Dislocations, kink bands, and room-temperature plasticity of Ti3SiC2

Transmission electron microscopy (TEM) of aligned, macrograined samples of Ti3SiC2, deformed at room temperature, shows that the deformed microstructu re is characterized by a high density of perfect basal-plane dislocations w ith a Burgers vector of 1/3[11 (2) over bar 0]. The dislocations are overwh elmingly arranged either in arrays, wherein the dislocations exist on ident ical slip planes, or in dislocations walls, wherein the same dislocations f orm a low angle grain boundary normal to the basal planes. The arrays propa gate across entire grains and are responsible for deformation by shear. The walls form as a result of the formation of kink bands. A dislocation-based model, that builds on earlier ideas proposed for kink-band formation in he xagonal metallic single crystals, is presented, which explains most of the microstructural features. The basic elements of the model are shear deforma tion by dislocation arrays, cavitation, creation of dislocation walls and k ink boundaries, buckling, and delamination. The delaminations are not rando m, but successively bisect the delaminating sections. The delaminations and associated damage are contained by the kink boundaries. This containment o f damage is believed to play a major role in endowing Ti3SiC2 and, by exten sion, related ternary carbides and nitrides with their damage-tolerant, pro perties.