Enhanced hardness and moderate thermal conductivity of Cu-2.4Ni-0.7Si alloy processed via selective laser melting followed by suitable heat treatment

The crystallographic texture, thermal conductivity, and microhardness of the Cu-2.4Ni-0.7Si alloy processed by selective laser melting (SLM) were investigated. The SLM sample shows columnar grains with stronger (100) preferred orientation, and the content of high-angle grain boundaries (HAGBs) is 64.6%. It owns the lower microhardness of 89.73 Hv and the higher thermal conductivity of 187.83 W/m K. After heat treatment for 12 and 25 h, the microstructure of the samples changes from the coarser columnar grains to the smaller equiaxedlike grains with the HAGBs of 59.6% and 61.8%, which show (100), (101), and (111) orientations equally then exhibit stronger (101) and (111) preferred orientation. Moreover, the precipitates vary from Ni3Si with a size of 0.5 mu m to Ni2Si with a size of 1 mu m, hence resulting in higher microhardness of 180.02 and 170.03 Hv. Due to the precipitates, lower texture index and HAGBs' content that generate the more grain boundary scattering for electron and phonon transport lead to lower thermal conductivity of 161.57 and 177.83 W/m K. This study suggests that thermal conductivity and microhardness of the SLM Cu-Ni-Si alloy can be tailored by controlling suitable heat treatment condition.