Spark plasma sintering (SPS) is a kind of powder metallurgy sintering technology for manufacturing high-performance materials, which is to put metal, ceramic and other powder into the mold, apply specific sintering power and pressing pressure to the sintered powder by upper and lower die punching and electrifying electrode, and complete by discharge activation, thermoplastic deformation and cooling.
The plasma generated by pulse current and the pressure in the sintering process can reduce the sintering temperature of the powder. It is characterized by fast heating rate, short sintering time, controllable structure, energy saving and environmental protection.
Pulse current through powder particles
Application of SPS in material preparation
Due to the unique sintering mechanism of SPS, SPS technology has the characteristics of fast heating rate, low sintering temperature, short sintering time, energy saving and environmental protection. SPS technology has been widely used in the preparation of nano materials, functionally gradient materials, metal materials, magnetic materials, composite materials, ceramics and other materials.
It is difficult to ensure the nanometer size of grains and achieve the requirement of complete densification by traditional hot pressing sintering and hot isostatic pressing. The grain coarsening can be inhibited by SPS technology because of its rapid heating and short synthesis time. The grain coarsening can be inhibited by SPS technology because of its rapid heating and short synthesis time. SPS can be used to control the reaction course of sintering process and avoid some unnecessary reactions, which may keep the defects and substructures in the bulk materials after sintering. In a broader sense, this is conducive to the synthesis of metastable materials, especially for the preparation of nano materials.
Functionally gradient materials
Functionally 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 sintered at one time by traditional sintering method. Using CVD, PVD and other methods to prepare gradient materials, the cost is very high, and it is difficult to realize industrial production. This difficulty can be overcome by SPS technology.
SPS can be used to manufacture ceramic / metal, polymer / metal and other materials such as heat resistance gradient, wear resistance gradient, hardness gradient, conductivity gradient and porosity gradient. The gradient layer can be up to 10 layers to realize the gradient distribution of sintering temperature.
High density, fine grain ceramics and cermets
In the SPS process, each powder particle and the gap between them may be the source of heat. The necessary heat transfer process in SPS process can be neglected. Therefore, the sintering time can be greatly shortened and the sintering temperature can also be significantly reduced. SPS is an advantageous sintering method for preparing high density and fine grain ceramics.
The NdFeB magnetic alloy sintered by SPS can obtain high density if it is sintered at higher temperature. However, if the sintering temperature is too high, α phase and grain growth will occur, and the magnetic properties will deteriorate. If sintered at a lower temperature, the powder can not be fully compacted although it can maintain good magnetic properties. SPS process has the advantages of low sintering temperature and short holding time. Although the soft magnetic alloy ribbons prepared by rapid solidification method have reached tens of nanometers of fine grain structure, it is difficult to be prepared into alloy blocks, and the application is greatly limited. However, the magnetic properties of the bulk magnetic alloy prepared by SPS can reach the soft magnetic properties of amorphous and nanocrystalline ribbons.
In the preparation of amorphous alloy, the metal mold casting method and water quenching method are often used to obtain higher cooling rate, so as to obtain the amorphous structure. Then the bulk amorphous alloy is prepared by warm extrusion, warm rolling, impact curing and isostatic pressing sintering below the crystallization temperature. However, there are many problems, such as long-time heating process will make the amorphous structure produce grains Grow up, which worsens performance. SPS is expected to make progress in this aspect. The current research shows that the heating solidification behavior of SPS occurs before crystallization in the sintering process, that is, the solidification rate of the alloy is ahead of crystallization in this process.
Summary and Prospect
Spark plasma sintering (SPS) is a rapid sintering method with low temperature and short time, which plays an important role in the preparation and research of new materials. In order to meet the future research and development needs, SPS equipment needs to add more functionality and pulse current capacity, in order to meet the greater product demand and production applications, especially the fully automated SPS production system, to meet the production needs of complex shape, high-performance products and three-dimensional functionally gradient materials, and also need to develop graphite mold with higher strength and repeatability than the currently used ones In order to improve the bearing capacity of the mold and reduce the cost, we need to establish the relationship between the mold temperature and the actual temperature of the workpiece in order to better control the product quality.
SPS equipment developed and produced by Shanghai Haoyue
Haoyue technology is a high-tech enterprise integrating R & D, production and sales of electric furnace. The company has been focusing on the four fields of semiconductor materials, carbon materials, advanced ceramics and composite materials and lithium battery materials, with rich industry experience and professional technology, dedicated to serving customers and providing perfect integrated industrial solutions.