Ta-C micro-composite material formed by heat treatment of plasma carburized layer

Tantalum-carbon micro-composite material (MCM) was produced by a process which combines plasma carburizing and heat treatment. The fabrication was performed in inductively coupled radio-frequency plasma, using CH ₄-H₂-Ar mixtures, followed by a two-step heat treatment which includes solid solution and aging. The crystallography, microstructure and composition of the intermediate layers and of the MCMs were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive analysis and atomic force microscopy. The mechanical properties of the layers and of the MCMs were studied by laterally resolved depth-sensing indentation. It was found that the size and hardness within the recrystallized grains and carbon-rich grain boundaries are strongly related to the composition and thickness of the initial carburized layer. The mechanisms involved in the different process steps, in particular redistribution of Ta-C compounds and carbon diffusion towards the film bulk, are discussed.