Laser Powder Bed Fusion of CuNi2SiCr alloy: Process parameters optimization and electro-mechanical characterization

Among metals, copper has one of the highest values of electrical and thermal conductivities, second only to silver. These properties, in addition to a good corrosion resistance and ease of both extraction from ore and fabrication, make copper a promising candidate for many applications including the use of this material for heat exchangers. Other applications are in electronics, pipes and fittings, automotive and electrical industries. The increasing ability of Additive Manufacturing (AM) technologies to process metals in past decades, has diversified this expanse of applications. AM has been applied to increase the efficiency of the already existing applications of copper like induction-coils while also creating new potential application-areas, for example, production of rocket engine nozzles. This has enhanced the performance of the products multi-fold and made the otherwise expensive technology, economically feasible. Also, copper alloys are known to have a good blend of moderate physical strength, electrical and thermal conductivities. It makes them desirable to use in harsh environments where a combination of the properties is necessary. This thesis focuses on CuNi2SiCr alloy, which exhibits high corrosion resistance, creep resistance, wear resistance and high stiffness at elevated temperatures. These properties are exploited in applications such as tooling-inserts, valves and brackets/fixtures. The absence of extensive research on this particular alloy in the field of AM, increases the need to investigate its characteristics. Test samples were manufactured from pre-alloyed powder using Laser Powder Bed Fusion (LPBF) technique equipped with a laser with wavelength in the near-infrared range. Test-samples were printed using different sets of machine process parameters (scanning speed, hatching distance and layer thickness) to find the optimal combination that yields the highest relative density. The limited power of the LPBF machine used (Concept Laser Mlab R), coupled with the high thermal conductivity and low absorption of copper leads to microstructure with residual porosity (around 3 %). Subsequently, a batch of samples were fabricated using the optimized process parameters and relative densities above 97% were obtained. To observe different aspects of the microstructure, namely grains and melt-pools, various etchants were applied to the polished-test samples. Microscopic analysis also hinted towards presence of oxides in the defects. An upward trend of relative densities was observed for samples with increasing cross-sectional areas, which can be an interesting research area for future studies.