The plastic deformation behavior of monocrystals with a composition of 56at%Al was studied during compression, as a function of crystal orientation, at temperatures ranging from -196 to 1100C. It was found that the yield stress versus temperature curves for all of the orientations which were studied could be divided into 3 temperature regions. The yield stress decreased rapidly with increasing temperature at both low and high temperatures, and an anomalous increase in the yield stress was observed at intermediate temperatures; with a peak at 700 to 1000C (depending upon the crystal orientation). Both ordinary and <101] superlattice slip exhibited an anomalous increase in critical resolved shear stress. However, the extent of the anomaly which was associated with the former slip was much smaller than that for the latter slip. The critical resolved shear stress for <101] slip depended upon the crystal orientation. Within the anomalous temperature region, the critical resolved shear stress exhibited a very small strain-rate sensitivity and thermal reversibility. Superlattice dislocations with b = <101], in specimens which had been deformed in the anomalous temperature region, were usually aligned with their screw orientation and adopted a locked configuration. These features were very similar to those which were associated with the anomalous strengthening of Ni3Al. The critical resolved shear stress for ordinary slip was considerably larger than that for <101] superlattice slip at temperatures below 600C. This resulted in a limited orientation range for the operation of ordinary slip. In the anomalous temperature region, the strain-rate sensitivity of critical resolved shear stress for ordinary slip was also very small, and ½<110] dislocations with many cusps were seen to align themselves along their screw orientation. The dislocation mechanism of the anomaly for ordinary slip was suggested to be different to that for <101] superlattice slip. Above the peak temperature, <110] slip, twinning and <112] superlattice slip were found to be operating. Slip along <110] occurred not only on {111} but also on (001) and {110); depending upon the orientation. Twinning and <112] superlattice slip occurred only at certain orientations.

H.Inui, M.Matsumuro, D.H.Wu, M.Yamaguchi: Philosophical Magazine A, 1997, 75[2], 395-423