GRAIN-SCALE DEFORMATION MECHANISMS IN AN ADDITIVELY MANUFACTURED ALUMINIUM BRONZE OLIGOCRYSTAL

Abstract

Oligocrystals provide a unique material for in-depth analysis of deformation mechanisms in metals and alloys. In this paper, the deformation mechanisms in a Cu-7.5 wt.% Al oligocrystal are investigated experimentally and numerically. An experimental sample containing several coarse columnar grains is produced by wire-feed electron-beam additive manufacturing. Based on the experimental data, a crystal plasticity finite element model is built to consider realistic grain shape and orientations. This study involves a comprehensive analysis of experimental data, numerical results and analytical estimates to reveal the peculiarities of slip activation in oligocrystal grains under compression. Experimental and numerical findings have shown that along with slip systems with the highest Schmid factors, other slip systems are activated in most grains to accommodate their plastic deformation. To elucidate why the slip systems with non-maximal Schmid factors became active, we examined the stress fields within the grains. It was revealed that the stress state at the grain scale deviated from uniaxial. Finally, a detailed numerical analysis of strain rate dynamics demonstrated that plastic deformation in particular grains developed in the form of narrow fronts. These fronts periodically generated near the moving punch and subsequently propagated towards the opposite side of the sample. The study has shown that oligocrystal analysis provides valuable insights into the linkage between the intra- and intergrain deformation mechanisms with the overall material behaviour.