随着微米及纳米级尺度的金属器件的广泛使用，理解这个尺度下的力学性能与微观组织之间的联系（尤其是塑性变形过程中微观组织结构的演化），显得越来越为迫切。一般来说，金属材料在室温下的塑性变形主要通过位错滑移来完成，但孪生也是另外一种重要的塑性变形机制。目前在微米及纳米尺度下的塑性变形研究主要集中在位错机制上，所以为了进一步完善该尺度下的塑性变形理论，本项目将对该尺度下变形孪晶的形成机理进行系统性研究。因为TWIP钢具有面心立方晶体结构以及具有很低的层错能，在室温下变形非常容易产生变形孪晶，所以本项目将采用一种典型的TWIP钢作为本项目的模型材料进行研究。本项目将首先利用聚焦离子束技术制备微纳米级别的单晶圆柱样品，接着用纳米压痕来进行压缩试验，并利用透射电子显微镜来观察变形过程中孪晶的形成规律，以及建立相应的物理模型用于预测孪晶形成所需的临界切应力以及孪晶对应力-应变曲线的影响。

With the recent increasing use of micro/nanometre-size metallic materials in technological applications, there are strong needs to understand the microstructure-property relationship in these small-sized materials, especially the evolution of microstructure during plastic deformation. In general, plastic deformation of metals at room temperature can occur via dislocations. Nevertheless, deformation twinning is another important deformation mode. Most of the current research on micro/nanometre-sized metallic materials only focus on dislocation-mediated deformation. The present project employes a typical TWIP steel,which can form easily deformation twins at room temperature due to its low stacking fault energy, as a model material to study the formation of deformation twins in micro/nanometre-sized materials. Focus Ion Beam will be used to fabricate the micro/nano pillars, which will be then subjected to compression test by nanoindentation equiped with a flat punch. Then, TEM will be employed to investigate the deformation twins. Physically-based models will be established to predict the critical shear stress for the nucleation of deformation twins and to describe the effect of deformation twins on stress-strain curves.