Laser Powder Bed Fusion Processing of High Copper Content Alloys

Abstract

In this work, the primary objective was to investigate the laser powder bed fusion (LPBF) processing of copper containing alloys and their subsequent microstructure and mechanical properties. The implementation of copper alloys into LPBF has lagged behind other alloy families, due to their intrinsic properties that are incompatible with laser processing. However, through alloying additions and the careful selection of process parameters, functional components can be produced. This work establishes the process parameter windows and the underlying mechanisms behind porosity formation for two copper containing alloys - Cu-Cr-Zr (UNS C18150) and Monel 400 (UNS N04400). The statistical design of experiments methodology devised to determine the process window was transferrable between the two alloys, proving its utility. For both alloys, densities near full theoretical were obtained, at ~98% for Cu-Cr-Zr and >99.5% for Monel 400. The LPBF produced alloys were examined through various microscopy techniques, which revealed how the rapid solidification and directional heat input of LPBF altered the microstructure compared to traditional manufacturing methods. The mechanical behaviour of the LPBF components was also investigated along with the heat treatment required to obtain desirable properties for each alloy, which differed from the traditionally produced counterparts. Mechanical properties comparable to wrought were achieved by direct ageing of LPBF Cu-Cr-Zr. In the case of Monel 400, heat treatments for homogenization were developed to mitigate and examine the effects of the segregation imparted by LPBF. The mechanical properties of these conditions differed, with the as-built and stress relieved showing high strength and ductility while the solutionized samples showed additional ductility, suggesting that the extent of segregation affected the mechanical behaviour. The tensile properties of LPBF produced Monel 400 exceeded that of the cast counterpart, while the as-built and stress relieved conditions were comparable to cold worked and stress relieved wrought.