Effect of Build Geometry and Porosity in Additively Manufactured CuCrZr

Abstract

The current work presents an understanding of microstructure and mechanical properties as a function of build geometry and build orientation in Cu-Cr-Zr via the laser powder bed fusion (LPBF) technique. Porosity, microstructure, and mechanical properties have been compared in the as-printed (AP) and heat treated (HT) LPBF Cu-Cr-Zr, between cylindrical and cube geometries, along the longitudinal (L) and transverse (T) build orientations. Varying porosity levels were observed that yielded parts with 96–97% relative density in the AP condition. The AP microstructure, characterized by a combination of optical and electron microscopic techniques, demonstrated a hierarchical microstructure, comprising of grains (2.5–100 μm) with a cellular substructure (400–850 nm) and intracellular nanoscale (20–60 nm) precipitates enriched in Cu and Zr. Unlike most materials in the AP condition, crystallographic texture was found to be absent; however, very distinct river like patterns highlighted a novel characteristic of the LPBF Cu-Cr-Zr. Upon solutionizing and aging, Cr precipitates were seen heterogeneously nucleating along cell boundaries (0.5–1.3 μm), causing up to 45% enhancement in the strength and a 4–5% lower ductility. The yield strength along the transverse orientation was 10–16% higher than that of longitudinal orientation, in both the AP and HT conditions. Fracture surface of the tensile samples exhibited micro-voids and cleavage facets and unmelted particles. In spite of the observed defects, the overall mechanical properties matched well with those obtained in nearly dense (> 99%) samples and the mechanical property debit was less than 10%.