Growth kinetics and mechanical properties of the V2C and V8C7 carbide layers on iron substrate

To explore the formation of vanadium carbide layers (V2C and V8C7) on the surface of an iron-based alloy produced by a diffusion-controlled in situ reaction in the solid state from 950 °C to 1050 °C, the growth kinetics of the V2C and V8C7 layers were evaluated based on the diffusion. The experimental results reveal that the growth of vanadium carbide layers is controlled by carbon diffusion from the iron substrate to the thin vanadium plate, where the growth kinetics of the V2C and V8C7 layers exhibit a parabolic growth law. Simultaneously, it is also accompanied by vanadium and iron diffusion. The results for the obtained diffusion coefficient and the growth activation energy indicate that the diffusion mechanism of carbon in the V2C layer and V8C7 layer is predominantly grain boundary diffusion and that the formation of the V8C7 layer needs to overcome a higher energy barrier than that of the V2C layer. Additionally, the precipitated phase σ-FeV is found to be located at grain boundaries of the V8C7 layer. Investigations into the mechanical properties by indentation technology show that the hardness and Young's modulus of the V8C7 layer are slightly greater than those of the V2C layer. The fraction toughness of the dominant V8C7 layer with values from 0.88 to 4.34 MPa·m½ decreases with the increasing load. The precipitated phase σ-FeV exhibits an effect on the hardness and fraction toughness. The obtained double vanadium carbide layers improve the mechanical performance of the surface of the iron-based alloy.