High Strength and High Ductility in Nanostructured Aluminium-Based Intermetallics Produced by High-Pressure Torsion

Abstract

Aluminium-based intermetallics (aluminides) exhibit high strength, but low plasticity at room temperature. Despite approaches employed for improvement of their mechanical properties, there is a trade-off between the strength and the plasticity in intermetallics. In this study, several nanostructured aluminium-based intermetallics (AlNi, TiAl, Ni2AlTi) with ultrahigh compressive strength, up to 3.5 GPa, and high plasticity, up to 23%, are produced in situ from elemental powders by severe plastic deformation using high-pressure torsion (HPT) at 573 K and subsequent annealing at 673 or 873 K. It is shown that the high work-hardening behavior and plasticity in these intermetallics are due to (i) nanotwin formation, (ii) bimodal microstructure, and (iii) activation of different deformation mechanisms such as dislocation slip, twinning and grain boundary sliding. The diffusivity appears to increase by 12-22 orders of magnitude during HPT because of ultrahigh vacancy concentration and high dislocation density, which results in the formation of intermetallics at low temperatures.