中文摘要：

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合金宏观应力一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（011）II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{20i}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．

英文摘要：

It is well known that the shape memory effect of NiTi alloy is closely related to the micro-structural characteristics. Neutron diffraction method can be used to explore the changes of the phase transformation, lattice strain and twining reorientation of bulk NiTi alloy during deformation caused by the applied stress. In this paper, combining the four types of deformation characteristics in the macro stress-strain curves of dual phase NiTi alloy and using in-situ neutron diffraction measurement, the micromechanical interactions and phase transformation are determined. The volume fraction of the initial austenite before deformation is about 22%. The contrast transformation, which is corresponding to the lattice strain rapid decreasing of （110）B2 and increasing of （002）m9,, reveals that the stress-induced transformation from austenite to martensite phase appears with the volume fraction of austenite decreasing rapidly and （011） II type twinning increases at the low strain hardening stage. At the same time, the initial martensite grains change their orientation to a favorable direction and the new {201） type martensite twinnings induced with the increase of applied stress cannot recover after unloading. At the high strain hardening stage, the twinning deformation is considered to be the main mechanism from the observing of the changes in the full width at half maximum （FWHM）. Meanwhile, the slipping caused by dislocation is the main deformation mechanism corresponding to the obvious increas of the FWHM at the statured stage of the strain hardening.