Microstructural characteristics and formation mechanism of direct laser-sintered Cu-based alloys reinforced with Ni particles

Direct metal laser sintering (DMLS) was used to consolidate Cu-based alloy powder (Cu–10Sn and Cu–8.4P) reinforced with Ni particles. Phases, microstructures, compositions, and mechanical properties of laser-sintered part were studied. It showed that particle bonding was through a liquid phase sintering mechanism involving the complete melting of matrix alloy powder and the non-melting of cores of Ni reinforcing particles. A significant smoothening of Ni particles occurred in the liquid and the dissolved Ni element alloyed with Cu element to form CuNi solid solution, leading to a coherent particle/matrix interface after solidification. The dendrites of matrix alloys developed directionally and the primary dendritic spacing was highly refined to ∼1.5 μm, due to laser-induced super high temperature gradient and solidification rate. The additive P element acted as a localized deoxidizer to prevent the sintering system from oxidation by formation of CuPO3, thereby enhancing liquid–solid wettability and resultant sintering activity. A high densification level of 95.2% theoretical density was obtained after sintering. The fracture surface of laser-sintered part was mainly featured by a strong ductile type of fracture. The dynamic nanohardness of Ni reinforcing phase and Cu-based matrix alloys reached 1.82 GPa and 0.99–1.35 GPa, respectively.