Thermal stability and growth kinetics of the interfacial TiC layer in the Ti alloy/carbon steel system

The thermal stability and growth kinetics of the titanium carbide interfacial layer, formed in the course of the diffusion bonding of low-alloy carbon steel (0.3 wt.% C) and Ti alloy, were investigated. Thermal stability of the titanium carbide interfacial layer was evaluated based on the thermodynamic analysis of the Fe-Ti-C ternary system. Thermodynamic analysis of the Fe-Ti-C system confirmed that the titanium carbide layer is stable in contact with the steel part of the diffusion couple. An experiment with inert markers at the interface confirms that growth kinetics of the TiC layer is governed by carbon diffusion from steel to titanium alloy through the titanium carbide phase. In the 800-950 °C temperature range, carbon diffusion in austenite was found to be a rate-determining step of the titanium carbide layer growth during the initial stage of the interaction (<40 min). For advanced stages, the thickness of the layer depends on two simultaneously occurring processes, namely flow of carbon atoms through the titanium carbide layer and that from the titanium carbide layer into the titanium alloy. The estimated values of the carbon diffusion coefficient and the activation energy of the process reflect the grain boundary mechanism of carbon diffusion through the interfacial layer.