The mechanics of slip transition at intermediate temperatures in <001>-oriented NiAl single crystals I. Experimental observations of the decomposition of α<111> dislocations in Ni–44 at.% Al

Abstract

Ni–44 at.% Al single crystals were studied after compressive deformation along the hard orientation between 700 and 825 K. In order to understand the mechanism of the slip transition occurring at intermediate temperatures, compression was performed at various strain rates and to various strain levels. Local decomposition of α<111> dislocations was observed between 750 and 800 K. At 800 K (the slip transition temperature), complete decomposition occurs into α<101> and α<010> dislocations. Several unique features are associated with this decomposition event, such as the preference for near-edge line directions (for the α<111> dislocations), significant strain softening between 800 and 900 K, and the effect of thermal activation in determining the extent of the actual decomposition event.