约束加热温度对NiTi合金显微组织的影响

Effect of Constrained-heating Temperature on Microstructure of NiTi Alloy

本文采用金相显微镜,x-射线衍射仪和透射电镜,研究了约束加热温度对近等原子比NiTi合金室温组织和微观结构的影响。结果表明:随约束加热温度的升高,合金的室温组织和微观结构将会发生明显的变化。低温约束加热时,合金的室温组织与未经约束加热时相同,由母相秈马氏体相组成,马氏体变体呈板条状,但经约束加热处理后,马氏体变体呈现出明显的方向性;较高温度约束加热时,室温组织由R相和马氏体相组成,并有位错亚结构存在,进一步提高约束加热温度,则其室温组织又由母相和马氏体相组成。文中对组织变化的原因进行了较详细的讨论,认为与约束加热时形成的内应力场有关。

The effect of constrained-heating temperature on the microstructure of martensite and R-phase in a near-equiatomic NiTi alloy has been studied by metalloscope, X-ray diffraction analysis, SEM and TEM. It is shown that the microstructure of the alloy can be remarkably under the influerce of the constrainedheating temperature.The microstructure is the same as that of the sample without constrained-healing at lower temperature and it is composed of parent phase and martensite at room temperature; the martensite variant is plate which is possessed of obvious direction ofter constrained-heating at lower temperature. The microstructure of the sample with constrained-heating at about 450℃ consist of R-phase and martensite with the dislocation forms. With increasing the constrained-heating temperature to 550℃, the microstructure is the same as that of the sample without constrained-heating. In present paper, the cause of the microsiructure difference has been discussed and considered that it is related to the different initial stress fields introduced by the constrained-heating in the parent phase.