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

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 A degrees 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 A degrees C, however, they were not observed after 1.2 strain at 1075 A degrees C. The dislocation generation rate during deformation at 1075 A degrees 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 A degrees 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 A degrees C resulted in strain-induced precipitation in all alloys and < 20 nm particle growth in the high and middle Nb+C alloys.