Defects in Laser Surface-Melted Metals Studied by Pac

Abstract

ABSTRACTFollowing nanosecond-duration laser surface-melting, lattice locations of illIn probe atoms in Ni and Pt samples were studied using the technique of perturbed gamma-gamma angular correlations (PAC). After melting and annealing, no probe atoms were observed to become associated with unique vacancy clusters observed after other methods of damaging, while many probe atoms were found on non-unique sites. 111In probe atoms were observed to move to the surface and to be expelled at anomalously low temperatures. These observations are partially reconciled by the hypothesis that probe atoms diffusing in the molten surface layer become trapped on dislocations during resolidification, and during later annealing return to the surface via pipe diffusion.