Effect of α₂ lamellars slip systems on yield stress of polysynthetically twinning crystals for γ-TiAl

An analytical micromechanical method, based on the lamellar microstructure, dislocation slip and twinning deformation mechanisms of polysynthetically twinned crystal (PST), was proposed to investigate the yielding stress change as function of loading angle(θ) between the load axis and the lamellar boundaries and some influence parameters for a PST crystal. The effects of prism and pyramidal slip systems in α₂ lamellars on the yield stress of polysynthetically twin crystals of TiAl were analyzed. The simulation and analyses results indicate that, when θ = 0°, the slip is activated to cross the lamellar boundaries and the prism systems in α₂ phase are activated. When θ = 45°, the slip occurs parallel to interlamellar boundaries. When θ = 90°, the twinning in y phase are actived to cross the lamellar boundaries and the pyramidal slip systems in α₂ phase are not actived due to much higher critical resolved shear stress on the pyramidal planes. The rate of critical shear stress (CRSS) for twinning to ordinary slip, prism to twinning and pyramidal to prism can be described as k : e : z = 1 : 3 : 18.