Published online by Cambridge University Press: 22 February 2011
Slip in <111> directions is a deformation mode found in many intermetallic compounds ordered into the B2 (CsCl) structure, but in NiAl it is active only under the limiting conditions of uniaxial loading along <100> and low testing temperatures. This paper investigates the deformation characteristics of <100> oriented NiAl tested between 4.2K and 300K. Compression tests have shown that below about 100K, deformation takes place by slip in <111> directions without kinking, whereas between 100K and 300K kinking in the form of shearing on {100} becomes the dominant mode of plastic deformation, occurring usually near one or both ends of the compression samples. The yield stress has been found to exhibit a normal decrease with temperature, but at a rate that is smaller than most bcc metals. The sensitivity of the flow stress to strain-rate changes is also characteristically small, giving activation volumes around b3, b being the Burgers vector of a<111> superdislocation. Both slip line observations and transmission electron microscopy have shown slip mainly on {110} near 80K, but with increasing activity on {112} and cross-slip between {110} and {112} with the lowering of temperature to 4.2K.