Growth mechanism of TaC coating on carbon fibers via molten-salt-assisted carbothermal reduction method

Reactive melt infiltration (RMI) is considered suitable process to prepare C/SiC composites with low porosity and near-net shape. However, because of inevitable reactions between molten metal and carbon fibers, mechanical properties of C/SiC composites may be affected. In this work, continuous TaC coating was successfully prepared on the surface of carbon fibers using molten salt method. Effects of temperature and holding time on microstructure, bonding configurations, and crystal structure of TaC coating were systematically investigated. With increase in temperature and time, TaC grains grew larger and TaC coating became thicker, with growth rate constant of about 3.05 × 10⁻¹⁷ m²/s. TaC coating prepared at 1200 °C for 60 min was continuous, uniform and well bonded with carbon fibers, and the main growth direction of TaC grains was [111]. Activation energy for formation of TaC coating was 295.48 kJ/mol. From a dynamic perspective, diffusion behavior of Ta ions through reaction interface was controlling step for formation of continuous TaC coating.