Tungsten carbide liquid phase sintering

Corresponding Co compounds may form during liquid-phase sintering of cemented carbides if the carbon balance is low analogous Fe compounds (containing also Mo, V, and Cr) occur in tungsten alloyed steel. 

Due to the tailored properties of liquid phase sintered silicon carbide (LPSSiC) it is used as dewatering elements in the paper machinery and as rings for highly stressed gas seals. It is a price competitive alternative to silicon nitride materials and outperforms alumina and tungsten carbide materials. In addition, LPSSiC is proposed as neutral matrix in ceramic matrix composites containing plutonium to burn the world s stockpiles of military plutonium in thermal or fast reactors [278]. 

Other innovators include brothers Pierre and Jacques Curie, French physicists who discovered piezoelectricity around 1880 French chemist Henri Moissan, who combined silicon carbide with tungsten carbide around the same time as Acheson and German mathematician Karl Schroter, who in 1923 developed a liquid-phase sintering method to bond cobalt with the tungsten-carbide particles created by Moissan. 

Mixtures of powders of two materials sinter very rapidly if one of them melts at the sintering temperature. Initially capillary action causes the liquid phase to rapidly wet the solid phase, causing an initial contraction. Then as the solid phase dissolves in the liquid it is rapidly transported to locations that decrease the pore volume. Carbide tool material is made from a mixture of cobalt and tungsten carbide powders sintered below the melting point of cobalt. The volume fraction liquid must be limited so capillarity can retain the shape during sintering. 

The most important property of tungsten carbide in its utilization in cemented carbides is its ability to dissolve partially in compressed powder mixtures of WC and ferrous metals, particularly cobalt, at 1300 to 1500°C. In the case of sintering with a liquid phase, WC partly crystallizes out of the binder phase of the WC-Co-alloy upon cooling. It becomes embedded in the tough but hard (not brittle) binder phase. 

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