Microstructure and performance of functionally graded Ti(C,N)-based cermets prepared by double-glow plasma carburization

Ti(C,N)-based cermets were subject to double-glow plasma carburization which substantially improved the surface hardness. The microstructures were studied using scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDX). It was found that the double-glow plasma carburization introduced a graded surface zone enriched in carbonitride phase and deficient in binder phase. The microstructure of the surface zone of the carburized cermet was different from that of the as-sintered cermets. Besides the carbonitride grains with typical core-rim structure, the amount of smaller grains without obvious rim phase increased greatly, and some carbonitride grains adjoined and congregated with each other. The formation of the graded layer was due to the high carbon activity in the surface region during carburization, which caused the titanium, molybdenum and tungsten to transport outwards and forced the nickel to transfer inwards. After double-glow plasma carburization, the surface hardness was increased greatly and the hardness distribution along the depth was in accord with the binder distribution.