NiTi形状记忆合金的热变形行为及热加工图

Hot deformation behavior and processing map of NiTi shape memory alloy

为了获得镍钛形状记忆合金塑性加工最佳工艺参数,采用等温压缩实验研究了名义成分为Ni_(50.9)Ti_(49.1)(原子分数)的形状记忆合金在温度为600~1 000℃和应变为0.001~1 s_(-1)条件下的变形行为,并基于动态材料模型构建了该合金的热加工图。结果表明,当应变速率一定时,Ni_(50.9)Ti_(49.1)合金的流变应力随着变形温度的升高而减小;而当变形温度一定时,流变应力随着应变速率的增大而增大。Ni_(50.9)Ti_(49.1)合金的高η值区域随着真应变的增大而逐渐减小,且该Ni_(50.9)Ti_(49.1)合金的热变形失稳区随着真应变的增大而增大,这说明材料的热加工性能随着变形程度的增大而变差。Ni_(50.9)Ti_(49.1)合金的最佳热加工区域为具有高η值的稳定加工区,即温度为700~950℃,应变速率为0.005~0.05 s_(-1)。

In order to obtain the optimal process parameters of NiTi shape memory alloy during plastic working,based on isothermal compression test,hot deformation behavior of Ni（50.9）Ti（49.1）（ mole fraction） shape memory alloy was investigated at the temperatures ranging from 600 ℃ to 1 000 ℃ and at the strain rates ranging from 0.001 to 1 s^-1. Furthermore,processing map was established on the basis of the dynamic material model. The results indicate that at a given strain rate,the flow stress of Ni（50.9）Ti（49.1）alloy decreases with the increase in the temperature,whereas in the case of a constant deformation temperature,the flow stress of Ni（50.9）Ti（49.1）alloy increases with the increase in the strain rate. The region where Ni（50.9）Ti（49.1）alloy possesses high η value decreases with the increase in the true strain. In addition,the instability region of Ni（50.9）Ti（49.1）alloy during hot deformation increases with the increase in the true strain,which indicates that the hot workability of Ni（50.9）Ti（49.1）alloy decreases with the increase in the deformation degree. The optimal region in which Ni（50.9）Ti（49.1）alloy is subjected to hot working is determined as the one which possesses high η value,where the temperature lies between 700 ℃ and 950 ℃,and the strain rate ranges from 0.005 s^-1 to 0.05 s^-1.