Single crystals of 44 or 50at%Al alloy were tested in compression in the hard <001> orientation. The dislocation processes and deformation behaviour were studied as a function of temperature, strain and strain rate. A slip transition typically occurred from a<111> slip to non-a<111> slip at intermediate temperatures. In 50at%Al crystals, only a<010> dislocations were observed above the slip transition temperature. In contrast, a<101>{101} glide was observed to control deformation beyond the slip transition temperature in the 44at%Al alloy. The a<101> dislocations were observed mainly along both <111> directions in the glide plane. High-resolution transmission electron microscopic observations showed that the core of the a<101> dislocations along these directions was decomposed into two a<010> dislocations; separated by a distance of approximately 2nm. The temperature window of stability for these a<101> dislocations depended upon the strain rate. At a strain rate of 1.4 x 10-4/s, a<101> dislocations were observed between 800 and 1000K. Complete decomposition of a<101> dislocations into a<010> dislocations occurred beyond 1000K; leading to a<010> climb being the deformation mode at higher temperatures. At lower strain rates, decomposition of a<101> dislocations was observed to occur along the edge orientation, below 1000K. Embedded-atom method calculations and experimental results indicated that a<101> dislocations had a large Peierls stress at low temperatures. Based upon the present microstructural observations and upon a survey of the literature with respect to vacancy content and diffusion in NiAl, a model was proposed for a<101>{101} glide in Ni-44at%Al, and for the observed yield strength versus temperature behaviour of Ni-Al alloys at intermediate and high temperatures.

Observations of Glide and Decomposition of a<101> Dislocations at High Temperatures in Ni-Al Single Crystals Deformed in the Hard Orientation. R.Srinivasan, M.S.Daw, R.D.Noebe, M.J.Mills: Philosophical Magazine, 2003, 83[9], 1111-35