An experiment on the transient behavior of Ni3Al, which had demonstrated that the anomalous flow stress was thermally reversible in the small-strain yielding regime, was repeated here. Specimens taken from a single crystal, which had orientations near to <001>, were pre-strained at 873K and then strained at 300K. The flow properties of this crystal were compared with those of a crystal which had been strained only at 300K. Both crystals were examined by using transmission electron microscopy. It was found that, in the small-strain flow regime, the flow stress anomaly was reversible. Pre-straining at a higher temperature before room-temperature deformation revealed little effect of the pre-straining during the yield transient; even though the transmission electron microscopic observations showed that many Kear-Wilsdorf locks were retained in the sub-structure. Microscopic examination also revealed the presence of a second dislocation structure, which was characteristic of low-temperature deformation, in selected regions of thin foils of the pre-strained sample. This observation required that some part of the sub-structure had to recover extremely rapidly, if not instantaneously, upon changing the temperature and/or unloading. It was suggested that future models had to consider the full behavior of all dislocation loop types and junctions types during a thermally reversible transition from the elastic regime, through the micro-strain regime, to plastic flow.

D.M.Dimiduk, T.A.Parthasarathy: Philosophical Magazine Letters, 1995, 71[1], 21-31