Compressive flow stress of a binary stoichiometric Ni 3Al single crystal

Abstract

N4Al exhibits the yield stress anomaly, i.e. its flow stress increases with increasing temperature (1,2). The yield stress anomaly has been extensively studied using single crystals (3-8). These studies have been carried out on Ni-rich (3) or ternary Ni3Al (4-8), whereas the mechanical properties of a binary stoichiometric Ni3Al single crystal that do not contain ternary additions have never been evaluated. Since deviations from stoichiometry or ternary elements essentially produce point defects, the nature of the yield stress anomaly can be affected by these. Therefore it is worth studying N&Al deformation mechanisms using a binary stoichiometric single crystal. However, there is a difftculty in growth of these crystals due to the peritectic reaction liquid + NiAl + NisAl (l), by which the intermetallic forms in a binary alloy. The peritectic solidification process usually leads to copious grain nucleation. Thus all the single crystals grown to date have contained ternary additions or have deviated towards the Ni-rich side of stoichiometry in order to avoid the peritectic reaction (9). Very recently we have found that large binary stoichiometric Ni3Al single crystals can occasionally be grown using a floating zone (FZ) method (lo- 12). The present paper reports the orientation depend- ence of the compressive flow stress of such crystals at 293-1273 K for testing axis between [OOl] and [Oll].