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Materials Science and Engineering A263 (1999) 193 – 199

Corrosion wear fracture of new

type biomedical titanium alloys

Mitsuo Niinomi a, *, Daisuke Kuroda b , Kei-ichi Fukunaga a , Masahiko Morinaga c ,

Yoshihisa Kato d , Toshiaki Yashiro d , Akihiro Suzuki e

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

Toyohashi 441-8580, Japan

b Graduate Student of Toyohashi Uni 6 ersity of Technology , 1-1, Hibarigaoka , Tempaku - cho , Toyohashi 441-8580, Japan

c Department of Materials Science and Engineering , Nagoya Uni 6 ersity , Furo - cho , Chikusa - ku , Nagoya 464-0814, Japan

d Market De 6 elopment Department , Daido Steel Co . Ltd ., 10, Ryugu - cho , Minato - ku , Nagoya 455-0022, Japan

e R&D Laboratory , Daido Steel Co . Ltd ., 2-30, Daido - cho , Minami - ku , Nagoya 457-8545, Japan

Abstract

type titanium alloy such as Ti-6Al-4V ELI has been most widely used as an implant material for artiﬁcial

hip joint and dental implant because of its high strength and excellent corrosion resistance. Toxicity of alloying elements in

conventional biomedical titanium alloys like Al and V, and the high modulus of elasticity of these alloy as compared to that of

bone have been, however, pointed out [1,2]. New

type titanium alloys composed of non-toxic elements like Nb, Ta, Zr, Mo and

Sn with lower moduli of elasticity, greater strength and greater corrosion resistance were, therefore, designed in this study. The

friction wear properties of titanium alloys are, however, low as compared to those of other conventional metallic implant materials

such as stainless steels and Co – Cr alloy. Tensile tests and friction wear tests in Ringer’s solution were conducted in order to

investigate the mechanical properties of designed alloys. The friction wear characteristics of designed alloys and typical

conventional biomedical titanium alloys were evaluated using a pin-on-disk type friction wear testing system and measuring the

Keywords : Biomedical titanium alloys; Biocompatibility; Corrosion friction wear; Mechanical properties; Modulus of elasticity

1. Introduction

Steinemann [3,4]. Kawahara has also reported the cyto-

toxicity of pure metals [4,5]. From the point of view of

modulus elasticity,

The necessity to substitute the hard tissue instrumen-

tations like artiﬁcial hip joints for functionally disor-

dered hard tissues like bone and teeth is growing

whereas the population of over 65 years and bedridden

old persons is increasing.

type titanium alloys have a greater

advantage. Therefore,

type titanium alloys composed

of non-toxic elements showing lower modulus of elas-

ticity and greater strength should be developed. En-

hanced properties such as increased corrosion

resistance, and improved tissue response are possible in

such

type titanium alloys

such as Ti-6Al-4V ELI, Ti-6Al-7Nb and Ti-5Al-2.5Fe

have been used for orthopedic implant materials be-

cause of their excellent combination of biocompatibil-

ity, corrosion resistance and mechanical properties.

However, toxicity of alloying elements and high moduli

of elasticity of these alloys as compared to that of bone

have been pointed out.

The cytotoxicity of pure metals, and the relationship

between biocompatibility and polarization resistance of

surgical implant materials have been reported by

type titanium alloys as compared to

type

alloys.

In this study, new type titanium alloys composed of

non-toxic elements such as Nb, Ta, Zr, Mo and Sn with

lower modulus of elasticity, greater strength and greater

corrosion resistance were designed using d-electron the-

ory [6].

The proper human joints have low friction and near

zero wear due to assured lubrication by various hydro-

dynamic and elastohydrodynamic mechanisms. Friction

wear of implant materials is a signiﬁcant clinical prob-

* Corresponding author.

PII: S0921-5093(98)01167-8

Metallic materials such as stainless steel, Co – Cr alloy, pure titanium and titanium alloys have been used for surgical implant

materials. The

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M . Niinomi et al . : Materials Science and Engineering A 263 (1999) 193–199

Table 1

type titanium alloys for implant material

1. Ti-13Nb-13Zr: near

type 5.13.Ti-15Mo-3Zr-3Al:

type

(USA), low modulus (ASTM)

(Japan), low modulus

2. Ti-12Mo-6Zr-2Fe:

type

6. Ti-15Mo-3Nb:

type (USA),

(USA), low modulus

low modulus

3. Ti-15Mo:

type (USA),

7. Ti-35.3Nb-5.1Ta-4.6Zr:

low modulus

type (USA), low modulus

4. Ti-16Nb-10Hf:

type

8. Ti-29Nb-13Ta-4.6Zr:

type

(USA), low modulus

(Japan), low modulus

a Alloys originally developed as implant materials.

lem. The loosen orthopedic implants cause pain and

restricted action. The surface treatments like ion nitrid-

ing and oxygen diffusion hardening are, therefore, tried

to increase the friction wear resistance, recently [7,8].

The friction wear resistance of titanium and titanium

alloys are, however, lower as compared to that of

conventional biomedical alloys such as Co – Cr alloys.

The friction wear characteristics of designed alloys

and typical conventional biomedical titanium alloys

were also evaluated in Ringer’s solution using a pin-on-

disk type friction wear testing system in this study. The

wear characteristics of designed alloys were evaluated

by the weight loss and width of groove of the specimen.

Tensile tests on designed

Fig. 1. (a) Schematic drawing of thermomechanical processing in

designed alloys and (b) Typical light micrographs of as-solutionized

designed alloys. S.T.: solution treatment, C.W.: cold working.

type biomedical titanium

alloys were also carried out for comparing those of

typical conventional biomedical titanium alloys.

type titanium alloys with high bio-

compatibility. However, it is very difﬁcult to evaluate

the all kind of toxicity of alloying elements. From the

conclusions of Steinemann and Kawahara [3,5], Nb,

Ta, Mo, Zr and Sn has been selected as alloying

elements. Employing a molecular orbital method, elec-

tron structure was calculated for bcc titanium alloyed

with a variety of elements, and two alloying parameters

were determined theoretically. The one is the bond

order (hereafter refereed to as B o ) which is a measure of

the covalent bond strength between titanium and alloy-

ing element. The other is the metal d-orbital energy

level ( M d ) which correlates with the electronegativity

and the metallic radius of elements. For alloys, the

average values of B

2. Experimental procedures

2.1. Design of new

type titanium alloys for implant

materials

type titanium alloys developed or

in the process of development are reported in Table 1.

The open circle indicates the alloy which has originally

developed as an implant material. The alloys are

roughly grouped as the high Nb content alloys or the

high Mo content alloys. Ti-13Nb-13Zr alloy which

composed of non-toxic elements like Nb and Ta is the

most expected one in the USA because of its excellent

The biomedical

( d are deﬁned by taking the

compositional average of B

( o and M

( d , and denote B

( o

( d , respectively [6]. The chemical compositions of

the designed alloys were listed with B

( o and M

( d values in

Table 2, respectively.

Table 2

Chemical compositions and values of B o and M d in designed alloys

2.2. Alloy processing

Alloy no.

Chemical compositions (mass%)

B o

M d

The appropriate mixtures of sponge titanium and

alloying elements were melted in button shaped ingot

(45 g) of designed alloys using a tri-arc furnace. The

ingots were heated at 1273 K for 21.6 ks for homoge-

nizing after melting, and then cold rolled by a reduction

of 75%. The cold rolled ingots were solutionized at

1117 K for 1.8 ks followed by aging at 673, 723 and 773

K for 14.4 ks. Heating and cooling were carried out in

Ti-29Nb-13Ta-4.6Zr

2.878

2.462

Ti-16Nb-13Ta4Mo

2.843

2.436

Ti-29Nb-13Ta

2.866

2.446

Ti-29Nb-13Ta-4Mo

Ti-29Nb-13Ta-2Sn

2.815

2.413

2.859

2.856

2.443

Ti-29Nb-13Ta-4.6Sn

Ti-29Nb-13Ta-6Sn

2.438

2.853

2.434

combinations of biocompatibility and mechanical

properties.

It is very important that the non-toxic elements must

be selected as alloying elements for developing of

biomedical new

and M

M . Niinomi et al . : Materials Science and Engineering A 263 (1999) 193–199

195

Fig. 2. Comparison of mechanical properties in each alloy. ST and STA indicate as-solutionized and aged conditions, respectively.

the argon atmosphere. The schematic drawing of the

thermomechanical processing for designed alloys and

as-solutionized (S.T) microstructures of the representa-

tive processed designed alloys are shown in Fig. 1.

2.3. Specimen preparation and tensile tests

Several 56 12 1.5 mm 3 tensile test specimens were

machined from a button ingot of the designed alloy.

The tensile tests were carried out using an Instron type

machine at a cross head speed of 8.33 10 6 ms 1 in

order to determine ultimate tensile strength, 0.2% proof

stress and elongation to fracture at room temperature.

The measurement of modulus of elasticity was done

using a piezoelectric composite-bar method at room

temperature.

Table 3

Young’s moduli of designed alloys and conventional biomedical

titanium alloys a

Chemical composition (mass%)

Young’s modulus (GPa)

S.T.

STA

2.4. Friction wear tests

Ti-6Al-4V ELI

Ti-13Nb-13Zr

112

64–77

The friction wear characteristics of designed alloys

and typical conventional biomedical titanium alloys

versus zirconia and alumina balls were evaluated using

a pin-on-disk type friction wear testing system in

Ringer’s solution. Specimens were in the geometry of

15 15 3mm 3 plate. Each wear test specimen was

ﬁnished using a 1500

Ti-29Nb-13Ta-4.6Zr b

Ti-16Nb-13Ta4-Mo b

Ti-29Nb-13Ta b

113

103

Ti-29Nb-13Ta-4Mo b

Ti-29Nb-13Ta-2Sn b

Ti-29Nb-13Ta-4.6Sn b

Ti-29Nb-13Ta-6Sn

emery paper before testing.

The friction wear tests were done against zirconia and

alumina balls, respectively with a load of 200 g at 310

a ST: as-solutionized; STA: aged after solutionized.

b Designed alloys.

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M . Niinomi et al . : Materials Science and Engineering A 263 (1999) 193–199

Fig. 3. Weight loss and width of groove of designed alloys and conventional alloys against a zircon ball.

Fig. 4. Weight loss and width of groove of designed alloys and conventional alloys against an alumina ball.

K in Ringer’s solution at room temperature. The tests

were done up to 5.0 10 4 cycles at 60 cycle min 1 . The

sliding speed for each test was 31.4 mm s 1 . The wear

characteristics were evaluated by measuring the weight

loss and width of groove of the specimen.

10.8 ks is the greatest among the other designed alloys

in this study. This designed alloy was, however, more

brittle. The tensile strength of Ti-29Nb-13Ta-4Mo

whose Nb content is increased is lower as compared to

that of Ti-16Nb-13Ta-4Mo. It is known in general that

type alloys with lower% Mo equivalent have a trend

to precipitate

phase at lower temperature. It is also

known that the tensile strength increases with

3. Results and discussion

phase

precipitate while the elongation decreases. The low

temperature at a temperature between 673 and 773 K

was carried out on the designed alloys in this study.

The precipitation of

3.1. Tensile properties

The mechanical properties of designed alloys were

shown in Fig. 2. Each as-solutionized (ST) designed

alloy has lower strength and equivalent or higher elon-

gation as compared to those of conventional medical

titanium alloys such as Ti-6Al-4V ELI and Ti-13Nb-

13Zr.

The tensile strength of Ti-29Nb-13Ta-4.6Zr con-

ducted with aging (STA) at 673K for 10.8 ks was

equivalent or greater as compared to those of conven-

tional medical titanium alloys. The tensile strength of

Ti-16Nb-13Ta-4Mo conducted with aging at 673 K for

phase will be the main cause for

increasing tensile strength and decreasing elongation in

Ti-16Nb-13Ta-4Mo.

3.2. Modulus of elasticity

The moduli of elasticity of designed alloys were listed

in Table 3. The moduli of elasticity of as-solutionized

designed alloys are equivalent or lower compared with

those of conventional biomedical titanium alloys as

listed in Table 3. In the aged condition where the aging

M . Niinomi et al . : Materials Science and Engineering A 263 (1999) 193–199

197

Fig. 5. Weight loss of plate of designed alloy with different heat treatment conditions and conventional biomedical titanium alloy, and alumina

and zircon balls. ST and STA indicate as-solutionized conditions and aged conditions, respectively.

Fig. 6. Light micrographs of wear surfaces of designed alloys, Ti-29Nb-13Ta-4.6Zr and Ti-29Nb-13Ta-4.6Sn, and a conventional biomedical

titanium alloy, Ti-6Al-4V ELI, against a zircon ball after wear tests.

Fig. 7. Light micrographs of wear surfaces of designed alloys, Ti-29Nb-13Ta-4.6Zr and Ti-29Nb-13Ta-4.6Sn, and a conventional biomedical

titanium alloy, Ti-6Al-4V ELI, against an alumina ball after wear tests.

temperature and time are 673 K and 10.8 ks, respec-

tively, Ti-29Nb-13Ta-4.6Zr shows equivalent or lower

modulus of elasticity compared with those of conven-

tional biomedical titanium alloys. Other designed alloys

in aged conditions also show equivalent or lower mod-

uli of elasticity compared with those of conventional

biomedical titanium alloys.

corrosion wear of designed alloys in Ringer’s solution is

completely opposite depending on the mating materials.

The designed alloys show smaller weight loss and width

of groove against a zircon ball compared with those of

conventional biomedical titanium alloys such as Ti-6Al-

4V and Ti-6Al-7Nb as shown in Fig. 3. On the other

hand, the weight loss and width of groove of designed

alloys against an alumina ball in Ringer’s solution are,

however, deﬁned to be greater compared with those of

conventional biomedical titanium alloys as shown in

Fig. 4. The trend in corrosion wear of designed alloys

in Ringer’s solution is completely opposite depending

on the mating materials, that is, pin materials.

The comparison of weight loss of specimens (plate)

and mating materials (ball) obtained from the corrosion

3.3. Friction wear characteristics

The weight loss and width of groove in designed

alloys and typical conventional biomedical titanium

alloys such as Ti-6Al-4V ELI and Ti-6Al-7Nb in STA

conditions against a zircon and alumina balls are

shown in Figs. 3 and 4, respectively. The trend in

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