We study the diffusion anisotropy (DA) of point defects in fcc and bcc metals in the presence of an applied biaxial stress. The DA depends sensitively on both the crystalline structure and the crystallographic direction in which the stress is applied. For example, interstitials in fcc metals diffuse faster in the plane of the compressive stress than normal to it when the stress is applied to the (001) plane, but they diffuse slower in-plane than out-of-plane when the stress is applied in the (111) plane. In contrast, an applied biaxial stress in the (001) plane of a bcc metal does not cause DA. These results can be explained by considering the interaction of the defects at their saddle point configurations with the external field, together with the constraints imposed by the crystal structure on the defect jump directions. Our calculations show that the DA can be large and lead to surprising results in a number of practical situations.
Bibliographical noteFunding Information:
We are grateful to Dr. P. Ehrhart for useful discussions. This research is supported by the U.S. National Science Foundation under Grant No. DMR-0419840 and in part by the U.S. Department of Energy, Basic Energy Sciences under Grant No. DEFG02-05ER46217.