Effect of indentation orientation on the onset of plastic deformation for a MAX phase Ti₂AlC

Polycrystalline Ti₂AlC alloys were prepared by spark plasma sintering of high purity elemental materials, and subsequently annealed at_ 1500℃ for 24 h. Nanoindentation behavior was studied on the grains with their surface normal directions parallel to 〈3362〉,〈4481〉,〈0001〉and〈1120〉. During loading of nanoindentation, popin events were found to occur for all the indentation directions. The critical loads of the first popin observed for the indentation directions parallel to〈1120〉and〈0001〉were higher than those for〈3362〉and〈4481〉. Surface topography around the residual indents suggests that the basal slip dominates the plastic deformation upon indentation. These results suggest that the nucleation of the basal dislocation is a major barrier for the onset of plastic deformation underneath the indenter.