In-situ straining experiments in transmission electron microscopy were performed to investigate the propagation of crack,twinning and interaction of crack with twins. Lots of micro-twins were observed in the deformation band near the tip of crack. The stress is relaxed by the formation of micro-twins and the densely developed micro-twins prevent the growth of crack from the deformation band,subsequently the cracks extend into adjacent grains across grain boundaries,and grow along cleavage plane. Multiple twins are observed in hot-rolling AZ31 magnesium alloys,when cracks propagate into twins through twin grain boundaries(GBs),the direction of growth deviates. It is concluded that twins,especially multiple twins effectively baffle the development of crack.
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