Discharge plasma sintering (SPS) of cermet composites

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Discharge plasma sintering (SPS) of cermet composites

Discharge Plasma Sintering, Spark Plasma Sintering), SPS is the metal and ceramic powder into the mold, using upper and lower die and the electricity will be specific on Sintering powder Sintering power and thrust pressure, after discharge, activation, thermal plastic deformation and cooling and complete, is a kind of preparing high-performance materials of powder metallurgy Sintering technology.

SPS mainly USES an electric field formed by an applied strong pulse current to clean the oxide and adsorbed gas on the surface of powder particles, purify the material, activate the powder surface, improve the diffusion ability of the powder surface, and then use a strong current to short-time heat the powder under low mechanical pressure for sintering densification. The energy consumption is only 1/5~1/3 that of the traditional sintering process.

Therefore, SPS technology has incomparable advantages over hot-pressing and hot-isostatic pressing technologies:

(1)Low sintering temperature (200~300℃ lower than HP and HIP), short sintering time (only 3~10min, while HP and HIP need 120~300min), low energy consumption per piece;
(2) Special sintering mechanism, giving the material new structure and performance;
(3)The sintered body has high density and fine grain, which is a kind of near-net forming technology;
(4) the operation is simple, unlike the hot isostatic pressure, the need for very skilled operators and special mold technology.

Cermet composite material
Metal – ceramic composite materials with a single metal or ceramic materials incomparable superior performance, the material, which can not only retain the advantages of the original component parts and produce what the original component does not have new performance, according to the actual need of engineering, design of materials with special performance, group is interface between RMB or yuan composition gradient change. There are mainly carbide fund ceramic and oxide fund ceramic.

When carbide foundation ceramics are prepared by conventional sintering method, the general sintering temperature is around 1500℃, the maximum temperature holding time is above 0.5h, and the time required for sintering density is about 10h. Moreover, it is difficult to prepare nano-sized cermet materials by conventional sintering methods. At the same time, the sintering temperature of partial oxide fund ceramics is too high, so it is difficult to sintering density by conventional sintering method. As the general mixing method of cermet is ball grinding mixing, this mixing method is easy to oxidize the initial powder and bring in other impurities, thus reducing the interface wettability of the metal and ceramics and ultimately affecting the performance of the sintered material. SPS can purify and activate the initial powder, and cermets can be used for sintering. At present, the cermet materials successfully prepared with SPS include WC-CO, TiC-Ni, Cr2O3-W.

Wc-co is the most widely used cermet material at present, and also the most studied material using SPS technology. Traditional cemented carbide sintering is carried out in a protective atmosphere furnace and a vacuum furnace by heating the liquid phase above the temperature. In order to prevent grain growth during sintering, a small amount of grain growth inhibitor is generally added to the ingredients, which makes the process complicated and may reduce the strength of the product. Only micron-sized (> 1 m) materials can be prepared. Cha S I et al. conducted SPS sintering study on micron-sized WC-CO composite powder, and found that under the sintering temperature of 1050℃, pressure of 50MPa and heat preservation for 10min, the material could be sintered into densification, and the grain size was small and the hardness was higher than that of the same powder sintered under the conventional sintering condition.

Cermet application
Aerospace field
In the field of aerospace, high temperature resistance, wear resistance, high strength, high stability and other harsh environmental and technical requirements, cermet has a broad space to play. Cermet has good wear resistance and high temperature strength. It can be used to manufacture valves and stationary rings for aerospace engines.

Ship field
In general, the coating of metal alloy material on the surface of ship is easy to fall off due to friction, potential corrosion and sea water corrosion, thus losing the function of the coating. In addition to the toughness of the metal, ceramic coating has the chemical inertness of the ceramic itself, which can effectively prevent the corrosion caused by sea water and potential.

Manufacturing and processing
High hardness, good wear resistance, high bending strength, good toughness, oxidation resistance and other properties determine that cermets play an irreplaceable role in the field of manufacturing and processing, especially in measuring tools and cutting tools, compared with cemented carbide, cermets have obvious advantages.