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合金的形状记忆效应是以热弹性马氏体转变为基础,通常要求该类合金具有较大的热弹性马氏体可逆转变量和稳定的特征转变温度。但是,这些参数与热处理条件密切相关,特别是在M_s高于室温的三元Cu-Zn-Al形状记忆合金中存在着热弹性马氏体的稳定化现象。作者曾研究了Cu-14.84Zn-7.75Al(wt％)形状记忆合金在单分级淬火条件下的热弹性马氏体转变行为,并探讨了热弹性马氏体稳定化机理。本文用直流电阻法、金相显微镜、扫描电镜、X-射线衍射等方法继续对该合金在双分级淬火条件下的热弹性马氏体转变行为进行了研究。主要结果如下: (1)本实验合金经(360℃,2分钟+150℃,2分钟)双分级淬火可获得最大热弹性马氏体可逆转变量和稳定的特征转变温度,但双分级淬火在360℃停留时会使贫溶质原子α相在原β相晶界和晶内析出,导致基体相中溶质原子富化。随着360℃停留的时间延长,α相逐渐增多,热弹性马氏体可逆转变量和特征转变温度(M_s,M_f,A_s,A_f)分别逐渐减少和降低。当基体相完全分解成多相组织时,其热弹性才完全消失。 (2)在T_s高于340℃的单分级淬火试样中热弹性马氏体的稳定化,不是由于母相中第二相析出所造成。 (3)双分级淬火试样的热弹性马氏体可逆转变量减少和特征转变温度降低是因为在360℃停留时析出了贫溶质原子α相和基体溶质原子富化所造成。
The shape memory effect of the alloy is based on the thermoelastic martensitic transformation, which usually requires that the alloys have larger thermoelastic martensitic reversible transformations and stable characteristic transition temperatures. However, these parameters are closely related to the heat treatment conditions. In particular, there is a thermoelastic martensite stabilization phenomenon in a ternary Cu-Zn-Al shape memory alloy with M_s higher than room temperature. The authors have studied the thermoelastic martensitic transformation behavior of Cu-14.84Zn-7.75Al (wt%) shape memory alloy under single-stage quenching conditions and discussed the mechanism of thermoelastic martensite stabilization. In this paper, the thermo-elastic martensitic transformation behavior of the alloy under two-stage quenching was studied by direct current resistance method, optical microscope, scanning electron microscopy and X-ray diffraction. The main results are as follows: (1) The maximum thermoelastic martensitic reversible transformation and the stable transition temperature were obtained by double-stage quenching (360 ℃, 2 min + 150 ℃, 2 min) When staying at 360 ° C, the α phase of lean solute atoms will be precipitated in the original β phase boundary and in the crystal, resulting in enrichment of solute atoms in the matrix phase. With the prolonged residence time at 360 ℃, the α phase gradually increased, and the reversible transformation of thermoelastic martensite and the characteristic transition temperature (M_s, M_f, A_s, A_f) decreased and decreased respectively. When the matrix phase completely decomposed into multi-phase structure, its thermal elasticity completely disappeared. (2) The stabilization of the thermoelastic martensite in single-stage quenched specimens with T_s above 340 ° C is not due to the precipitation of the second phase in the parent phase. (3) The reduction of thermoelastic martensitic reversible transformation and the decrease of the characteristic transition temperature of double-grade quenched samples are due to the precipitation of the α-phase of lean solute atoms and the enrichment of matrix solute atoms at 360 ℃.