Grain Boundary-Mediated Lattice Reorientation in α-Titanium to Promote Plastic Deformation in Hard-Oriented Grains

摘要

A new deformation mode is revealed by atomistic simulations in titanium with hexagonal close packed structure. With the combination of soft-hard grains with a vertical grain boundary and tensile loading close to the hard orientation, plastic deformation initiates through soft-to-hard grain penetration instead of traditional mechanisms. Grain penetration proceeds by lattice reorientation of the hard grain with expansion and contraction along and perpendicular to the loading direction, respectively, accompanied by local atomic shuffling. Grain penetration is a nucleation process, triggered by stress mismatch and inhibited by surface tension from the soft-hard grain boundary. It is favored by large stress mismatch, e.g., at large strain or large volume fraction of the soft grain compared with the hard. Lattice reorientation provides relatively large normal strain of 8.3% with activation energy of 0.04 eV per atom, and hence is expected to be an efficient mechanism to accommodate plastic deformation along the hard orientation, e.g., within the microtexture during cold dwell fatigue.