever, the same as those for surgical implant materials.

The alloys for other dental usage like crown, clasp

and so on have somewhat different compositions

compared with those for surgical implant materials

except for Ti – 6Al – 4V and Ti – 6Al – 7Nb as listed in

Table 2 [14]. They are in general processed by casting.

4. Modulus

The moduli of elasticity of biomedical titanium alloys

are shown in Fig. 2 although their values have been

already shown in Table 3 [3,5,6,10,11,13]. The moduli of

other metallic biomaterials like stainless steel and Co

type alloy are round 206 and 240 GPa, respectively [6].

They are much greater than that of bone whose modulus

of elasticity is generally between 17 and 28 GPa [6]. The

moduli of elasticity of biomedical titanium alloys are

much smaller than those of other metallic biomaterials.

The moduli of recently developed

type biomedical titanium alloys. They are

however greater than that of bone.

and

3. Tensile properties

The tensile properties of titanium implant materials

developed to date are listed in Table 3 [1 – 13]. The

data of tensile yield stress and elongation in Table 3

are plotted in Fig. 1 with those of structural

5. Fatigue strength

Fatigue strength of biomedical titanium alloy at 10 7

cycles are shown in Fig. 3 [8,10,13] with those of

other metallic biomedical materials such as stainless

steels; AISI 316 LVM and SUS 316L and Co type

alloys; Co – Cr – Mo and Co – Ni – Cr – Mo. Fatigue

strength of biomedical titanium alloys listed in Table

3 is from 265 to 816 MPa.

type titanium alloys. The data of the structural

titanium alloys are shown as a scatter band in Fig. 1.

The yield strength of biomedical titanium alloys are

distributed nearly between 500 and 1000 MPa. The

yield strength of pure titanium designated by

type

biomedical titanium alloys is slightly lower than that

of the structural one. The elongation of biomedical

titanium alloys is distributed between

10 and 20%.

6. Fracture toughness

Table 1

Titanium alloys for biomedical applications

Fracture toughness of biomedical titanium alloys

are shown in Fig. 4 [4,6,13]. The fracture toughness of

type medical titanium alloys are similar to those of

1. Pure titanium (ASTM F67):

type (USA), low modulus a

9. Ti – 13Nb – 13Zr: near

type ones.

Grade 1, 2, 3 and 4

2. Ti – 6Al – 4V ELI (Wrought:

10. Ti – 12Mo – 6Zr – 2Fe:

type

ASTM F136 and forged:

ASTM F620):

(USA), low modulus a

7. Fatigue behavior in simulated body environment

type

3. Ti – 6Al – 4V (Casting: F1108): 11. Ti – 15Mo:

type (USA),

7.1. Fatigue strength

type

4. Ti – 6Al – 7Nb (ASTM F1295): 12. Ti – 16Nb – 10Hf:

low modulus a

type

type (Switzerland) a

5. Ti – 5Al – 2.5Fe (ISO:DIS

(USA), low modulus a

S – N curves of Ti – 6Al – 4V ELI with equiaxed and

Widmanst¨tten

13. Ti – 15Mo – 5Zr – 3Al:

type

structure and annealed SUS 316L in

air and Ringer’s solution obtained from rotating

bending fatigue tests have been reported [15]. The ro-

tating bending fatigue strength of Ti – 6Al – 4V ELI in

air and Ringer’s solution are equivalent. The fatigue

strength of SUS 316L is degraded in Ringer’s solution

at relatively greater number of cycles to failure com-

paring with that in air. The concentration of oxygen

in body liquid or muscle tissue except blood is rather

5832 – 10):

rich

type

(Japan), low modulus

(Germany) a

6. Ti – 5Al – 3Mo – 4Zr: a b type 14. Ti – 15Mo – 3Nb: b type

(Japan) a

(USA), low modulus a

7. Ti – 15Sn – 4Nb – 2Ta – 0.2Pd:

15. Ti – 35.3Nb – 5.1Ta – 7.1Zr: b

type (USA), low modulus a

a b type (Japan) a

8. Ti – 15Zr – 4Nb – 2Ta – 0.2Pd:

16. Ti – 29Nb – 13Ta – 4.6Zr: b

a b type (Japan) a

type (Japan), low modulus a

a Developed for biomedical applications.

In addition, V and Al free

type alloys are

between 55 to 85 GPa. They are much smaller than that

and

M . Niinomi : Materials Science and Engineering A 243 (1998) 231–236

233

Table 2

Titanium alloys for dental applications and their mechanical properties

Alloy

Process

Tensile strength

Yield strength

Elongation

Vickers hardness

(Mpa)

(%)

(Hv)

1. Ti – 20Cr – 0.2Si

Casting

874

669

318

2. Ti – 25Pd – 5Cr

Casting

880

659

261

3. Ti – 13Cu – 4.5Ni

Casting

703

—

2.1

—

4. Ti – 6Al – 4V

Casting

976

847

5.1

—

5. Ti – 6Al – 4V

Superplastic forming

954

729

346

6. Ti – 6Al – 7Nb

Casting

933

817

7.1

7. Ti – Ni

Casting

470

—

190

Table 3

Mechanical properties of titanium alloys for biomedical applications

Alloy

Tensile strength

Yield strength

Elongation (%)

RA (%) Modulus (GPa)

Type of alloy

(UTS) (Mpa)

( s y )

1. Pure Ti grade 1

240

170

102.7

2. Pure Ti grade2

345

275

102.7

3. Pure Ti grade 3

450

380

103.4

4. Pure Ti grade 4

550

485

104.1

5. Ti – 6Al – 4V ELI (mill An-

860 – 965

795 – 875

10 – 15

25 – 47

101 – 110

nealed)

6. Ti – 6Al – 4V (annealed)

895 – 930

825 – 869

6 – 10

20 – 25

25 – 45

110 – 114

7. Ti – 6Al – 7Nb

900 – 1050

880 – 950

8.1 – 15

114

8. Ti – 5Al – 2.5Fe

1020

895

112

9. Ti – 5Al – 1.5B

925 – 1080

820 – 930

15 – 17.0

36 – 45

110

10. Ti – 15Sn – 4Nb – 2Ta – 0.2Pd

(Annealed)

860

790

(Aged)

1109

1020

103

11. Ti – 15Zr – 4Nb – 4Ta – 0.2Pd

a b

(Annealed)

715

693

(Aged)

919

806

12. Ti – 13Nb – 13Zr (aged)

973 – 1037

836 – 908

10 – 16

27–53

79–84

13. TMZF (Ti – 12Mo – 6Zr – 2Fe)

1060 – 1100

100 – 1060

18–22

64–73

74–85

(annealed)

14. Ti – 15Mo (annealed)

874

544

15. Tiadyne 1610 (aged)

851

736

16. Ti – 15Mo – 5Zr – 3Al

(ST)

852

838

(aged)

1060 – 1100

1000 – 1060

18 – 22

64 – 73

17. 21RX (annealed) (Ti –

979 – 999

945 – 987

16 – 18

15Mo – 2.8Nb – 0.2Si)

18. Ti – 35.3Nb – 5.1Ta – 7.1Zr

596.7

547.1

19.0

68.0

55.0

19. Ti – 29Nb – 13Ta – 4.6Zr

911

864

13.2

(aged)

small. The fatigue strength of Ti – 5Al – 2.5Fe in

Ringer’s solution with introducing N 2 gas, by which

the oxygen concentration in Ringer’s solution can be

lowered, has been studied. The results are shown in

Fig. 5 [15], with the data in the ordinary Ringer’s

solution. The fatigue strength of Ti – 5Al – 2.5Fe

beyond 10 6 cycles is smaller in the Ringer’s solution

with lower oxygen content than in the ordinary

Ringer’s solution. On the other hand, the fatigue

strength of Ti – 6Al – 4V has been reported not to

be degraded in living rabbit body [16] where oxygen

concentration can be considered to be rather small

compared with that in the air. These different trends

will come from the difference in the stress conditions

of fatigue testing methods. Ti – 5Al – 2.5Fe was fa-

tigued under rotating bending conditions while Ti –

6Al – 4V

was

fatigued

under

tension-tension

conditions.

234

M . Niinomi : Materials Science and Engineering A 243 (1998) 231–236

men in the Ringer’s solution is longer (a greater num-

ber of cycles).

7.2. Fatigue crack propagation beha

ior

The fatigue crack propagation rate of titanium al-

loys is apparently affected by simulated body environ-

ment [16,17]. The fatigue crack propagation rate of

pure titanium in 0.9% NaCl solution is greater than

that in dry air [16]. The same trend has been reported

for T – L direction of Ti – 6Al – 4V rolled plate in 3%

NaCl solution [17].

Fig. 1. Relationship between yield strength, s y , and elongation of

biomedical titanium alloys shown with the data of structural titanium

alloys.

8. Mechanical properties after implanted in living body

Titanium alloys have greater corrosion resistance

because the titanium oxide ﬁlm formed on the surface

of alloys acts as an electrochemically passive ﬁlm and

inhibits negative ions from invading the matrix of the

alloys. The fracture of the passive ﬁlm is highly possi-

ble when the bending stress is loaded on the speci-

men, even if the specimen itself is not fractured. The

fracture of the specimen by corrosion fatigue will be

accelerated in the Ringer’s solution with lower oxygen

content, where N 2 gas is introduced because the frac-

tured oxide ﬁlm will not reform sufﬁciently. The cor-

rosion fatigue will occur easily in such an

environment when the immersing time of the speci-

structure and SUS 316L

before and after implanting into the paravertebral

muscle of living rabbit for about 11 months are

shown in Fig. 6 [15]. The Vickers hardness of both

titanium alloys are not changed before and after im-

planting. The Vickers hardness of SUS 316L after

implanting is however increased compared with that

before implanting. The surface hardened area thick-

ness was found to be around 80

The fracture toughness of Ti – 5Al – 2.5Fe and Ti –

6Al – 4V ELI has been reported to be unchanged be-

fore and after implanting into living rabbits [15].

Fig. 2. Comparison of modulus of elasticity of biomedical titanium alloy.

The Vickers hardness changes on the specimen sur-

faces of implant materials Ti – 5Al – 2.5Fe and Ti –

6Al – 4V ELI with equiaxed

M . Niinomi : Materials Science and Engineering A 243 (1998) 231–236

235

Fig. 3. Fatigue strength at 10 7

cycles of biomedical titanium alloy. Data without designation of rotating bending are those obtained from uniaxial

fatigue tests.

Fig. 4. Fracture toughness of biomedical titanium alloy. K Q means invalid fracture toughness.

9. Summary

body environment with rather lower oxygen concentra-

tion. The crack propagation rate of biomedical tita-

nium alloys is grater in simulated body environments in

air.The Vickers hardness of the specimen surfaces and

fracture toughness of biomedical titanium alloys are

not changed before and after implanting into the living

rabbit while the Vickers hardness of the specimen sur-

face of SUS 316L after implanting is greater than that

before implanting.

The tensile strength of biomedical titanium alloys

developed to date lies between 500 and 1000 MPa. The

elongation lies between 10 and 20%. The moduli of

elasticity of the low modulus

type biomedical tita-

nium alloys developed to date is between 55 and 85

MPa.The rotating bending fatigue strength of the

biomedical titanium alloy is degraded in simulated

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