Non-equilibrium thermodynamics of plasma-nitriding of tantalum

The thermodynamic aspects involved in plasma-nitriding of tantalum were discussed. The effects of plasma on surface morphology, roughness, hardness depth profile, phase structure and composition of nitriding layer of tantalum were experimentally determined. The concept of super-equilibrium hydrogen and theory of reaction-coupling in non-equilibrium conditions were introduced into the calculation of surface reactions during plasma-nitriding of tantalum and used to explain theoretically the effects of hydrogen and plasma on the process of nitriding of tantalum at low temperature as compared with high melting point of tantalum. According to the non-equilibrium calculation, the partial non-equilibrium diagram of Ta-N-O under the conditions of nitriding was given which is in good agreement with the experimental results.