advanced equipment for powder metallurgy research-discharge plasma sintering system (SPS)

With the development of high-tech industry, the types and demands of new materials, especially new functional materials, are increasing, and the new functions of materials call for new preparation technologies. Spark Plasma Sintering (SPS) is a brand-new technology for preparing functional materials. It has the distinct characteristics of fast heating speed, short sintering time, controllable microstructure, energy saving and environmental protection, and can be used to prepare metal materials, ceramic materials, composite materials, nano-bulk materials, amorphous bulk materials, gradient materials and so on.

development and application of SPS at home and abroad

SPS technology is heating and sintering by directly introducing pulse current between powder particles, so it is also called plasma activated sintering or plasma-assistedsintering-PAS in some literatures. As early as 193, American scientists put forward the principle of pulse current sintering, but it was not until 1965 that pulse current sintering technology was applied in the United States, Japan and other countries. Japan obtained the patent of SPS technology, but at that time it failed to solve the problems of low production efficiency, so SPS technology was not popularized and applied.

in p>1988, Japan developed the first industrial SPS device, which was widely used in the research field of new materials. After 199, Japan introduced the third generation SPS product which can be used in industrial production, with a sintering pressure of 1 ~ 1t and a pulse current of 5, ~ 8,a. Recently, a large SPS device with a pressure of 5t and a pulse current of 3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[15A has been developed. Due to the advantages of SPS technology, such as high speed, low temperature and high efficiency, in recent years, many foreign universities and scientific research institutions have successively equipped SPS sintering systems, and used SPS to research and develop new materials, and introduced several SPS sintering systems, which are mainly used to sinter nano-materials and ceramic materials [5 ~ 8]. As a new technology of material preparation, SPS has attracted extensive attention at home and abroad.

sintering principle of SPs

3.1 plasma and plasma processing technology [9,1]

SPS is sintered by using discharge plasma. Plasma is a state of matter under high temperature or specific excitation, and it is the fourth state of matter except solid, liquid and gas. Plasma is an ionized gas, which is composed of a large number of positive and negative charged particles and neutral particles and shows collective behavior.

plasma is a dissociated high-temperature conductive gas, which can provide a state with high reactivity. The temperature of plasma is 4 ~ 1999℃, its gaseous molecules and atoms are highly activated, and the degree of ionization in plasma gas is very high, which makes plasma a very important material preparation and processing technology.

plasma processing technology has been widely used, such as plasma CVD, low temperature plasma PBD, plasma and ion beam etching. At present, plasma is mostly used in oxide coating and plasma etching, and also has some applications in preparing high-purity carbide and nitride powders. Another potential application field of plasma is the sintering of ceramic materials [1].

the methods of generating plasma include heating, discharging and light excitation. Plasma produced by discharge includes DC discharge, RF discharge and microwave discharge plasma. SPS uses DC discharge plasma.

SPS device and basic principle of sintering

SPS device mainly includes the following parts: axial pressure device; Water-cooled punch electrode; Vacuum cavity; Atmosphere control system (vacuum, argon); DC pulse and cooling water, displacement measurement, temperature measurement, and safety control units. The basic structure of SPS is shown in Figure 1.

SPS is similar to hot pressing (HP), but the heating mode is completely different. SPS is a pressure sintering method which uses on-off DC pulse current to directly energize sintering. The main functions of on-off DC pulse current are to generate discharge plasma, discharge shock pressure, Joule heat and electric field diffusion [11]. When SPS is sintered, pulse current passes through powder particles as shown in Figure 3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1. During SPS sintering, the instantaneous discharge plasma generated when the electrode is energized with DC pulse current makes each particle in the sintered body generate Joule heat uniformly and activate the particle surface. Similar to SHS and microwave sintering, SPS is sintered by effectively utilizing the self-heating effect inside the powder. SPS sintering process can be regarded as the comprehensive result of particle discharge, conductive heating and pressurization. In addition to heating and pressure, in SPS technology, the effective discharge between particles can produce local high temperature, which can melt the surface locally and peel off the surface substances. Sputtering and discharge shock of high temperature plasma remove impurities (such as removing surface oxides, etc.) and adsorbed gases on the surface of powder particles. The function of electric field is to accelerate the diffusion process [1, 9, 13]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1].

technological advantages of SPS

The technological advantages of SPS are obvious: uniform heating, high heating speed, low sintering temperature, short sintering time, high production efficiency, fine and uniform product structure, natural state of raw materials, high-density materials, gradient materials and complex workpieces [3, 11]. Compared with HP and HIP, SPS device is simple to operate and does not need special skilled technology. Literature [11] reported that the total time for producing a piece of ZrO _ 3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1 (3y)/stainless steel gradient material (FGM) with a diameter of 1mm and a thickness of 17mm was 58min, including heating time of 3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[18min, heat preservation time of 5min and cooling time of 3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[15min. Compared with HP, the sintering temperature of SPS technology can be reduced by 1 ~ 3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1℃ [13].

application of SPS in material preparation

at present, many researches on preparing new materials with SPs have been carried out abroad, especially in Japan, and some products have been put into production. The types of materials that SPS can process are shown in Table 1. In addition to preparing materials, SPS can also carry out material connection, such as connecting MoSi3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1 _ 3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1 with stone mill [14], ZrO _ 3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1/Cermet/Ni and so on [15].

In recent years, the research on preparing new materials by SPS at home and abroad mainly focuses on ceramics, cermets, intermetallic compounds, composite materials and functional materials. Among them, functional materials are the most studied, including thermoelectric materials [16], magnetic materials [17], functionally graded materials [18], composite functional materials [19] and nano-functional materials [3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1]. The preparation of amorphous alloy, shape memory alloy [3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[11] and diamond by SPS was also tried, and good results were obtained.

gradient materials

The composition of functionally graded materials (FGM) varies in gradient, and the sintering temperature of each layer is different, so it is difficult to sinter at one time by using the traditional sintering method. It is very expensive to prepare gradient materials by CVD, PVD and other methods, and it is difficult to realize industrialization. Using a stepped stone mill die, because the current density at the upper and lower ends of the die is different, a temperature gradient can be generated. Using the gradient temperature field generated by SPS in the stone mill mold, gradient materials with different composition ratios can be sintered in just a few minutes. At present, the gradient materials successfully prepared by SPS are: stainless steel/ZrO3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1; Ni/ZrO3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1； Al/ polymer; Al/ plant fiber; PSZ/T gradient materials.

in SHS, the electric field has a great activation effect and function, especially the field activation effect can successfully synthesize materials that could not be synthesized before, expand the composition range, and control the phase composition, but the obtained porous materials need further processing to improve the density. Using SPS technology similar to SHS electric field activation, ceramics, composites and gradient materials can be synthesized and densified at the same time, and 65nm nanocrystals can be obtained, which is one less densification step than SHS [3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[13]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1]. Large-sized FGM can be prepared by SPS. At present, the large-sized FGM system prepared by SPS is ZrO _ 3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1 (3y)/stainless steel disk, and the size has reached 1mm×17mm[3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[13].

additives must be added when using ordinary sintering and hot pressing WC powder, and SPS makes it possible to sinter pure WC. The Vickers hardness (HV) and fracture toughness of WC/Mo gradient materials prepared by SPS reached 3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[14Gpa and 6 MPa M1/3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1, respectively, which greatly reduced the cracking caused by thermal stress due to thermal expansion mismatch between WC and Mo [3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[14].

thermoelectric materials

Recently, thermoelectric converters have attracted great interest because of their high reliability and pollution-free, and many thermoelectric conversion materials have been studied. According to the literature search, it is found that there are many researches on thermoelectric materials in the preparation of functional materials by SPS.

(1) The composition gradient of thermoelectric materials is one of the effective ways to improve the efficiency of hot spots. For example, βFeSi3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1 with gradient composition is a promising thermoelectric material, which can be used for thermoelectric conversion between 3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1 ~ 9℃. βFeSi3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1 is non-toxic, has good oxidation resistance in air, and has high conductivity and thermoelectric power. The higher the quality factor of hot spot materials (Z=α3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1/kρ, where z is quality factor, α is Seebeck coefficient, k is thermal conductivity coefficient, and ρ is material resistivity), the higher the thermoelectric conversion efficiency. The test shows that the thermoelectric performance of β FeSIX (with variable Si content) with composition gradient prepared by SPS is much higher than that of βFeSi3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1 [3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[15]. Examples of this are Cu/Al3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1O3/Cu [3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[16], Mgfesi3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1 [3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[17], β Zn4Sb3 [3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[18], tungsten silicide []3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[19] and so on.

(3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1) The traditional semiconductor materials used for thermoelectric refrigeration not only have poor strength and durability, but also are mainly prepared by single-phase growth method, which has long production cycle and high cost. In recent years, in order to solve this problem, some manufacturers use sintering method to produce semiconductor refrigeration materials. Although the mechanical strength and material utilization rate are improved, the thermoelectric performance is far from that of single crystal semiconductors. Now, using SPS to produce semiconductor refrigeration materials, a complete semiconductor material can be prepared in a few minutes, while the crystal growth takes more than ten hours. The advantage of preparing semiconductor thermoelectric materials by SPS is that it can be directly processed into circular pieces, without cutting processing like unidirectional growth method, which saves materials and improves production efficiency.

the properties of hot pressed and cold pressed-sintered semiconductors are lower than those prepared by crystal growth method. At present, the main components of semiconductor materials used for thermoelectric refrigeration are Bi,Sb,Te and Se. At present, the highest Z value is 3.×1/K, while the Z value of thermoelectric semiconductors prepared by SPS has reached 3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1.9 ~ 3.× 1/k, which is almost equal to the performance of single crystal semiconductors [3]. Table 3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1 is a comparison between SPS and other methods to produce BiTe materials.

ferroelectric materials

when sintering ferroelectric ceramics PbTiO3 with SPS, it is sintered at 9 ~ 1℃ for 1 ~ 3min, and the average particle size after sintering is <: 1μm, and the relative density is over 98%. Because there are few holes in ceramics [31], the dielectric constant does not change with frequency between 11 and 16 Hz.

when the ferroelectric material Bi4Ti3O13]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1 ceramics are prepared by SPS, the grains of the sintered body are elongated and coarsened, and the ceramics are rapidly densified. Samples with good grain orientation can be easily obtained by SPS, and it can be observed that the electrical properties of Bi4Ti3O13]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1 ceramics with preferred grain orientation have strong anisotropy [33]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1].

replacing IIVI semiconductor ZnO ceramics with ferroelectric Li prepared by SPS can increase the ferroelectric phase transition temperature Tc to 47K, compared with 33K[34] in the previous cold-pressed sintered ceramics.

magnetic materials

Nd Fe B magnetic alloy sintered by SPS can obtain high density if sintered at a higher temperature, but too high sintering temperature will lead to the appearance of α phase and grain growth, and the magnetic properties will deteriorate. If sintered at a lower temperature, the powder can maintain good magnetic properties, but it can not be completely compacted, so the relationship between density and properties should be studied in detail [35].

SPS has the technological advantages of low sintering temperature and short holding time when sintering magnetic materials. Nd Fe Co V B can be sintered into nearly completely dense bulk magnets after being kept at 65℃ for 5 minutes, and no grain growth is found [36]. The composite material of 865Fe6Si4Al35Ni and MgFe3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1O4 prepared by SPS (85℃, 13MPa) has high saturation magnetization Bs=13]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1T and high resistivity ρ = 1× 1Ω m [37].

Although the soft magnetic alloy ribbons prepared by rapid solidification method have reached a fine grain structure of tens of nanometers, they cannot be prepared into alloy blocks, and their application is limited. However, the magnetic properties of bulk magnetic alloys prepared by SPS have reached the soft magnetic properties of amorphous and nanocrystalline tapes [3].

nanomaterials

More and more attention has been paid to the preparation of compact nanomaterials. When preparing nano-materials by traditional hot pressing sintering and hot isostatic pressing sintering, it is difficult to ensure that nano-sized grains and complete compactness can be achieved at the same time. Using SPS technology, the grain coarsening can be significantly suppressed due to the fast heating speed and short sintering time. For example, TiN powder with an average particle size of 5μm can be sintered by SPS (1963K, 196 ~ 383]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1 MPa, 5min), and TiN dense body with an average grain size of 65nm can be obtained [3]. Reference [3] cited relevant examples to explain that the grain growth in SPS sintering was restrained to the maximum extent, and the sintered body produced had no porosity and obvious grain growth.

during SPS sintering, although the applied pressure is small, besides the pressure, the activation ability Q will be reduced, and the Q value will be further reduced due to the discharge, which will promote the grain growth. Therefore, it is difficult to prepare nano-materials by SPS sintering.

however, there are actually examples of successfully preparing TiN dense entities with an average particle size of 65nm. In reference [38], amorphous powder was sintered by SPS to prepare 3]。1998年瑞典购进SPS烧结系统，对碳化物、氧化物、生物陶瓷等材料进行了较多的研究工作[4]。

国内近三年也开展了用SPS技术制备新材料的研究工作[1 ~ 3 nm Fe9Zr7B3 nano-magnetic materials. In addition, it has been found that the grain changes slowly with SPS sintering temperature [7], so the mechanism of preparing nano-materials by SPS and its influence on grain growth need to be further studied.

preparation of amorphous alloy

in the preparation of amorphous alloy, the alloy composition should be selected to ensure that the alloy has a very low critical cooling rate of amorphous formation, so as to obtain a very high amorphous formation ability. In the preparation process, there are mainly metal casting method and water quenching method, and the key is to quickly cool and control uneven nucleation. Because the technology of preparing amorphous alloy powder is relatively mature, for many years, bulk amorphous alloy has been prepared by warm extrusion, warm rolling, impact (explosion) curing and isostatic pressing sintering of amorphous powder below its crystallization temperature, but there are many methods.