Effect of thermo-mechanical treatment on mechanical properties and shape memory behavior of Ti–(26–28) at.% Nb alloys

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  • Materials Science and Engineering A 438440 (2006) 839843

    Effect of thermo-mechanical treatment on6os

    sukuchno

    ary 20

    Abstract

    The effec emoin order to d cimeranges betw andsuperelastic perin the soluti critiAn aging tr relasttensile stren incredecreased w e aginphase. The aging effect increased with decreasing Nb content. In particular, perfect superelastic behavior was obtained with the strain up to 3% inthe Ti26 at.% Nb alloy annealed at 873 K followed by aging at 573 K for 3.6 ks. 2006 Elsevier B.V. All rights reserved.

    Keywords: Ti-base alloys; Biomedical shape memory alloys; Superelasticity; Thermo-mechanical treatment; TiNb

    1. Introdu

    TiNi smaterials ocorrosion rTiNi alloyproducts, tstrongly reNi. RecentlbiomedicalThe -type(disorderebic martenmemory efTiNb, Tithe reversio-type Ti a

    CorresponE-mail ad

    0921-5093/$doi:10.1016/jction

    hape memory alloys have been used as biomedicalwing to their excellent mechanical properties, highesistance and superior superelasticity. Although thes have been successfully applied for many medical

    he development of Ni-free shape memory alloys isquired because of Ni-hypersensitivity and toxicity ofy the -type Ti alloys have attracted attention as newshape memory and superelastic materials [112].Ti alloys exhibit a martensitic transformation fromd BCC) to hexagonal martensite () or orthorhom-

    site() depending on alloy composition. The shapefect and superelastic behavior have been reported inMo and TiV based alloys. It has been confirmed thatn of to results in shape memory behavior in thelloys. The present authors have paid attention to Mo

    ding author. Tel.: +81 29 853 5283; fax: +81 29 853 5283.dress: miyazaki@ims.tsukuba.ac.jp (S. Miyazaki).

    and Nb as a -stabilizer [614] because of cytotoxicity of V.We have reported that the Ti(2227) at.% Nb alloys exhibitedshape memory effect and superelastic behavior at room temper-ature [11]. But, the low critical stress for slip deformation causedthe superelasticity not to reveal a large strain in binary TiNballoys.

    In this study, effect of thermo-mechanical treatmenton mechanical properties and shape memory behavior ofTi(2628) at.% Nb alloys was investigated in order to developbiomedical shape memory alloys. The shape memory propertyand microstructure were investigated by cyclic tensile tests anda transmission electron microscope.

    2. Experimental procedure

    The Ti(2628) at.% Nb alloys were prepared by the Ar arcmelting method. The ingots were homogenized at 1273 K for7.2 ks and cold-rolled with the reduction of 95 or 99% in thick-ness. Specimens for the mechanical tests were cut from the cold-rolled sheet by an electro-discharge machine. The specimenswere cleaned with ethanol, wrapped in Ti foils and encapsulated

    see front matter 2006 Elsevier B.V. All rights reserved..msea.2006.02.136shape memory behavior of Ti(2H.Y. Kim a, J.I. Kim a, T. Inamura b, H. H

    a Institute of Materials Science, University of Tsukuba, Tb Precision and Intelligence Laboratory, Tokyo Institute of Te

    Received 13 June 2005; received in revised form 10 Janu

    t of thermo-mechanical treatment on mechanical properties and shape mevelop biomedical shape memory alloys. For the solution treated speeen 293 and 313 K in Ti26 at.% Nb, 193 and 313 K in Ti27 at.% Nbbehavior with a strain larger than 2% could not be obtained at room temon treated alloys. Low temperature annealing (at 873 K) increased theeatment at 573 K after annealing at 873 K further improved the supegth and the critical stress for inducing the martensitic transformationith increasing aging time. The increase of the tensile strength and thmechanical properties and28) at.% Nb alloysoda b, S. Miyazaki a,ba, Ibaraki 305-8573, Japanlogy, Yokohama 226-8503, Japan06; accepted 6 February 2006

    ry behavior of Ti(2628) at.% Nb alloys was investigatedns, superelastic behavior was observed in the temperature163 and 233 K in Ti28 at.% Nb alloys. However, perfectature because of the low critical stress for slip deformationcal stress for slip and stabilized the superelastic behavior.ic properties of the Ti(2628) at.% Nb alloys. Both theased with increasing aging time. However, the elongationg embrittlement were due to the formation of thermal

  • 840 H.Y. Kim et al. / Materials Science and Engineering A 438440 (2006) 839843

    in quartz tubes under a 3.3 kPa partial pressure of high-purity Ar,and then heat treated at 1173 K for 3.6 ks or at 873 K for 0.6 ks.Some specimens were aged at 573 K for various times. The spec-imens were quenched into water by breaking the quartz tubes.The oxidized surface was removed by mechanical polishing fol-lowed by electro-polishing. Tensile tests were carried out at astrain rate of 1.67 104 s1 at various temperatures. The gagelength of the specimens was 20 mm. Specimens for transmissionelectron microscopy (TEM) observation were also prepared bya conventional twin-jet polishing technique. TEM studies wereconducted using a JEOL2010F microscope operated at 200 kV.

    3. Results and discussion

    Fig. 1 shows a series of stressstrain curves obtained at var-ious temperatures for the Ti(2628) at.% Nb alloys after thesolution treatment at 1173 K for 3.6 ks. The specimens whichdo not exhibit complete superelastic recovery upon unloadingwere heated up to about 500 K: broken lines with an arrow indi-cate the shape recovery by heating. The shape memory effect wasobserved for the Ti26 at.% Nb alloy deformed at temperaturesbetween 193 and 273 K. Complete shape recovery occurred byheating to about 500 K. Superelastic behavior was observed at293 and 313 K although the shape recovery was incomplete. Thesuperelastiature. The ccritical streof 273333ature (Ms)Ti27 at.%observed astrain wastemperatur313 K in thited excelle

    Fig. 1. Stresstemperatures

    Fig. 2. EffectNb alloy.

    and 233 K.perature. Stemperaturthe martencritical streSlip occursthan the strdeformatiorecoverable

    critot tallo

    . 2 sre foraturs obof 57ieldi11stre

    re. Ting tecomand aer, i

    e. theinge strromfor the Ti26 at.% Nb alloy are mainly due to the change

    microstructure such as dislocation density and grain size.odal grain structure consisting of fine subgrains and largetallized grains was observed in the specimen heat treatedK for 3.6 ks. On the other hand, a fully recrystallizedtructure was observed in the specimens heat treated atd 1173 K. The decrease in the yield stress with increas-at treatment temperature from 973 and 1173 K is due torease in grain size. This indicates that the low tempera-nealing is effective for increasing the critical stress for

    nent deformation. Also it has been reported that aging atis effective to increase the critical stress for the solutionTi(2527) at.% Nb alloys [11].c strain decreased with further increasing test temper-ritical stress for apparent yielding corresponds to thess to induce the martensite in the temperature rangeK since the martensitic transformation start temper-of the Ti26 at.% Nb is about 273 K [11]. For theNb alloy, incomplete superelastic behavior was also

    t temperatures between 193 and 313 K. The residualrecovered by heating. This indicates that the finishe of the reverse transformation (Af) is higher thane Ti27 at.% Nb alloy. The Ti28 at.% Nb alloy exhib-nt superelastic behavior at temperatures between 163

    strain curves obtained upon loading and unloading at variousfor the Ti(2628) at.% Nb alloys.

    the lowticity nTiNb

    Figperatutempeure wa

    rangeafter yof 873tensileperatuannealalloy b873 KHowevtion, i.annealfracturature fcurves

    in theA bimrecrysat 873grain s973 aning hethe incture anperma573 Ktreatedof annealing temperature on stressstrain curve of the Ti26 at.%

    The residual strain increased with increasing tem-hape recovery was hardly observed when the teste was higher than 273 K. The critical stress to inducesite increased with increasing temperature, while thess for slip decreased with increasing temperature.if the critical stress level for slip becomes lower

    ess to induce the martensite. Thus, the strain by slipn increased with increasing temperature, causing the

    strain to decrease. As a result, it is concluded thatical stress for slip deformation caused the superelas-o reveal a large strain in the solution treated binaryys.hows the stressstrain curves obtained at room tem-r the Ti26 at.% Nb alloy after annealing in the

    e range of 5731173 K for 3.6 ks. Premature fail-served in the specimens annealed in the temperature3673 K. The specimen annealed at 773 K fracturedng. The specimens annealed in the temperature range73 K exhibited a two-stage yielding. The ultimatength (UTS) decreased with increasing annealing tem-he fracture strain steeply increased with increasingemperature from 773 to 1173 K. The Ti26 at.% Nb

    es single phase when the alloy is heat treated atbove, since the transus temperature is about 823 K.t is noted that the yield stress for plastic deforma-second stage yield stress, decreased with increasing

    temperature from 873 to 1173 K. Furthermore, theain increased with increasing heat treatment temper-873 to 973 K. The differences in the stressstrain

  • H.Y. Kim et al. / Materials Science and Engineering A 438440 (2006) 839843 841

    Fig. 3. Stress 26 atat 573 K for (

    In orderincrement cNb specimresult is shothe specimAt the firstabout 1.5%The similaimum straiThe perfecspecimen aby heatingsile strain,remained p

    The spefect supereplastic strathe superelaged for 3.6lasticity wsuperelastiis obviouscorrespondmation, incmens. Thewith incresuperelastireached 66imen agedwell knownposition ofthat the pretent of ma

    ionnicae traeaso

    rmase. Ies we isatio

    . 4(aondstrain curves obtained by cyclic loadingunloading tensile tests for (a) the Tib) 1.8 ks, (c) 3.6 ks and (d) 36 ks after annealing.

    to investigate the shape memory behavior, strainyclic tensile tests were carried out for the Ti26 at.%

    en subjected to annealing at 873 K for 0.6 ks, and thewn in Fig. 3. Fig. 3 also shows stressstrain curves of

    ens aged at 573 K after annealing at 873 K for 0.6 ks.cycle, tensile stress was applied until strain reached, and then the stress was removed in the specimen.

    r measurement was repeated by increasing the max-n by 0.5% upon loading using the same specimen.t superelasticity was obtained at the first cycle in thennealed at 873 K. Complete shape recovery occurred

    formatmechaing thit is rtransfo phaincreas phasdeform

    Figcorrespat the second and third cycles. As increasing ten-the superelastic behavior became incomplete and thelastic strain increased.cimen aged at 573 K for 1.8 ks exhibited almost per-lasticity at the first and second cycles. The remainedin increased with increasing applied strain althoughastically recovered strain increased. The specimenks revealed excellent superelasticity. Perfect supere-

    as observed until the fourth cycle. The maximumc strain of 3.3% was obtained at the fifth cycle. Itthat the critical stress for the first yielding, whichs to the stress for inducing the martensitic transfor-reased when compared with the other two speci-

    maximum stress reached at each cycle also increasedasing aging time. It is also noted that the stablecity was observed even though the maximum stress0 MPa upon loading. On the other hand, the spec-for 36 ks fractured at the third cycle. It has beenthat the phase is Ti-rich although the exact com- phase is difficult to be determined. This impliescipitation of thermal phase increases the Nb con-trix, resulting in decrease of the martensitic trans-

    aged at 87was obtainmary reflecpositions cthe selecteda dimensiomicrograph phase wThe selectegraphs obtFig. 4. Asbecame disparticles inticles large573 K for 3was quite btensile streaging at 57phase. It issevere lossand denseproperty of.% Nb alloy annealed at 873 K for 0.6 ks and the specimens aged

    temperature. Furthermore, the dispersed particleslly suppress the martensitic transformation, also caus-nsformation temperature to decrease. As a result,nable that the stress for inducing the martensitiction increased by the precipitation of the thermalt is also noted that the second stage yield stressith increasing aging time, indicating that the thermal

    also effective for increasing the critical stress for slipn.) represents a dark field TEM micrograph and theing selected area diffraction pattern of the specimen

    3 K for 0.6 ks. The selected area diffraction patterned from the [1 1 0] zone axis. In addition to the pri-tions from matrix, diffuse scattering at 1/3 {1 1 2}orresponding to the athermal phase is visible in

    area diffraction pattern. Very fine particles withn of 3 nm were observed in the dark field TEM. These particles are considered as the athermal

    hich was formed during quenching after annealing.d area diffraction patterns and dark field TEM micro-ained from the aged specimens were also shown inincreasing aging time, the reflections from phasecrete spots and the size and volume fraction of creased as shown in the dark field images. The par-r than 20 nm were observed in the specimen aged at6 ks although the size distribution of the specimenroad. This indicates that the substantial increase of

    ngth and improvement of superelastic property after3 K for 3.6 ks are due to the growth of thermal also noted that aging at 573 K for 36 ks resulted in aof ductility. In conclusion, it is suggested that the fine

    precipitates are effective for improving superelasticthe binary TiNb alloys.

  • 842 H.Y. Kim et al. / Materials Science and Engineering A 438440 (2006) 839843

    Fig. 4. Dark-field TEM micrographs and the corresponding selected area diffraction patterns ofsubsequently aged at 573 K for (b) 1.8 ks, (c) 3.6 ks and (d) 36 ks.

    Fig. 5. Stressstrain curves obtained by cyclic loadingunloading tensile testsfor the Ti27 at.% Nb and Ti28 at.% Nb alloys annealed at 873 K for 0.6 ks andthe specimens subsequently aged at 573 K for 3.6 ks.

    SimilarNb and Tifor 0.6 ks astressstraifollowed bthat almostond cycleannealed atwith increadecreases wfor inducinstable supein both alloyield stressis reasonabNb contentsuperelastithermo-meare promis

    4. Conclu

    (i) The shobservThe s(a) the specimen annealed at 873 K for 0.6 ks and the specimens

    cyclic tensile tests were carried out for the Ti27 at.%28 at.% Nb alloys subjected to annealing at 873 Knd the result is shown in Fig. 5. Fig. 5 also showsn curves of specimens annealed at 873 K for 0.6 ksy aging treatment at 573 K for 3.6 ks. It can be seen

    perfect superelasticity was observed until the sec-in the Ti27 at.% Nb and Ti28 at.% Nb specimens873 K for 0.6 ks. The apparent yield stress increased

    sing Nb content. This is due to that theMs temperatureith increasing Nb content, causing the critical stress

    g the martensitic transformation to increase. Morerelasticity was obtained after aging at 573 K for 3.6 ksys. It is also noted that the increment of the apparentby aging decreased with increasing Nb content. Thisle because the stability of increases with increasing[15]. Based on the above results, it is concluded that

    c property of the TiNb alloys can be improved bychanical treatment and the Ti(2628) at.% Nb alloysing for the biomedical superelastic alloys.

    sions

    ape memory effect and/or superelastic behavior wereed in the solution treated Ti(2628) at.% Nb alloys.

    uperelastic behavior was observed in the tempera-

  • H.Y. Kim et al. / Materials Science and Engineering A 438440 (2006) 839843 843

    ture ranges between 293 and 313 K in the Ti26 at.% Nb,193 and 313 K in the Ti27 at.% Nb and 163 and 233 Kin the Ti28 at.% Nb alloys, respectively. However, perfectsuperelastic behavior with a strain larger than 2% could notbe obtained at room temperature because of the low criticalstress for slip deformation in the solution treated alloys.

    (ii) Ultimate tensile strength decreased and fracture strainincreased with increasing annealing temperature. The lowtemperature annealing at 873 K stabilized the superelastic-ity in the Ti(2628) at.% Nb alloys.

    (iii) The aging treatment at 573 K after annealing at 873 Kincreased both of the tensile strength and the critical stressfor inducing the martensitic transformation due to the for-mation of thermal phase in the Ti(2628) at.% Nballoys. However, the elongation decreased with increasingaging time. Perfect superelastic behavior was obtained withthe strain up to 3% by annealing at 873 K followed by sub-sequent aging at 573 K for 3.6 ks in the Ti26 at.% Nb alloy.

    Acknowledgments

    This work was partially supported by ILC Project from Uni-versity of Tsukuba and the 21 Century Center of Excellence Pro-gram and the Grants-in-Aid for Fundamental Scientific Research(Kiban A (19992001), Kiban A (20022004) from the Ministryof Education, Culture, Sports, Science and Technology, Japan.

    References

    [1] T.W. Duerig, J. Albrecht, D. Richter, P. Fischer, Acta Metall. 30 (1982)21612172.

    [2] W.F. Ho, C.P. Ju, J.H. Chern Lin, Biomaterials 20 (1999) 21152122.

    [3] T. Grosdidier, M.J. Philippe, Mater. Sci. Eng. A291 (2000) 218223.

    [4] E. Takahashi, T. Sakurai, S. Watanabe, N. Masahashi, S. Hanada, Mater.Trans. 43 (2002) 29782983.

    [5] T. Maeshima, M. Nishida, Mater. Trans. 45 (2004) 10961100.[6] J.I. Kim, H.Y. Kim, H. Hosoda, S. Miyazaki, Mater. Trans. 46 (2005)

    851857.[7] H.Y. Kim, Y. Ohmatsu, J.I. Kim, H. Hosoda, S. Miyazaki, Mater. Trans. 45

    (2004) 10901095.[8] H. Hosoda, Y. Fukui, T. Inamura, K. Wakashima, S. Miyazaki, K. Inoue,

    Mater. Sci. Forum 426432 (2003) 31213125.[9] Y. Fukui, T. Inamura, H. Hosoda, K. Wakashima, S. Miyazaki, Mater. Trans.

    45 (2004) 10771082.[10] T. Inamura, Y. Fukui, H. Hosoda, K. Wakashima, S. Miyazaki, Mater. Trans.

    45 (2004) 10831089.[11] H.Y. Kim, H. Satoru, J.I. Kim, H. Hosoda, S. Miyazaki, Mater. Trans. 45

    (2004) 24432448.[12] J.I. Kim, H.Y. Kim, T. Inamura, H. Hosoda, S. Miyazaki, Mater. Sci. Eng.

    A A403 (2005) 334339.[13] H.Y. Kim, S. Hashimoto, J.I. Kim, T. Inamura, H. Hosoda, S. Miyazaki,

    Sci. Eng. A A417 (2006) 120128.[14] H.Y. Kim, T. Sasaki, K. Okutsu, J.I. Kim, T. Inamura, H. Hosoda, S.

    Miyazaki, Acta Mater. 54 (2005) 423433.[15] D.L. Moffat, D.C. Larbalestier, Metall. Trans. A 19A (1988) 1687

    1694.

    Effect of thermo-mechanical treatment on mechanical properties and shape memory behavior of Ti-(26-28)at.% Nb alloysIntroductionExperimental procedureResults and discussionConclusionsAcknowledgmentsReferences

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