The role of molybdenum in the hard-phase grains of (Ti, Mo)(C, N)–Co cermets

Abstract

The evolution of the core–rim interface in Ti(C, N)-based cermets containing Mo is studied by scanning electron microscopy and conventional and high-resolution transmission electron microscopy as a function of the annealing temperature. A heavily disordered zone on the nanometric scale is observed close to the interface with the core of Ti(C, N) grains in as-sintered samples. It reorders after annealing at a high temperature. This disorder is correlated with the presence of Mo in the rim during sintering, which enhances the strength of the core–rim interface as a barrier for the diffusion of atoms from the core. It avoids the complete dissolution of small Ti(C, N) grains from the original powder and limits the grain growth. It also acts as a barrier against dislocation movements during plastic deformation. This effect, as well as the small final grain size determined by the presence of Mo, contributes to the good mechanical properties of Mo-containing cermets at intermediate temperatures.

Acknowledgements

The present authors thank Professor W. Benoit, Dr G. Feusier, Dr T. Viatte and Dr D. Caillard for fruitful discussions. They express their gratitude to Stellram-Gland, Switzerland, for providing samples, and Centre Interdépartemental de Microscopie Electronique, Ecole Polytechnique Fédérale de Lausanne for TEM and SEM facilities. The financial support from the Swiss Commission pour la Technologie et l’Innovation (project 32105.1) is gratefully acknowledged.