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Yu M.,Xian Siwei Metal Material Co. | Yu M.,Xian Saite Metal Materials Development Co. | Niu Z.,Xian Siwei Metal Material Co. | Niu Z.,Xian Saite Metal Materials Development Co. | And 5 more authors.
Xiyou Jinshu/Chinese Journal of Rare Metals | Year: 2013

Processing maps of Ti-50.9Ni shape memory alloy under different strains and instability criteria were researched by employing dynamic materials model. The results indicated that the strain affected the processing map of Ti-50.9% Ni(atom fraction) shape memory alloy enormously, and the unstable domain of hot working of Ti-50.9% Ni shape memory alloy rose with the increase of the strain, spreading from low temperature and high strain rates area to high temperature and low strain rate area. In the domains with temperature ranging from 700 to 800°C, the strain rates ranging from 0.001 to 0.010 s-1 and temperature ranging from 800 to 950°C, strain rates ranging from 0.005 to 0.030 s-1, the efficiency of power dissipation η were all more than 40% when true strain was less than 0.6, which were the domains suitable for hot deformation of Ti-50.9Ni shape memory alloy. The efficiency of power dissipation and unstable domain based on Murty's instability criteria and Prasad's instability criteria had a similar distribution, and the hot working unstable area of Ti-50.9% Ni shape memory alloy conformed by Prasad's instability criteria was much larger. The stable deformation area conformed by Malas' instability criteria was much different compared with the two proposed before, and the stable hot working deformation domain of Ti-50.9% Ni shape memory alloy laid in the region of medium temperature and strain rate.

Yu M.,Xian Siwei Metal Material Co. | Niu Z.,Xian Siwei Metal Material Co. | Mao J.,Xian Siwei Metal Material Co. | Xue S.,Xian Siwei Metal Material Co. | Jia B.,Xian Siwei Metal Material Co.
Xiyou Jinshu/Chinese Journal of Rare Metals | Year: 2015

Through vacuum induction melting, the shape memory alloy Ti-50.9Ni (%, atom fraction) ingots were prepared. Cold drawing with different deformations was employed to the annealed Φ2.0 mm wire produced successively by forging, rolling and hot drawing. The cold drawn wires were then annealed between 500~800℃. The work hardening rate and recrystallization of cold drawn Ti-50.9Ni alloy were studied by tensile testing, X-ray diffraction (XRD) and optical microscope (OM). The rules of cold drawing hardening rate and the effects of anneal temperatures on the microstructure were obtained. The results indicated the working hardening rate of Ti-50.9Ni alloy was high, and the average value could reach above 20 MPa·%-1. Besides, the dσb/dε curve was divided into three zones. With the increase of cold drawing, dσb/dε firstly decreased, then rose and finally decreased. The maximum dσb/dε appeared when the true strain was 0 and 0.27, respectively, resulting from the appearance, growing up and intertwining of martensite, and the varying quantity of martensite with cold deformation. The recrystallization of fiber microstructure of fully cold drawn Ti-50.9Ni alloy emerged when annealed at 600℃(about 0.55Tm). When annealed at 700℃, the recrystallized grains grew up. The critical deformation of Ti-50.9Ni alloy which could cause recrystallization was between 10%~20%. Therefore, the annealing temperature of cold drawn Ti-50.9Ni shape memory alloy should be selected appropriately in the range of 600~700℃. ©, 2015, Editorial Office of Chinese Journal of Rare Metals. All right reserved.

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