Cold Sprayed Deposits Characterized by Positron Annihilation Spectroscopy

Abstract

Cold spray (CS) is a rapid additive manufacturing method for deposition of metallic materials at rates significantly exceeding the laser-based methods, while retaining high deposit quality and low process cost. The mechanisms of the high-rate, extensive deformation of the materials in the CS process were recently intensively studied on macro- and meso-levels. In this paper, we introduce positron annihilation spectroscopy as a viable and reliable analytical method to study lattice defects created in the cold sprayed materials on the atomic-scale level. For the first demonstration, four different base metals were selected (Al, Cu, Ni, and Ti). A high density of dislocations was observed in all four deposits. In addition, deposits of fcc metals (Al, Cu, and Ni) also contain a considerable concentration of vacancy clusters. The results show that the extremely fast deformation in cold spray deposition process prevents recovery of vacancies which tend to agglomerate into clusters.