Effect of solidification conditions on microstructure and mechanical properties of γ-Ni/Mo₂Ni₃Si alloy

γ-Ni toughened Mo₂Ni₃Si ternary metal silicide alloy was designed and fabricated by the laser melting deposition process. Differential scanning calorimetry (DSC) and high-temperature microscopic analysis indicated that the Mo₂Ni₃Si alloy has an eutectic temperature of 1287°C and a liquidus temperature of 1355°C. In this paper, the solidification microstructures of γ/Mo₂Ni₃Si alloy under furnace cooling, water cooling and laser surface remelting conditions were studied. Results showed that under furnace cooling and water cooling conditions, the volume fraction of Mo₂ Ni₃ Si primary dendrite and the secondary dendrite arm spacing decreased with increasing cooling rate. However, for the alloy under laser surface remelting condition which had the highest cooling rate (-10³ K/s), the volume fraction of Mo₂Ni₃Si primary dendrite increased markedly to about 62%. Due to its finest structure, the laser surface remelted γ/Mo₂Ni₃Si alloy possessed the optimum mechanical property (600HV), while many microcracks were observed on the Mo₂Ni₃Si primary dendrite for the furnace cooled γ/Mo₂Ni₃Si alloy and its coarse dual-phase structure was much unfavourable to mechanical property.