Laser surface-melting of metals studied by PAC

Abstract

High purity Pt, Ni, Cu, Fe and Al metal foils were electroplated with carrier-free¹¹¹In probe atoms and melted at 293 K using 32 ns ruby laser pulses with energy densities in the range 1–10 J cm⁻². Three distinct lattice locations of the probe atoms were detected in the melted surface layers using perturbed γ-γ angular correlation spectroscopy: (i) defect-free substitutional sites, (ii) non-unique sites with broad distributions of quadrupole interactions, and (iii) a probemonovacancy complex (for Pt only). The defect-free fraction was found to approach 100% when Pt is irradiated at 9 J cm⁻². The fraction of probes on defect-free sites was found to increase with the energy density of the pulse and with the solubility of In in the metals. The data are consistent with the idea that laser surface-melting produces high concentrations of vacancies and lattice sinks, although no thermal trapping of point defects was detected.