The eŒect of stress on point-defect diŒusion in hcp metals

Crystalline materials exposed to irradiation by high-energy particles produce defects such as lattice vacancies and interstitials. If the migration properties of the vacancy and interstitial are di erent, their annihilation behaviours at di erent sinks are biased. The resulting microstructure changes lead to macroscopic deformation. In hcp metals, anisotropic di usion of the point defects is an intrinsic property related to the structure of the crystal lattice. The di usional anisotropy is changed when a stress is applied to the crystal. The intrinsic anisotropy produces irradiation growth, while the stress-induced change in the di usional anisotropy causes a deformation proportional to the applied stress, and contributes to irradiation creep. Irradiation creep due to the stress-induced change of the di usion anisotropy has been investigated extensively in the cubic but not the hcp metals. In this paper, the elastodi usion tensor of point defects in hcp metals is derived and applied to calculate the creep deformation by dislocations. The possibility that hydrostatic stress causes shear creep deformation is discussed