Thermal/kinetic study of the formation mechanism of NbC-Fe composite layer on the surface of GCr15 prepared by hot pressure diffusion

Abstract

In this study, an NbC-Fe composite layer is in situ prepared on the surface of GCr15 bearing steel. The formation mechanism of the composite layer was investigated in terms of thermodynamics, dynamics, and crystal structure transformation processes during the in situ reaction. According to computational thermodynamics, the reaction at 1150 °C–1200 °C allows NbC, Fe3C, Cr3C2, Cr7C3, and Cr23C6 phases to spontaneously react and stabilize in the Fe-C-Nb-CR system. The functional relationship between the growth thickness, time, and temperature of the NbC-Fe composite layer was obtained experimentally and via computational dynamics. Particularly, the growth activation energy, Q, of the NbC-Fe composite layer was calculated to be 367.06 kJ mol−1. The combination of computational thermodynamic/kinetic research and experimental observation of crystal transformation data revealed that the formation mechanism of NbC in the NbC-Fe layer on the surface of GCr15 caused the C atoms in the bearing steel diffuse into the Nb plate and occupy the octahedral gap of the Nb unit cell to form NbC. In the formation mechanism of the NbC-Fe composite layer, C and Fe atoms partially migrated from the pearlite and diffused towards the direction of the Nb plate to form the NbC-Fe composite layer.