Concentration-Dependent High-Temperature Deformation Mechanism of Hexagonal Close-Packed Ti-Al Alloys

The dependence of Al alloying on the high-temperature deformation physics of Ti-Al alloys was investigated in the present study. The mechanisms of planar dislocation slip, enhanced < c + a > activity and stacking faults were operative in low-alloyed Ti-Al model materials upon plastic deformation at 600 degrees C. Increasing Al content up to 10.2 at. pct triggered significant pyramidal slip and 101 over bar 2 twins, highlighting the role of Al alloying. Atomic-scale characterization revealed the nature of the topologically discontinuous "stepped" twin boundary, consisting of alternately stacked basal/prismatic interface couples without a traditional rigorous twin invariant plane. This is the first time significant twinning has been observed in severely alloyed polycrystalline hcp metallic alloys, especially plastically deforming at 600 degrees C with a low strain rate of 1 x 10(-4) s(-1). A lattice-reorientation-based twinning mechanism, as well as its influence on mechanical properties, was proposed and discussed.