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NiTi合金的形状记忆效应与其微观结构特征密切相关,中子衍射技术可以在力学加载过程中原位观察块体NiTi合金的相变、晶间应变以及孪晶再取向等演化特征.结合两相NiTi合金宏观应力-应变曲线呈现的四种阶段性变形特征,利用原位中子衍射技术对其变形过程中的微观结构演化进行了分析.奥氏体初始体积份额约22%,在低应变硬化阶段,晶面(110)B2和(002)B19′的应变分别突然减小和增大表明出现了应力诱发马氏体相变,奥氏体体积份额迅速减小,产生了011Ⅱ型孪晶;同时初始马氏体也开始发生再取向,随着应变量的增加,开始出现新的{20ī}型马氏体孪晶,这种孪晶引起的应变卸载时不能回复.在高应变硬化阶段孪晶变形起主导作用,衍射峰半高宽变化较小;而在应变硬化饱和阶段则以滑移机制为主,大量位错的产生使衍射峰半高宽显著增加.
NiTi alloy shape memory effect and its microstructure characteristics are closely related to the neutron diffraction technology can be observed in situ during the mechanical loading NiTi bulk phase transition, intergranular strain and twin re-orientation and other evolution characteristics.Combined with two-phase NiTi alloy Macroscopic stress-strain curve shows four stages of deformation characteristics, the use of in situ neutron diffraction technique to analyze the evolution of microstructure during the deformation of austenite initial volume share of about 22%, in the low strain hardening stage, The sudden decrease and increase of strain of (110) B2 and (002) B19 ’respectively indicate that stress-induced martensitic transformation occurs and the volume fraction of austenite decreases rapidly, resulting in 011Ⅱ type twins. At the same time, The martensite also began to reorientate with the increase of the amount of strain, new martensite twins began to appear, which could not be repaired by strains induced by twins. In the high strain hardening stage, twin deformation Plays a leading role in diffraction peak FWHM less change; while in the stage of strain hardening is the slip mechanism, a large number of dislocations make the diffraction peak full width at half maximum significantly increased.