SPS discharge plasma sintering furnace
SPS is the abbreviation of Spark Plasma Sintering and is used for spark plasma sintering.·
Spark plasma sintering (SPS) is a fast, low-temperature, energy-saving and environmentally friendly material preparation technology.
1. Development of spark plasma sintering furnace
With the development of high-tech industry, the variety and demand of new materials, especially new functional materials, are increasing. New functions of materials call for new preparation technology. Spark plasma sintering (SPS) is a new rapid sintering technology developed in recent years. Because SPS technology combines plasma activation, hot pressing and resistance heating, it has the advantages of fast heating, short sintering time, uniform grain size, controlling the fine structure and obtaining of sintered body. The technology utilizes pulse energy, discharge pulse pressure and instantaneous high temperature field generated by Joule heat to realize sintering process, which is of great significance for the preparation of high quality, high efficiency, low consumption and low cost materials. It has shown great superiority in the preparation of nanomaterials, composite materials and so on. It has been applied to metals, ceramics, composite materials and nano-materials. The preparation of functional materials such as rice bulk materials, amorphous bulk materials, gradient materials and so on. At present, many universities and research institutes at home and abroad use SPS to research and develop new materials, and to further study and explore its sintering mechanism and characteristics, especially its rapid heating characteristics, which can be used as an effective means to prepare nano-bulk materials, so it has attracted special attention of materials academia. The sintering mechanism of SPS is still controversial, especially the intermediate sintering process needs to be further studied.
2. Advantages of spark plasma sintering
Spark plasma sintering (SPS) can produce many favorable effects for rapid sintering because of the strong pulse current applied between powder particles. Compared with conventional sintering technology, it has the following advantages:
Improving the Microstructure and Properties of Ceramics
Spark plasma sintering combines plasma activation, hot pressing and resistance heating. It has the advantages of fast heating speed, short sintering time, low sintering temperature, uniform grain size, good control of the fine structure of sintered body and high density of materials. It also has the advantages of simple operation, high reproducibility, safety and reliability, space saving, energy saving and low cost.
3. Principle of plasma sintering technology
At present, the mechanism of SPS sintering has not reached a unified understanding, and the intermediate process of SPS sintering needs to be further studied.
At present, it is generally believed that the SPS process not only has the Joule heat of hot pressing sintering and the plastic deformation caused by compression to promote the sintering process, but also generates DC pulse voltage between powder particles, and effectively utilizes the spontaneous heating effect produced by discharging between powder particles, thus producing some special phenomena of SPS process.
The effect of applying DC switching pulse current in SPS is as follows:
Firstly, due to the discharge shock wave generated by pulse discharge and the high-speed flow of electrons and ions in the opposite direction in the electric field, the gas adsorbed by the powder can escape, and the initial oxide film on the surface of the powder can be broken down to a certain extent, so that the powder can be purified and activated.
Secondly, because the pulse occurs instantaneously, intermittently and at high frequency, the discharging heat generated in the untouched part of the powder particles and the Joule heat generated in the contact part of the powder particles greatly promote the diffusion of the atoms of the powder particles, and the diffusion coefficient is much larger than that under the normal hot pressing conditions, thus achieving the rapid sintering of the powder.
Thirdly, with the addition of ON-OFF fast pulses, the discharge parts and Joule heating parts in the powder will move rapidly, and the sintering of the powder can be homogenized. It is a characteristic of SPS process that the pulses are concentrated at the grain boundaries.
In SPS process, when the particles are discharged between them, local high temperature as high as several thousand degrees to ten thousand degrees will be produced instantaneously, evaporation and melting on the surface of the particles will occur, and neck will be formed at the contact point of the particles. As heat is transferred from the heating center to the surface of the particles and diffused around them, the neck will rapidly cool and the vapor pressure will be lower than other parts.
Evaporation-solidification transfer is another important feature of SPS process. Under the action of pulse current heating and vertical unidirectional pressure, bulk diffusion and grain boundary diffusion are strengthened, which accelerates the Sintering Densification process. Therefore, high quality sintered body can be obtained at lower temperature and shorter time. The SPS process can be regarded as the result of particle discharge, conductive heating and pressure. S. W. Wang and L. D. Chen studied the SPS sintering of conductive copper powder and non-conductive Al2O3 powder respectively. They believed that there were different sintering mechanisms between conductive and non-conductive materials. There were Joule thermal effect and pulse discharge effect in conductive powder, but the sintering of non-conductive powder was mainly due to the heat conduction of dies.
The intermediate process and phenomena of spark plasma sintering are very complex. Many scientists have established models for the sintering process of SPS. U. Anselmi-Tamburini et al. simulated the current and temperature distribution in SPS process, and considered that the temperature distribution was closely related to the current distribution.
Application of Anchor Point and Anchor Point
SPS equipment makes it possible to manufacture very special new materials, such as:
* Nano-materials can be sintered without significant grain growth.
* Composite materials
* Tungsten carbide or other hard materials
* Structural ceramics and functional ceramics.