Thermal deformation behavior of Ni60Ti40 shape memory alloy
MA Xin1, XU Si-yang1, ZHOU Ge2, DING Hua1,3
1. School of Materials Science and Engineering, Northeastern University, Shenyang 110819, Liaoning, China; 2. School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110870, Liaoning, China; 3. Key Lab of Lightweight Structural Materials of Liaoning Province, Shenyang 110819, Liaoning, China
Abstract：To obtain optimum conditions of Ni60Ti40 shape memory alloy during hot deformation, the thermal deformation behavior at 800-1 000 ℃ and strain rate 0.005-5.000 s-1was studied by isothermal compression experiment with constant strain rate. The constitutive relationship of Ni60Ti40 alloy was established by exploring the effect of different conditions on the rheological behavior, and the processing maps were constructed based on the dynamic material model. As the results showing, the flow stress of Ni60Ti40 alloy decreases with the increase of deformation temperature and increases with the increase of strain rate. When the compression test involving the wide temperatures of 900-1 000 ℃ and strain rates of 0.005-0.500 s-1, the flow stress reaches the steady state quickly, and requires less deformation. The flow stress constitutive model of Ni60Ti40 alloy hot deformation constructed using Arrhenius hyperbolic sinusoidal model can basically predict actual flow stress variations with process parameters accurately, and the average activation energy of Ni60Ti40 hot deformation is 213 kJ/mol. During hot deformation of the Ni60Ti40 alloy, three stable deformation area and one instability area are confirmed in the processing maps. The suitable deformation domains are 800-870 ℃/0.005-0.080 s-1, 870-950 ℃/0.080-0.500 s-1 and 950-1 000 ℃/0.050-5.000 s-1. The range of instability area that should be avoided during hot working is 800-850 ℃/0.220-5.000 s-1.
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2022, Vol. 32 
