Effect of the nitrogen multi-sources on the microstructure and hardness of the graded surface layer in WC–Co–Cubic cemented carbides.

Nitrogen plays a key role in tailoring the surface structures in WC–Co–Cubic graded cemented carbides. In this study, graded cemented carbides were sintered at 1450 °C for 2 h in a N-free atmosphere using TiN, ZrN, and HfN as multiple N sources. The elemental and compositional distributions of the resultant cemented carbides were measured to determine the microstructural evolution in the graded surface layer. For alloys incorporated with different N sources, two key characteristics, the residual cubic phase and thickness of the graded layer, were investigated. It was revealed that the thermodynamic formation energies of the cubic nitrides was the main factor to the microstructural evolution. In addition, the hardness distributions in the graded layers were measured using micro-indentation tests. Overall, a relationship between microstructure and hardness was established from the surface to the core of the investigated materials. [ABSTRACT FROM AUTHOR]