Spark plasma sintering (SPS) is a new powder metallurgy sintering technology which is made of metal powder into graphite and other materials. The specific sintering power and pressing pressure are applied to the sintering powder by using the up and down die punching and power on electrodes. The high performance materials are made by discharge activation, thermoplastic deformation and cooling.
During SPS sintering, pulse current flows in from the indenter and the current flows into several directions; the current passing through graphite mold generates a large amount of heat, which is used to heat powder; through the current of sintering body, due to the gap between particles in the initial sintering stage, spark discharge will occur between adjacent particles, and some gas molecules are ionized, and the positive ions and electrons produced will be directed to cathode and electron respectively Anode movement, discharge between particles to form plasma; with the increasing of plasma density, the high-speed reverse movement particle flow will produce a large impact on the surface of particles, which can not only disperse the adsorbed gas or broken oxide film, but also purify and activate the surface of particles, which is conducive to the sintering of powder; the powder particles produce discharge at the non-contact part under the action of pulse electric field Electric heating, Joule heat is generated at the contact part, and the high temperature field formed in a moment causes the local melting of the particle surface; under the pressure, the melted particles are combined, and the local diffusion of heat makes the bonding parts bond together to form the sintering neck.
The traditional hot pressing sintering mainly consists of Joule heat and pressure generated by power on to produce plastic deformation and densification sintering of powder particles. SPS, in addition to the above-mentioned effects, also uses the plasma generated by the discharge between powder particles to make it self heated. SPS technology is a new technology for material preparation and processing, which is fast, energy-saving and environmental protection. It can effectively solve the problems of low density and large grain size in traditional sintering methods.
SPS technology has the advantages of the above, so it can be used to prepare metal materials, ceramics materials, composite materials, especially for the preparation of nano block materials, amorphous bulk materials, gradient materials, etc. For example, the composition of functionally graded materials is gradient changing, and the sintering temperature of each layer is different, so it is difficult to burn once by traditional sintering method. It is very expensive and difficult to realize industrialization by CVD and PVD. The gradient temperature field produced by SPS in the grinding die can be sintered well in a few minutes. At present, the gradient materials successfully prepared by SPS are stainless steel /zro2, ni/zro2, al/ polymer and other gradient materials.
The preparation of dense nano materials has been paid more and more attention. It is difficult to ensure that the nano size grains and the complete density can be achieved simultaneously when the traditional hot pressing sintering and hot isostatic sintering are used to prepare the nano materials. With SPS technology, the coarse grain can be inhibited significantly because of the high heating speed and short sintering time. For example, the tin dense solid with average grain size of 65nm can be obtained by SPS sintering (1963k, 196-382mpa, sintering for 5min). It is difficult to realize the bulk amorphous materials by ordinary powder metallurgy. SPS, as a new generation sintering technology, is expected to make progress in this field. The bulk (10 × 2mm) amorphous samples have been obtained by using SPs sintering from the amorphous Al based powders prepared by mechanical alloying.