Effect of post-heat treatment on the thermophysical and compressive mechanical properties of Cu-Ni-Sn alloy manufactured by selective laser melting

This study investigated the effect of heat treatment on the microstructure, room- and high-temperature mechanical properties, and thermal properties of selective laser melted Cu-Ni-Sn alloy. Initial microstructural observation confirmed that the as-fabricated sample was composed of Cu, Cu6Sn5, Cu3P and undissolved Ni phases, and then the heat-treated sample was composed of Cu-Ni solid solution, (Cu, Ni)(3)Sn and (Cu, Ni)(3)P. Room- and high-temperature compression tests (25 degrees C similar to 500 degrees C) were performed, and the yield strengths at room temperature measured 230.4 MPa and 346.0 MPa for as-fabricated and heat-treated materials, which indicates an approximately 50% increase in strength after heat treatment. Furthermore, as temperature increased, a phenomenon where the yield strength inverts occurred for both materials, and the cause of such a phenomenon was identified to be due to the difference in strengthening mechanisms. Thermal diffusivity is lower in heat-treated sample at all temperatures, but on the other hand, thermal conductivity interestingly is higher in heat-treated sample than as-fabricated sample (As-fabricated sample: 30.7-44.0 W/m.K, heat-treated sample: 32.8-49.6 W/m.K). The reason for this is identified to be due to microstructure evolution and defect control after heat treatment. Correlations between initial microstructures and mechanical- and thermophysical-properties were also discussed based on these findings.