Dislocations in B2 ordered alloys

Abstract

Intermetallic compounds are currently the subject of considerable research effort because of their possible structural applications, particularly at high temperature. The B2 structure, sometimes called L20, ordered body-centered cubic or CsCl-type, is the simplest ordered structure an AB-type compound can adopt. Nevertheless, three different dislocation Burgers’ vectors are found, namely <100>, <110> and <111>, depending on the compound and the temperature of deformation. Only <100> and <111> are normally observed at lower temperatures. For example, figure 1 shows <100> slip in PdIn and <111> slip in FeAl. An important practical difference between <111> and <100> slip is that the latter provides only three independent slip systems and, thus, can lead to only limited general plastic flow in a polycrystal.At low temperature, why <100> or <111> slip occurs is not wholly clear, although there have been several attempts at rationalizing the experimentally observed slip vectors. Rachinger and Cottrell made the first attempts at rationalization when they used a nearest-neighbor model to estimate a critical ordering energy above which <100> slip would operate and below which <111> slip was presumed to occur.