Investigation on Mechanical Compatibility Matching for Biomedical Titanium Alloys

Transcription

1 Key Engineering Materials Vls (2005) pp Online available since 2005/Jun/15 at (2005) Trans Tech Publicatins, Switzerland di: / Zhenta Yu 1, a Investigatin n Mechanical Cmpatibility Matching fr Bimedical Titanium Allys Lian Zhu 2, b, Lijuan Lu 3, c Mahng Fan 4, d and Yanyan Fu 5, e 1, 2, 3, 5 Nrthwest Institute fr Nnferrus Metal Research, Xi an, Shaanxi (710016), China 4 Center fr Sustainable Envirnmental Technlgies, Iwa State University, Ames, IA 50011,The, U.S a yzt@c-nin.cm, b Zhul@c-nin.cm, d fan@ameslab.gv Keywrd: Titanium, near-β type titanium allys, mechanical prperties; matching f mechanical cmpatibility, surgical implants Abstract. The effects f allying elements such as M, Sn, Zr, Nb, defrming-rate, slid slutin and aging treatment n mechanical prperty and micrstructure f near βtype bimedical Ti allys based n Ti-Nb-Zr system were studied. The Influential factrs and their slutin were discussed t keep matching f strength, elastic mdulus, plasticity and tughness. Ti-Zr-M-Nb and Ti-Zr-Sn-M-Nb ally systems pssess excellent bicmpatibility, lwer elastic mdulus, higher strength, finer plasticity and fracture tughness matching by means f slid slutin and ageing treatment which are much mre suitable fr surgical implant and rthpedic materials. 1 Intrductin Ti and Ti allys are becming mre prmising bimedical materials cmpared with ther metal materials. But bimaterials (especially fr surgical implanting materials) require nt nly better bicmpatibility, but als finer mechanical cmpatibility t avid the implants failure caused by stress shielding [1]. Simultaneusly, enugh strength and tughness are needed t ensure the validity and reliability f implants. The metastable β type Ti allys such as Ti-13Nb-13Zr has been the mst attractive implanting material candidate recently [2]. It pssess lwer mdulus, imprved crrsin and wear resistance, high strength and tughness matching by means f selecting adequate allying elements, cntrl f melting, prcess and heat treatment system. The effects f allying elements such as M, Sn, Zr, Nb and wrking-rates, slid slutin and aging treatment n the mechanical prperties and micrstructure f nearβtype bimedical Ti allys based n Ti-Nb-Zr system were investigated.. 2 Experimental prcedures 7 kinds f nearβti ally were designed which M equivalences (M eq ) ranged frm 3.6~10.2 and numbered 3#~9# separately. 0 grade Ti spnge, pure Zr bar (4 2mm, 99.7wt%), pure Sn bar (5 2mm, 99.9wt%), pure M pwder and Nb 53 Ti 47 intermediate ally were used as raw materials. The ally ingts f 5Kg were melted by nn-cnsumable arc melting tw times t ensure chemical hmgeneity and lwer impurity cntents: Fe 0.10wt%, Si<0.04wt%, C 0.03wt%, N 0.02wt%, H 0.003wt%, O 0.10wt%. The ingts were frged abveβ-transus zne, then ht rlled int the rds f 12mm in diameter by tw kinds f defrming-rate fr testing f tensile mechanical prperties, and als mm ht frged bars fr fracture tughness. The specimens cut frm the rds and bars were subjected t a variety f heat treatment. The samples fr ptical metallgraphy, scanning electrn micrscpy (SEM) were prepared using standard techniques and etch with Krll s reagent (5ml HF, 10mlHNO 3 and H 2 O). 3. Results and discussin 3.1 Effect f allying elements The mechanical prperties f rlled rds f allys are shwn in table1. It is fund that the mduli f elasticity (E) f allys f 3#~9# lwer greatly and clser t that f natural bne (1~30GPa) cmpared with cmmercially pure Ti (C.P-Ti) and Ti-6Al-4V (TC4), and new allys als shw higher tensile strength(σ b ), yield strength (σ s ) and better plasticity (δ 5 in elngatin) With the increasing f Nb cntents(see N 5#, 6#), the strength and the mdulus f allys lwered and the plasticity enhanced. With the increasing f M cntents (N. 5#, 7#), the strength rise and the mdulus and plasticity decrease. With the increasing f Zr cntents (N. 4# 6#), the strength and mdulus increase and plasticity change cntrarily. Substituting Sn fr Zr (N. 6# 8# 9#), with the increasing f Sn cntents, the strength and mdulus decrease and plasticity increase (N.8# 9#), but their change scpe is smaller. It is als fund that, apart frm lwer E values f ally 3#~9#, the values f admissible strain (σ s /E) f allys are better matching t human bne which was reprted All rights reserved. N part f cntents f this paper may be reprduced r transmitted in any frm r by any means withut the written permissin f TTP, (ID: , Pennsylvania State University, University Park, USA-03/02/15,16:21:48)

2 596 Advanced Bimaterials VI that the σ s /E values f human crtical bne, cld-rlled C.P-Ti and TC4 are 0.67%, 0.66% and 0.85% separately [3]. Table 1 Mechanical prperties f new designed allys N. Allys M eq σ b σs δ 5 E σs/e Legend (Wt%) [MPa] [MPa] [%] [GPa] [%] 1# Cmmercially Pure Ti Cld-wrked 2# Ti-6Al-4V Cld-wrked 3# Ti-13Zr-13Nb Ht-wrked 4# Ti-15Zr-25Nb-3M Ht-wrked 5# Ti-5Zr-15Nb-3M Ht-wrked 6# Ti-5Zr-25Nb-3M Ht-wrked 7# Ti-5Zr-15Nb-6M Ht-wrked 8# Ti-3Zr-2Sn-25Nb-3M Ht-wrked 9# Ti-1Zr-4Sn-25Nb-3M Ht-wrked 3.2 Effect f defrming rates The mechanical prperties f new nearβti allys experienced different defrmatin are given in Table 2. It is shwn that the mre defrming-rates ε (ε=(d 0 -D 1 )/D 0, D 0 and D 1 are the diameter f start and end f rlled rds respectively) are, the higher the allys strength is, and the lwer the elngatin and elastic mdulus are. Befre heat treatment, the result, which the mduli f elasticity decrease with defrming-rate increasing, might result frm the frming f prcess textures [4]. The main rlling texture f metals with clsed packing hexagnal crystal (HCP) is (0001)[10 10 ], whereas <1 100 > is the directin f smallest elastic mdulus, s it is prbable that the nearβti allys (cntaining much mre α phase f HCP) with strnger rlling texture frmed alng <1 100 > directin under large defrming-rate lead t lw elastic mdulus. The reasn, which the elastic mdulus increases after slid slutin and aging treatment, results frm transfrmatin f prcess texture t recrystallizatin texture. During this curse, <1100> prcess texture which has the smallest elastic mdulus is substituted fr <0001> recrystallizatin texture which pssess the largest elastic mdulus. Table2. Effect f defrming rates n mechanical prperties f new designed allys ε=66% ε=80% N. Allys σ b δ 5 E σ b δ 5 E (Wt%) /MPa /% /GPa /MPa /% /GPa 2# Ti-13Zr-13Nb # Ti-15Zr-25Nb # Ti-5Zr-15Nb-3M Effect f heat treatment and micrstructure The tensile mechanical prperties f Ti-13Nb-13Zr ally with different slid slutin (ST) and slid slutin and aging(sta) treatment abve and belw βtransus temperature(735 C) are shwn in Fig.1, 2. The ST specimen shws lwer strength, better plasticity and much lwer mduli f elasticity. After aging treatment, the strength and E values f Ti-13Nb-13Zr ally increase apparently, but the elngatins decrease (Fig.1). It is als fund that the ally with ht rlling and STA under lw temperature has gd matching f tensile strength and fracture tughness, whereas fracture tughness (K IC ) f Ti-13Nb-13Zr ally decrease with the increasing f tensile strength under ther heat treatments (Fig.2). The micrstructure f Ti-13Nb-13Zr ally with ht wrked, ST and STA treatment are shwn in Fig.3. It shws typical defrmed micrstructure with large quantities f crushed primary α phase (α P ) and β phase (Fig.3a). The ally mainly cntains acicular martensite α phase after β slutin treated (β-st) and water quenching (WQ), and isaxial metastable β phase (β MS ) after β slutin treated and air cling (AC)(Fig.3b). The β MS and α phase start t disslve during aging at 510 C and then large quantities f finer secndary α phase (α s ) with dt r needle shape are frmed in β matrix (Fig.3c). The ally cnsists β ms and α P after α+β slutin treated (α+β-st) and air cling, and then α s with dt shape frmed after aging (figure 3d). Thus the aging leads t dispersin strengthening and fine grain strengthening f near β allys. Ti-13Nb-13Zr shws typical dimpled fracture after slutin and aging heat treatment (Fig.4a, b). 2

3 Key Engineering Materials Vls Elastic mdulus(gpa) 750 C/1h, WQ 750 C/1h, AC 680 C/1h, AC ST R ST+A1 Heat treatment ST+A2 Elngatin (%) 24 ST+A3 Fig. 1 Effects f heat treatments n tensile mechanical prperties f Ti-13Nb-13Zr ally (R-as rlled, ST-slid slutin, A1-aging at 510C/6h, A2- aging at 560C /6h, A3- aging at 610C /6h) Tensile strength (MPa) R β -S T /W Q Fracture tughness (MPa m) Ò b K IC 840 β -S T /W Q + A 1 α + β -S T / A C α + β -S T /A C + A 1 H e a t tre a tm e n t Fig.2 Relatinship between tensile strength and fracture tughness f Ti-13Nb-13Zr ally Fig.3 Micrstructure f Ti-13Nb-13Zr ally (a) as-rlled (b)βst/wq and aged at (c) 510C (d) α+βstac and aged at 510C 3.4 Matching f mechanical cmpatibility The mechanical prperties f metal materials have clser dependence n their chemical cmpsitin, micrstructure (phase), prcess and heat treatment. Allying elements Zr, M, Sn, Nb were prved excellent additives with superir bicmpatibility [5]. Zr, Sn named as neutral elements f Ti has higher slubility in bth α Ti and β Ti. The allys cntaining Zr, Sn can enhance strength and imprve plasticity f allys, thus the fine prcessing prperties can be guaranteed. M, Ta, Nb, named as β phase stabilized elements which can cmpletely slid slubilized in β phase, lwers the β transus temperature. M, Ta, Nb can cause mre strengthening effects n Ti, and imprve the ht 3

4 598 Advanced Bimaterials VI wrking prperties. It is mre attractive that element Zr, Ta, Nb is helpful t lwer mduli f elasticity f Ti allys [6]. Therefre, the nvel β type Ti allys shuld preferentially chse the nn-txic, finer elements such as Zr, M, Nb, Sn etc. Thus the ally systems such as Ti-Zr-M-Nb and Ti-Zr-Sn-M-Nb shuld be excellent chices, which have been prved frm Tab.1. Fig.4 Mrphlgy f tensile fractures f Ti-13Nb-13Zr ally (a)α+βst/ac, (b)α+βst/ac+a 1 Bimedical Ti allys shuld meet better mechanical cmpatibility ther than bicmpatibility. Apart frm lwer E and σ s /E values, the ally simultaneusly shuld pssess enugh strength and tughness t ensure the safety and quality f implanting materials. S it is imprtant n cntrl f allying elements, micrstructure, prcess and heat treatment. But strength, mduli f elasticity, plasticity and tughness are a cmplex cntradictin [7]. Generally speaking, with the increasing f strength, the fracture tughness decreases accrdingly (see Fig.2), and the plasticity als decreases, whereas the mduli f elasticity increase (see Fig.1). S researchers smetimes have t lwer sme strength values t ensure higher plasticity, tughness and lwer E values. It is discvered that the nearβtitanium allys mainly cnsist f isaxial micrstructure (namely β ms phase after AC) and needle r lamellar micrstructure (martensite α phase after WQ) which exhibits lwer strength, mduli f elasticity, tughness and excellent plasticity. After slid slutin and aging treatment (STA), The β MS r α start t disslve and then transfrm t large quantities f finer secndary α phase (α s ) with dt r needle shape in β matrix, which result in dispersin strengthening and fine grain strengthening. Therefre, the mechanical prperties f materials can adjust by cntrlling the size and quantity f precipitated α s by means f adequate prcess and heat treatment t realize the best matching f mechanical cmpatibility. Fr example, Ti-13Nb-13Zr experienced slid slutin at lw temperature (680 C/1h, AC) and aging (510 C/6h) can achieve apprpriate matching f higher tensile strength, lw elastic mdulus and gd plasticity and fracture tughness t meet the requirement f different surgical implants. 4. Cnclusin (1) Adding f element Zr M Sn can strengthen Ti allys, whereas element M, Nb and larger defrming-rate are helpful t decrease elastic mdulus. The strength and mdulus f the ht-rlled allys decrease bviusly after slid slutin treatment, and then increase after aging treatment. (2) Element Zr, M, Nb, Sn are chsed t design near β Ti allys Ti-Zr-M-Nb and Ti-Zr-Sn-M-Nb which pssess excellent matching f bicmpatibility and mechanical cmpatibility by cntrlling prcess and heat treatment. Acknwledgement This wrk was supprted by 863 Chinese high-tech prject (2002AA326070). The authrs gratefully thank the generus financial supprt f it. References [1] Sumner D,Gatahte J: Clin Orthp Relat Res. Vl.274 (1992), p.202. [2] M.Geetha, A.K. Singh, etc: Vl.329 (2001), p.264 [3] Steinemann S.G,Mausli P A, Semlitsch etc.: Titanium 92 science and Technlgy (TMS, Warrendale, 1993). [4] Wang Xizhe, Xia Jinsheng, Zhang Zhu etc: Acta Metallurgica Sinica Vl.35(1999),p.167 [5] Yu Zhenta, Zhu Lian, Wang keguang: Rare Metals Letters Vl.23(1)(2004),p.5 [6] Y.Sng, D.S.Xu, R.Yang etc: Material Science and engineering, Vl.A260 (1999),p.269 [7] Frs F.H, Bmberger H, B: J.Metals, Vl.37 (7) (1985), p. 28 4

5 Advanced Bimaterials VI / Investigatin n Mechanical Cmpatibility Matching fr Bimedical Titanium Allys /