Effect of niobium content on the precipitation behavior and mechanical properties of Ni-Cr alloys

The effect of niobium content on the precipitation behavior and mechanical properties of Ni-Cr alloys, both in as-deposited and heat-treated states, was investigated. Microscopic characterization results revealed that the microstructures of the Ni-Cr alloys consisted of γ dendrites arranged in parallel along the deposition direction. The primary precipitation phase identified was MC (M=Nb, Ti), located between the dendritic crystals. In alloys with a 2.13 wt.% Nb content, Cr₂₃C₆ is discretely distributed along the grain boundaries. When the Nb content increases to 3.00 wt.%, Laves phases emerge within the grains. Mechanical analysis results indicated that the austenite grains were refined in the as-deposited alloys and the area fraction of precipitates increased from 0.68% to 0.79% with the increase in Nb content, leading to enhanced strength and hardness of the alloys. Post heat treatment promoted the formation of MC (M = Nb, Ti) precipitates, resulting in a significant increase in the area fraction of these precipitates. This led to a slight decrease in impact energy value, but a marked increase in alloy strength. The heat-treated alloys with 3.00 wt.% Nb content exhibited the highest tensile strength of 675 MPa.