Mechanisms of compatible deformation in NiAl-bicrystals

The compatibility of deformation in near-stoichiometric NiAl bicrystals was analysed above and below the brittle-to-ductile transition (BDT) of NiAl p olycrystals and correlated with the active deformation mechanisms. The bicr ystal configuration consisted of two specially arranged [110]-orientations and was chosen in such a way that the bicrystal had to deform incompatibly during uniaxial compression below the BDT due to the sole activity of [100] -slip. However, above the BDT the bicrystal deformed compatibly by activati on of a deformation mechanism in addition to [100]-slip. In the bicrystal b oundary region of the compatibly deformed bicrystals an adaptive deformatio n was clearly observed and correlated with pronounced orientation gradients as determined by single grain orientation measurements in a SEM. These wer e not observed during unconstrained deformation of a single crystal or in t he bicrystals far away from the boundary. A comparison with simulated orien tation changes led to the conclusion that the additional deformation mechan ism activated at the BDT consists of [110]{110}-slip, while [100]-climb, wh ich was discussed alternatively, had to be ruled out in this temperature re gime. However, a transition from [110]-slip to [100]-climb most probably oc curs at higher temperatures. In addition the analysis reveals a strong tend ency for latent hardening of [100]{100}-slip systems and also of [110]{110} -slip systems which decreases with increasing deformation temperature. (C) 1999 Elsevier Science Ltd. All rights reserved.