Scripta METALLURGICA Vol. 8, pp. 1049-1054,1974 Pergamon Press, Inc. Printed in the United States THE ORIGIN OF DISLOCATIONS WITH b = <ii0> IN SINGLE CRYSTALS OF ~-NiAI COMPRESSED ALONG <001> AT ELEVATED TEMPERATURES Nestor J. Zaluzec and Hamish L. Fraser Department of Metallurgy and Mining Engineering and Materials Research Laboratory University of Illinois at Urbana-Champaign Urbana, Illinois 61801 (Received July 12, 1974) Introduction It is well known that the preferred set of slip systems in stoichiometric ~-NiAI involves glide of dislocations of b = <i00> on either [ii0} or {010} (e.g., 1-4). Clearly, when single crystals are deformed along <001>, little or none of the applied stress is resolved onto these preferred slip systems, and presumably some other type of slip system must be activated or another mechanism of plastic deformation must be invoked. Thus, it has been shown that between 77°K and 300°K, <001> single crystals deform by operation of <iii>[i12} and <iii>[ii0} (4). Between ~300°K and 1050°K, plasticity appears to be produced by either glide or a combination of glide and climb of dislocations of the type = ~I00>, depending on temperature and strain rate (5). Only very few dislo- cations of b = <ii0> were observed in that study, and it was assumed that they were the result of collision of two dislocations with b = <i00>. On the basis of these latter results, one would predict that at higher temperatures climb of dislocations of b = <I00> would become increasingly predominant. However, there are a number of reports that at temperatures above 1000°K, plastic deformation in C001> single crystals is produced by operation of <ii0>{ii0} (3,6-8). In these latter studies, two of the techniques that have been used to determine the active slip system are surface slip analysis and transmission electron micro- scopy (TEM). Recently, Wasilewski, Hutchings and Loretto (9) have shown that some care must be exercised in using surface offsets to deduce dislocation Burgers vec- tors. They have demonstrated that the offset on the surface of a crystal is not 1049