High-Pressure Nitrogen Modified Functional Gradient Hardmetals: Preparation, Characterisation and Cutting-Performance

摘要

In the present work nitrogen pressures of 5 and 25bar were used for a diffusional treatment to modify the surface and near-surface areas of (Ti,W)(C,N)/Co-based alloys to develop functional gradient hardmetals (FGHMs). This was performed by a post-treatment at T=1200°C of already dense sintered compacts. Upon this treatment Ti(C,N) diffusion layers at the surface formed in materials with a high overall Ti(C,N) content in the starting formulation. Within the diffusion layers it was found that the [N]/[C] ratio decreases towards the interior. From systematic experiments a parabolic layer growth rate for these layers could be identified, the thickness of which is also dependent on the nitrogen pressure, i.e. the growth rate is higher the higher the N2 pressure. Various cutting tests were carried out under conditions suited to compare the FGHMs with conventional hardmetals and to find out the optimum layer thickness. A substantial better performance was obtained for the described FGHM type.