Thermomechanical strengthening of B2 intermetallics

Abstract

Intermetallic compounds have been extensively studied, due to their greater mechanical strength as compared to metals, especially when used at high temperature. However, their application as structural materials has been restricted by their poor ductility. This limited ductility at room temperature arises as a consequence of an insufficient number of, as well as difficult, dislocation slip systems. TiNi, otherwise known for its shape memory properties, exhibits not only significant room temperature ductility (40-50%) but also the ability to be thermomechanically strengthened. The B2 structure, present in TiNi alloys, provides for only three independent dislocation slip systems with dislocation Burgers vectors of the 〈100〉 type. However, concurrent mechanical twinning enables polycrystalline TiNi to fulfill the Von Mises strain compatibility requirements. Transmission electron microscopy is utilized to correlate the microstructure that develops during recovery and the increased combination of ductility and strength. Ternary alloy additions and processing conditions, which may induce mechanical twinning in other B2 intermetallic compounds (for example NiAl), will be discussed.