Ni-Ti形状记忆合金热压缩变形行为及本构关系

HOT DEFORMATION BEHAVIOR AND CONSTITUTIVE RELATIONSHIP OF Ni-Ti SHAPE MEMORY ALLOY DURING COMPRESSION AT ELEVATED TEMPERATURES

采用热模拟实验在变形温度为700—900℃、应变速率为10^(-3)—10~1s^(-1)的条件下,对Ni-Ti合金的热压缩变形行为及变形组织进行了分析.采用实测数据回归分析方法,得出双曲正弦函数形式本构方程中的材料参数;将材料参数对应变进行二次拟合,建立了Ni-Ti合金热变形过程的流变应力与变形温度、应变速率和应变的本构关系.变形激活能Q和结构因子A随应变的增加而减小,应力指数n随应变的增加呈线性增加.有序-无序间的相互转变以及动态回复或动态再结晶的综合作用,是Ni-Ti合金的热压缩变形真应力-真应变曲线变化规律不同于传统非金属间化合物材料的主要原因.

The hot deformation behavior of Ni-Ti alloy was studied by compressive deformation tests in the strain rate range of 10^-3-10^1 s^-1 and temperature rage of 700-900 ℃, and the associated structural changes were investigated by metallography and TEM. By using regression analysis methods based on measured data, the material parameters in the Arrhenius-type hyperbolic-sine equation were resolved, and then used to fit deformation strains. Based on the above analysis, a constitutive equation which related the flow stress to temperature, strain rate and strain was established. The activation energy, Q, and structure factor, A, decrease as the strain increases. However, the stress exponent, n, linearly increases with the increase of the strain. The main reasons that lead to the difference between the true stress-true strain curves of Ni-Ti alloy and non-intermetallic materials are the order-disorder reciprocal transition and dynamic recovery or dynamic recrystallization.