In situ neutron diffraction evidence for fully reversible dislocation motion in highly textured polycrystalline Ti2AlC samples

Abstract

Herein careful analysis of in situ neutron diffraction patterns obtained, while cyclically loading highly textured polycrystalline Ti2AlC, a MAX phase, samples, provides compelling experimental evidence – in the form of fully reversible peak lattice elastic strain loops and peak widening and narrowing upon load cycling – for the existence of fully reversible dislocation motion. A comparison of the measured and calculated dislocation densities clearly shows that dislocation pileups alone cannot account for the experimental observations. Another micromechanism needs to be invoked. Based on the propensity of the MAX phases to deform by kinking, the micromechanism proposed is either the nucleation and annihilation of incipient kink bands, IKB, and/or the bowing of dislocations in preexisting low angle kink boundaries, LAKB. This micromechanism plays a vital role during the initial deformation of layered and other plastically anisotropic solids such as hexagonal close-packed metals. Consequently, the ramifications of this work on geology, metallurgy and other fields will prove quite important.