Slip Modes in B2-Type Intermetallic Alloys

Abstract

The slip systems reported in B2-type ordered intermetallic alloys are overviewed on the basis of energetic and kinetic aspects of dislocation motion. The large elastic shear anisotropy in most B2 alloys and its increase with increasing hypostoichiometry and decreasing temperature are indicative of a lattice instability, which leads to a {110}<110) displacive transformation, not slip deformation. The orientation dependence of the yield stress for <111> slip directions at low temperatures can be explained by the Peierls-Nabarro model modified by the anisotropic coupling effect of nonglide stress. Some other thermally activated mechanism must be responsible, however, for the yield behavior of B2 alloys at elevated temperatures. The <001> slip directions observed in NiAl and CoTi are best rationalized in terms of the APB energy concept. The importance of mobile dislocation density and dislocation multiplication mechanisms is emphasized. The reason why NiAl does not show the anomalous temperature dependence of yield strength while CoTi does is not clear, and further research efforts in this area are recommended. © 1990, The Japan Institute of Metals. All rights reserved.