ScriptaMaterialia, Vol. 37, No. 11, pp. 1777-1782,1997 Elsevier Science Ltd PI1S1359-6462(97)00339-4 Copyright 0 1997 Acta Metahrgica Inc. Printed in the.USA. All rights reserved 1359~6462197$17.00 + .OO COMPRESSIVE FLOW STRESS OF A BINARY STOICHIOMETRIC N&Al SINGLE CRYSTAL D. Golberg*, M. Demura, and T. Hirano Nat ional Research Institute for Metals, l-2-1 Sengen , Tsukuba, Ibaraki 305, Japan *Present address: National Institute for Research in Inorganic Materials, l- 1 Namiki, Tsukuba, Ibaraki 305, Japan (Received June 17, 1997) (Accepted August 5, 1997) Introduction 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]. Experimental Procedure A binary stoichiometric Ni-25 at.%Al alloy was arc-melted using 99.9999%Al and 99.97% Ni. The seed and feed ‘crystals were prepared from the same arc-melted rod. The procedure for crystal growth has been previously reported by us (lo- 12). Single crystals of length 160- 170 mm and diameter IO- 12 mm were grown. Al-content of the as-grown crystal was measured by using wet chemical method and was found to be slightly Al-rich, i.e., 25.2 at.%Al, with respect to stoichiometry. 1777