Effects of trapping dislocations within small crystals on their deformation behavior

Micron-sized metallic crystals are much stronger than their bulk counterparts. However, their deformation is jerky and they do not strain harden continuously, so that precise metal forming is difficult. This work demonstrates that coating or filling aluminum microcolumns with tungsten can eliminate these strain bursts and significantly increase the strain-hardening rate. A rule-of-mixtures analysis indicates that such improvements in the mechanical behavior of the composite micropillars are not due to the load-sharing effect of the incorporated tungsten phase. Transmission electron microscopy examination reveals that the coating or filling traps dislocations inside the crystals, thus raising the stored dislocation density by up to three orders of magnitude. This study indicates that microcrystals can be significantly strain-hardened and their deformation behavior can become more controllable when dislocations are confined inside them.