Defect production by near-surface displacement cascades in alpha-Zr

Computer simulations have shown that a nearby surface can engender a signif icant increase in the number of vacancy defects produced by high-energy dis placement cascades in metals of cubic crystal structure. In the present wor k, the influence of a surface on the production of lattice defects in the b ulk by displacement cascades of up to 10 keV in energy in alpha-Zr has been studied. The basal- or prism-plane surfaces were considered, with the dire ction of the primary recoil atom making either a high or a low angle to the surface normal. This hcp metal is of interest because self-interstitials m igrate preferentially along the basal planes, and so the crystallographic o rientation of the surface can influence the final defect state of cascade d amage. Surface and subsurface damage increases with increasing energy. The surface damage is much larger for the prism-plane surface. Whereas stable i nterstitial defects are more readily generated below a basal-plane surface, they are deposited at greater depth below a prism-plane surface. The produ ction of vacancies and interstitials below the surface is contrasted with d ata for simulations of cascades in the bulk. The results are interpreted in terms of defect properties in Zr and compared with those for cubic metals.