Field-Assisted Sintering Technology / Spark Plasma Sintering

场辅助烧结技术/火花等离子体烧结（FAST/SPS）是一种独特的技术，用于在高温下合成和烧结无机材料，将单轴压力与脉冲直流电相结合。电压低（低于10 V），但电流高（通常为1至10 kA），当电流流过放置无机粉末的石墨模具时，导致有效的焦耳加热。这些条件允许实现高达1000 K/min的加热速率，尽管通常在50 - 200 K/min的范围内，其远高于其他常规烧结技术如无压烧结和热压的加热速率（约20 K/min）。等温保持时间大大缩短，仅在几分钟内样品就完全致密化，而其他技术则需要几个小时的停留时间才能达到相同的目的。因此，FAST/SPS可在短短几分钟内使材料完全致密化，限制甚至抑制晶粒生长，从而定制微观结构。通常，石墨工具用于容纳粉末，因为其具有高导电性和导热性以及高熔点（烧结至约100 ° C）。2500 K）。另一方面，石墨工具限制最大单轴压力（通常高达75 MPa），并且需要使用保护气氛，例如真空或氩气。然而，非石墨工具是以降低最高温度为代价来增加单轴压力的替代方案。FAST/SPS是一种多功能的技术，可导致多种材料、微结构和结构的固结。金属和陶瓷可以被烧结，而不受其固有的电或热特征的任何限制，包括金属间化合物、超合金、难熔金属、超高温陶瓷（UHTC）、透明陶瓷、碳化物、氮化物、硼化物、氧化物、MAX相和非平衡材料。重要的是，合成也可以在烧结过程中进行，这被称为反应烧结，开发出其他方法无法生产的完全致密的化合物。此外，由于加热条件的特性，可以控制微观结构以赋予不同的性能。关于结构，具有受控孔隙率的多孔结构、块体材料、陶瓷基复合材料以及金属和陶瓷的连接可以通过FAST/SPS获得，由于热循环短（几分钟而不是几小时），避免了不同组分之间的化学反应。

Field-Assisted Sintering Technology/Spark Plasma Sintering (FAST/SPS) is a unique technique for the synthesis and sintering of inorganic materials at high temperature that combines uniaxial pressure with a pulsed direct current. The voltage is low (below 10 V), but the current is high (typically from 1 to 10 kA), leading to efficient Joule heating as the current flows through the graphite dies where the inorganic powder is placed. These conditions allow to achieve heating rates up to 1000 K/min, although typically in the range 50 – 200 K/min, which are much higher than the heating rates (around 20 K/min) of other conventional sintering techniques such as pressureless sintering and hot pressing. The isothermal holding time is strongly reduced and just in a few minutes the sample is fully densified, meanwhile other techniques require several hours during the dwell time for the same purpose. Consequently, FAST/SPS leads to fully densify materials in just a few minutes, limiting – or even inhibiting - the grain growth and thus, tailoring the microstructure. Typically, graphite tools are used to contain the powders due to the high electrical and thermal conductivity as well as the high melting point (sintering up to approx. 2500 K). On the other hand, the graphite tools limit the maximal uniaxial pressure (typically up to 75 MPa) and require to use protective atmosphere such as vacuum or argon. Nevertheless, non-graphite tools are an alternative to increase the uniaxial pressure at expenses of reducing the maximal temperature. FAST/SPS is a versatile technique that leads to consolidate a manifold of materials, microstructures and structures. Metals and ceramics can be sintered, without any restriction due to their intrinsic electrical or thermal features, including intermetallics, superalloys, refractory metals, ultra-high temperature ceramics (UHTCs), transparent ceramics, carbides, nitrides, borides, oxides, MAX phases, and non-equilibrium materials. Importantly, synthesis can be also performed during the sintering process, which is called reactive sintering, developing fully dense compounds that cannot be produced by other methods. Furthermore, due to the characteristics of the heating conditions, the microstructure can be controlled to confer different properties. Regarding the structures, porous architectures with controlled porosity, bulk materials, ceramic matrix composites and joining of metals and ceramics can be obtained by FAST/SPS, avoiding the chemical reaction between different components due to the short thermal cycles (minutes instead hours).