Metallurgy and thermochemistry of cermet/hardmetal laminates

• Composition, doping and nitrogen pressure influence the sintering, liquid-phase formation, outgasing and microstructure of cermets and cermet/hardmetal mixtures.
• Cermets and hardmetals (cemented carbides) can be combined to layered structures (laminates).
• Interfaces in cermet/hardmetal laminates depend on composition and nitrogen pressure upon sintering.
• Laminates have great potential of reduced W consumption for cutting tools.

Laminates of Ti(C,N)–WC–(Ta,Nb)C–Co/Ni cermets with WC–Co hardmetals were studied with respect to liquid-phase formation, bulk microstructure and microstructure evolution at the various interfaces. To adapt the cermet to the sintering behaviour of the hardmetal, investigations on mass change, influence of nitrogen pressure, as well as Cr and C doping on liquid-phase formation temperatures were performed. In addition, shrinkage and CO and N2 outgasing were studied.The bonding of cermets (CMs) to hardmetals (HMs) and that of 1:1, 1:2 and 2:1 mixtures of cermet/hardmetal (CM/HM) is tight, i.e. no pores occur. No major distortion or bending was observed although the shrinkage of each of the alloys was quite different. At the interfaces an intermixing occurred because of diffusion. At the CM/HM 2:1/1:2 interface a graded diffusion zone with more than 100 μm thickness formed.In a bi-layer cermet/hardmetal laminate the interface microstructure was dependent on the nitrogen pressure in the sintering chamber. Enrichment of Co and nitrides occurred at lower than equilibrium pressure, whereas WC precipitated in the cermet at high nitrogen pressure.

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