Role of interfaces in deformation and fracture: Titanium aluminides

摘要

Available experimental data on deformation and fracture behavior of polysynthetically twinned (PST) TiAl crystals are analyzed on the basis of the calculated results of bulk and defect properties and shear fault, cleavage and interfacial energies of TiAl and Ti(sub 3)Al. The extent of dissociation width of and ordinary dislocation is calculated to be larger at (alpha)(sub 2)/(gamma) and (gamma)/(gamma) interfaces by about two-fold as compared to the bulk of (gamma)-phase, suggesting the enhances slip along the interfaces when the crystal is a soft orientation. Propagation of (111) cleavage cracks is influenced by the mixed mode (II and III) of external loading applied to the coplanar deformation twinning and ordinary slip, leading to translamellar fracture. According to the calculated interfacial fracture energies, cleavage cracking si to occur on (alpha)(sub 2)/(gamma) boundaries and least likely on true-twin boundaries. Discussion is given on the roles of misfit dislocations, kinetics of dislocation-interface interactions and hydrogen embrittlement in deformation and fracture processes.