Effect of Different Heat Treatments on the Microstructural Evolution and Mechanical Properties of Ni-Cr-Si Alloy Fabricated by Laser Additive Manufacturing

Abstract

Ni-Cr-Si alloy samples were fabricated on mild steel via laser additive manufacturing technology. The microstructural evolution and mechanical properties of the samples were studied systematically in as-deposited conditions and under three different types of heat-treated conditions. The scanning electron microscopy, energy-dispersive x-ray spectroscopy and x-ray diffraction results showed that the structures of the as-deposited samples were mainly dendritic matrices of γ(Ni, Fe), continuous interdendritic eutectics of γ + Ni3B and discrete Cr-rich carbides and borides. After solid solution treatment, carbides (Cr7C3) and borides (CrB) precipitated on the boundary of the eutectic structure, distributing discretely in the matrix. In the solution plus aging heat-treated conditions, the interdendritic eutectics formed Ni3Fe intermetallic compounds with a layered distribution. After annealing, the grains were refined, and the hard phases (CrB) were uniformly dispersed along the grain boundary. Among the tested samples, the as-deposited specimens exhibited the highest microhardness and good wear ability at room temperature; however, the wear resistance of the as-deposited sample obviously decreased at 250 °C. The mechanical properties of the specimens were not greatly improved by solution treatment or solution plus aging treatment. The sample subjected to annealing treatment exhibited excellent wear resistance both at room temperature and at a service temperature of 250 °C.