Center for Advancing Materials Performance from the Nanoscale (CAMP-Nano), State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, 710049, China.
Nature. 2010 Jan 21;463(7279):335-8. doi: 10.1038/nature08692.
Deformation twinning in crystals is a highly coherent inelastic shearing process that controls the mechanical behaviour of many materials, but its origin and spatio-temporal features are shrouded in mystery. Using micro-compression and in situ nano-compression experiments, here we find that the stress required for deformation twinning increases drastically with decreasing sample size of a titanium alloy single crystal, until the sample size is reduced to one micrometre, below which the deformation twinning is entirely replaced by less correlated, ordinary dislocation plasticity. Accompanying the transition in deformation mechanism, the maximum flow stress of the submicrometre-sized pillars was observed to saturate at a value close to titanium's ideal strength. We develop a 'stimulated slip' model to explain the strong size dependence of deformation twinning. The sample size in transition is relatively large and easily accessible in experiments, making our understanding of size dependence relevant for applications.
晶体的形变孪晶是一种高度协调的非弹性剪切过程，控制着许多材料的力学行为，但它的起源和时空特征仍笼罩在神秘之中。使用微压缩和原位纳米压缩实验，我们发现钛合金单晶的变形孪晶所需的应力随样品尺寸的减小急剧增加，直到样品尺寸减小到一微米以下，在这以下，变形孪晶完全被相关性较小的普通位错塑性所取代。伴随着变形机制的转变，亚微米尺寸的柱子的最大流动应力被观察到在接近钛的理想强度的一个值处饱和。我们提出了一个“受激滑移”模型来解释变形孪晶的强烈尺寸依赖性。转变过程中的样品尺寸相对较大，在实验中很容易达到，这使得我们对尺寸依赖性的理解与应用相关。
