Application of discharge plasma sintering (SPS)

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Spark Plasma Sintering (SPS) is a process by which metal and ceramic powders are loaded into a mold and applied by upper and lower die presses and electrified electrodes to the Sintering powder. The powder is activated by discharge, deformed by thermoplastic and cooled. It is a powder metallurgy sintering technology for making high performance materials.

The discharge plasma sintering system can realize the pressure in the sintering process. The plasma generated by pulse current and the pressure in the sintering process are beneficial to reduce the sintering temperature of the powder. It has the characteristics of fast heating rate, short sintering time, controllable structure, energy saving and environmental protection.

Application of SPS in material preparation
Due to its unique sintering mechanism, SPS technology has the characteristics of fast heating rate, low sintering temperature, short sintering time, energy saving and environmental protection, etc. SPS technology has been widely used in the preparation of nanomaterials, functional gradient materials, metal materials, magnetic materials, composite materials, ceramics and other materials.

Nanomaterials
The traditional hot pressing sintering, hot isostatic pressing and other methods to prepare nanomaterials are difficult to ensure the nanometer size of grain, and meet the requirements of complete density. SPS technology can restrain grain coarsening obviously because of its rapid heating and short synthesis time. SPS technology can restrain grain coarsening obviously because of its rapid heating and short synthesis time. SPS can quickly cool this feature is used to control the reaction mechanism of sintering process, and avoid some unnecessary reaction, defects and the structure of the powder could be preserved in the block after sintering material, in a broader sense, it is advantageous to the synthesis of dielectric materials, especially for the preparation of nanometer materials.

Functionally gradient material
Functional gradient material (FGM) is a kind of composite material with gradient distribution in a certain direction. The sintering temperature of each layer is different, so it is difficult to be fired in one sintering by traditional sintering method. Using CVD,PVD and other methods to prepare gradient materials, the cost is very high, and it is difficult to achieve industrial production. This difficulty can be overcome by SPS technology.

SPS can manufacture ceramic/metal, polymer/metal and other materials with heat gradient, wear gradient, hardness gradient, conductivity gradient, porosity gradient, etc. The gradient layer can be up to 10 layers to realize the gradient distribution of sintering temperature.

High density, fine grain ceramics and cermets
During the SPS process, each powder particle in the sample and the interstitial space between them may themselves be a source of heat. The heat transfer process necessary for sintering by the usual method is negligible in the SPS process. Therefore, the sintering time can be greatly shortened, and the sintering temperature is also significantly reduced. For the preparation of high density, fine grain ceramics, SPS is a very advantageous sintering means.

Magnetic materials
Sintering NdFeB magnetic alloy with SPS, if sintered at a higher temperature, can get a high density, but too high sintering temperature will appear α phase and grain growth, magnetic deterioration. If sintered at a lower temperature, the powder can not be completely compacted, although it retains good magnetic properties. SPS process has the advantages of low sintering temperature and short holding time. Although the thin strips of soft magnetic alloy prepared by rapid solidification method have reached the fine grain structure of tens of nanometers, they are difficult to be prepared into alloy blocks, and their application is greatly limited. However, the magnetic properties of bulk magnetic alloy prepared by SPS can reach the soft magnetic properties of amorphous and nanocrystalline tissue strips.

Amorphous materials
In the preparation of amorphous alloy, metal mould casting method and water quenching method is often used to obtain the high cooling rate, thus obtaining amorphous organization, after adopting extrusion at a temperature below that at which crystallization temperature, rolling temperature, curing and isostatic pressing sintering method for preparation of bulk amorphous alloy, but there are many problems, such as long time heating process will make the grain growth amorphous organization, This can degrade performance. SPS is expected to make progress in this regard. According to the current research, the heating curing behavior of SPS occurs before crystallization in the process of sintering, that is, in this process, the solidification rate of the alloy is ahead of crystallization.

Conclusion
Sink plasma sintering (SPS) is a low temperature, short time fast sintering method, which plays an important role in the preparation and research of new materials. In order to meet future research and development needs, SPS equipment needs to add more functionality and pulse current capacity, etc., in order to meet larger product demand and production applications, especially the fully automated SPS production system to meet the production needs of complex shapes, high performance products and 3D functional gradient materials. It is also necessary to develop new mold materials with higher strength and better reuse rate than the graphite mold currently used, in order to improve the bearing capacity of the mold and reduce costs. In the process, the relationship between the mold temperature and the actual temperature of the workpiece is needed to better control the quality of the product.

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Spark Plasma Sintering Furnace