High temperature dislocation structure and NbC precipitation in three Ni–Fe–Nb–C model alloys

Abstract

In this original work, the dislocation structure and NbC precipitation were investigated in three Ni-based alloys (70Ni–Fe–0.331Nb–0.040C, 70Ni–Fe–0.851Nb–0.114C and 70Ni–Fe–1.420Nb–0.157C, wt%) thermomechanically processed in the temperature range of 1250–1075 °C. The dislocation structure inhomogeneity (dislocation networks and cell walls), which we observed in the middle and high Nb+C alloys, resulted from the dislocation pile-ups in the vicinity of >200 nm NbC particles. The dislocation density around >200 nm particles exceeded the average values by 5–7 times, and that in the cell walls might exceed the average values by 10 times. Twins and stacking faults were observed in all alloys after solution treatment at 1250 °C, however, they were not observed after 1.2 strain at 1075 °C. The dislocation generation rate during deformation at 1075 °C varied with alloy composition and increased with an increase in the <20 nm particle number density. During cooling in the temperature range of 1250–1075 °C, the majority of particles were growing in the high Nb+C alloy, the <20 nm particles were growing in the middle Nb+C alloy and all the particles were dissolving in the low Nb+C alloy. Deformation to 1.2 strain at 1075 °C resulted in strain-induced precipitation in all alloys and <20 nm particle growth in the high and middle Nb+C alloys.