Since the last 30 years, the cemented carbides WC–Co are processed from finer and finer powders. Both densification behaviour and microstructure evolution along the liquid-phase sintering (LPS) are different for materials prepared from powders of micronic or submicronic size. The typical features induced by the use of submicronic particles – large contribution of the solid-state densification, abnormal growth – are presented. The major questions, related to the understanding of densification hindrance and grain growth inhibition, are listed.

Sintering features of cemented carbides WC–Co processed from fine powders

Silicon carbide (SiC) porous substrates are prepared by pressureless sintering of SiC powders under an inert atmosphere of argon. The porous SiC substrates were characterized by measuring their porosity, pore size distribution, surface characteristics, and structure. Their transport characteristics were investigated using N2 and He as the test gases. Three different starting powders and four different sintering aids, Al2O3, B4C, carbon black, and phenolic resin, either by themselves or in combination, were investigated in terms of their ability to prepare good quality substrates. It was found that the porosity, pore size distribution, and transport characteristics of the resulting SiC-sintered bodies depend on the nature of the original powder, the particle size in the green SiC samples, and the type and molar ratio of the sintering aid utilized. Depending on the preparation technique, both mesoporous and macroporous materials could be prepared. These supports are currently utilized for the preparation of...

Porous Silicon Carbide Sintered Substrates for High-Temperature Membranes

This paper presents a phenomenological approach to describe the densification kinetics of tungsten carbide–cobalt powder compacts during sintering. A special sintering test including short isothermal sequences is proposed. From the results of this test a simple equation expressing the densification rate as function of temperature, relative density and green density is identified. The predictive capacity of this equation is then demonstrated by investigating the densification of the material during other sintering tests with various heating rates and with compacts of several green densities.

Phenomenological analysis of densification kinetics during sintering : application to WC-Co mixture

The microstructure of WC-Co composites sintered with VC or with a mixture of VC and Cr3C2 is investigated by several techniques in order to understand the grain growth inhibition process. In this work, using the high-resolution transmission electron microscopy and high-resolution energy-filtering electron microscopy, we are able to study on the atomic scale the microstructure and composition of the phases present in the alloys. A thin (VW)C x layer less than 1 nm thick covering all surfaces of WC grains and thin (VW)C x platelets embedded in the WC grains are evidenced. Microsteps are observed at the interface between Co and WC along the ⟨11amp;2macr;0⟩WC directions. Small (VW)C x precipitates lie on the (0001)WC and {10amp;1macr;0} facets of these steps. On the (0001) surface of WC grains, other stacking sequences of the metal planes are sometimes observed and, in particular, the occurrence of the compound (VW)2C is shown. Owing to these observations a grain growth inhibition mechanism is proposed.

Structure and role of the interfacial layers in VC-rich WC-Co cermets

The sintering of cemented carbides based on WC–Co with different carbon contents and additions of (Ti,W)C has been studied by dilatometry and analysed in terms of a densification model. Shrinkage starts around 1000 °C for WC–Co and in the range 1100–1250 °C for WC–(Ti,W)C–Co. Although a high carbon content initially delays shrinkage in WC–Co it leads eventually to high shrinkage rates and a fully dense material in the shortest time. Practically no difference was found between low and medium carbon contents. For WC–(Ti,W)C–Co, onset of shrinkage depends more strongly on composition and increases with decreasing carbon content. Shrinkage rates are described with a proposed model based on uniaxial viscosity, viscous equivalent of Poisson’s ratio and sintering stress. The three densification stages observed for WC–Co materials reduce to two stages for WC–(Ti,C)C–Co, where higher apparent activation energies also are observed during solid state sintering.

Sintering shrinkage of WC-Co and WC-(Ti,W)C-Co materials with different carbon contents

A general morphological approach of sintering kinetics: application to WC–Co solid phase sintering

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A general morphological approach of sintering kinetics: application to WC–Co solid phase sintering