Some features of the formation and destruction of dislocation barriers in intermetallic compounds: IV. Thermoactivated straightening of dislocations along a preferred direction in TiAl

Abstract

As a result of experiments which include plastic deformation and subsequent heating without stress, self-blocking of dislocations in TiAl has been revealed. The transformations of glissile dislocations into dislocation barriers has been observed both for superdislocations with Burgers vectors <101] and 1/2<112] and for single dislocations. The preliminary deformation was performed at room temperature; the heating without stress, at temperatures both below and above the peak temperature T max in the temperature dependence of the yield stress σy(T). With a proper choice of the temperature of heating and its duration, it proved to be possible to fix the initial stages of the straightening of single dislocations along a preferred direction parallel to their Burgers vector and the subsequent formation of long blocked dislocations. As a result of TEM analysis, it has been shown that the barriers were formed during heating without stress but they were not destroyed. It has been revealed that the barriers with a total Burgers vector <101] in TiAl, in contrast to Ni3Al, remain indestructible even when the experiments included a repeated deformation.