Superplasticity of Intermetallic Compounds

Abstract

Intermetallic compounds are superior to conventional metallic materials primarily because of their high-temperature strength parameters. The enhancement of these properties in the transition from metals to intermetallics is due to the change of the interatomic bonding as well as to a more complicated crystal structure. For example, in intermetallics, strong covalent bonds between the atoms provide a higher cohesive strength [9.1–5]. The more complicated crystal structure results in the growth of the elementary cell size, reduction of the symmetry and growth of the Burgers vector, which in turn lead to an increase in the Peierls stress and limit the number of active slip systems. These are the reasons why the majority of intermetallics are low-plasticity materials. In ordered intermetallic compounds, deformation is accomplished through the motion of superdislocations consisting of superpartial dislocations separated by a planar defect, i.e., an antiphase boundary [9.6]. Contrary to metals and disordered alloys where the slip plane is determined by the value of the Peierls forces or by the possibility of crystallographic splitting of the slipping dislocations, another criterion determines the slip plane choice. This is the energy of an antiphase boundary created during the motion of superdislocations in this plane. The anisotropy of the antiphase boundary energy can impede the process of cross slip and even slow down the motion of superdislocations [9.1–3,5]. These features provide for the enhanced high-temperature strength and heat and corrosion resistance of intermetallics and make their application as high-temperature structural materials rather promising.