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Influence of strong grain size effect on deformation twins

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Document pages: 17 pages

Abstract: Deformation twins 1,2,3,4,5,6 in crystals are a highly coherent inelastic shear process, which controls the mechanical behavior of many materials, but their origin and spatio-temporal characteristics are shrouded in mystery. Through micro compression and in-situ nano compression experiments, we find that the stress required for deformation twins increases sharply with the decrease of the size of titanium alloy single crystal sample 7,8 until the sample size is reduced to one micron. Below this size, the deformation twins are completely deformed by ordinary dislocation plasticity with small correlation. With the transformation of deformation mechanism, it is observed that the maximum flow stress of submicron cylinder is saturated at a value close to the ideal strength 9,10 of titanium. We develop ‘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 dependence11,12,13,14,15,16,17 relevant for applications.

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