Dislocation microstructures in boron-doped Ni3Al

Despite its relative engineering eclipse (at least in aeronautical terms), Ni3Al is still a rewarding area for scientific research, primarily because so much is already known about it. Many of its mechanical properties, however, are still not understood in terms of secondary defect populations and behaviour. For example, the fundamental Kear-Wilsdorf mechanism, wherein cross slip from {111} to {100} planes provides an increase in strength with temperature, has received intensive microscopic scrutiny recently, and it now appears that the movement of the superpartials on {100} is far more than the atom spacing or so envisaged in Paidar et al. Whether delocking occurs, however, and if so how often, is still not clear. Examples of other problems which remain are:a) What are the relative contributions to work hardening of the Kear-Wilsdorf mechanism, APB tube formation and SISF formation?b) Although the yield stress increases with temperature it also increases slightly with strain rate, whereas a negative strain rate dependence might have been expected.