Martensitic Transformation Stability And Shape Memory Effect Of Ti-Ta-Cu Alloys

This study systematicly researches the microstructure, martensitictransformation and shape memory effects of Ti68Ta32-xCux(x=0，3，6，9，12，15)alloys are investigated by optical microscopy, SEM, XRD and bending experimentto clarify the effects of Cu doping and aging on the constitution of phase,martensitic transformation stability, one-way and two-way shape memory behavior.The results show that the addition of Cu has an obvious influence onmicrostructure and phase constitution of Ti-Ta alloys. The Ti68Ta32-xCuxalloy isconsisted of single α” martensite phase with apparent pine-tree crystal when thecontent of Cu is less than9at%. When the content of Cu reaches12at%, the secondphase of the tetragonal Ti2Cu is discovered and mainly distributed at grainboundaries. Aging have no obvious influence on the microstructure of the α”martensite phase, but aging can induce a small amount of the Ti2Cu phase at grainboundary. The amount of the phase is increased with the decrease of agingtemperature and the increase of aging time.The doping of Cu has an obvious effect on the transformation temperatures ofTi-Ta alloys. The martensitic transformation temperatures increase with the increaseof Cu content. The decrease of transformation temperature caused by aging in thetemperature from473to673K can be ascried to the occurrence of ω phase whichleads to the decrease of Ti content. The content of ω phase increases with the rise ofaging temperature and prolonging of aging time. Termal cycling leads to thedecrease in transformation temperature. The doping of Cu and aging improves themartensite transformation stability. The degree in the reduction of is decreased andthe cycle number of the tendency to stability is decreased.The Cu doping enhances the shape memory effect of Ti-Ta alloys. Therecoverable strain increases with the increase of Cu content. When the Cu content is3at%, the recoverable strain is2.75%. When the Cu content is further increased, therecoverable strain is decreased. Aging improves the shape memory effect of theTi68Ta32-xCuxalloys. Recoverable strain is increased with the rise of agingtemperature. After aging at673K,2h，recoverable strain is up to3.47%. Thetwo-way shape memory effect is improved when the prestrain is increased. When the prestrain is5.5%, the two-way recoverable strain is0.63%. The Ti68Ta32-xCuxalloys do not show two-way shape memory effect under the condition of aging at473~673K for2h, but it reappears after aging at673K for10h. Two-wayrecoverable strain firstly decreases and then becomes stable with increase ofthermal cycling number. The doping of Cu leads to the decrease in the reduction oftwo-way recoverable strain and cycling number of the tendency to stability.