Processing and characterisation of cermet/hardmetal laminates with strong interfaces

• Cermets/hardmetal laminates as potential candidates for high-speed machining.
• Strong interfaces between cermet and hardmetal adjacent layers.
• Migration of molten binder during sintering.
• Compressive and tensile stresses in the hardmetal and cermet layers, respectively.
• Combined effect of toughness and compressive stresses on crack shielding.

Cemented carbides and cermets are potential materials for high speed machining tools. However, cemented carbides are not chemically stable at high temperature and cermets present poor fracture toughness. Novel cermet/hardmetal multilayer systems show a huge potential for this intended application. It would be possible to achieve the right balance of the required thermomechanical properties using cermet as temperature protective outer layers and hardmetal as reinforcement layers. In this work, preliminary results on the microstructural and mechanical characterisation of a multilayer TiCxN1−x–Co/WC–Co composite densified by hot pressing are presented, with special attention to the properties of the interface. Microstructural observations revealed the existence of strong bonding interfaces between cermet and hardmetal layers due to chemical interaction during the sintering process. As a consequence, owing to the different coefficient of thermal expansion between cermet and hardmetal, a tensile and compressive biaxial residual stress of σres,Cermet ≈ +260 ± 50 MPa and σres,WC–Co ≈ −350 ± 70 MPa was estimated in the corresponding layers. Microindentation cracks introduced in the cermet layers (the less toughness material) and propagated transversely to the layers were arrested at the interface, showing the combined effect of toughness and compressive stresses on crack shielding.