15. - 17. 5. 2013, Brno, Czech Republic, EU PREPARATION OF MULTIPHASE MATERIALS WITH SPARK PLASMA SINTERING Radek MUŠÁLEK, Zdeněk DLABÁČEK, Monika VILÉMOVÁ, Zdenek PALA, Jiří MATĚJÍČEK, Tomáš CHRÁSKA Institute of Plasma Physics AS CR, v.v.i., Za Slovankou 1782/3, 182 00 Prague, Czech Republic musalek@ipp.cas.cz Abstract Spark plasma sintering (SPS), also called Field Assisted Sintering Technique (FAST), represents a novel method of preparation of sintered materials from powders. The main advantage of the SPS method is a high achievable heat rate (>200 °C/min) and high sinteri ng temperatures (up to 2200 °C in our laboratory). Combination of high heating rate, rather high pressures (up to 80 MPa) and electric field fluctuations leads to an effective sintering and significant reduction of sintering time for both coarse-grained and nanocrystalline powders. Composite materials may be easily obtained by mixing or layering of different powders. The paper will introduce several examples of multiphase materials sintered by SPS at our institute and the establishment of procedures for routine testing of sub-sized specimens. Keywords: spark plasma sintering, powder metallurgy, composites, multiphase materials, FeAl matrix 1. INTRODUCTION In many applications, conventional materials have already reached their limits. One of the possibilities how to withstand extreme service conditions is to prepare multiphase materials in which properties of two (or more) materials are combined. Such an example may be the reinforcement of ductile primary phase (matrix) with a hard secondary phase, which can increase the material’s hardness or wear resistance. Usually, the properties of both phases are quite different and finding optimum sintering conditions may be challenging. One of the possibilities of effective preparation of multiphase materials is the SPS method where multiphase materials may be prepared by simple mechanical mixing and/or subsequent layering of the input materials (powders). Layering may be used in cases when both the internal cohesion of individual layers as well as mutual bonding of the layers can be achieved. By gradual change of the volumetric ratio of powder mixing for each layer, even functionally graded materials may be effectively introduced. On the other hand, for the mechanical mixtures, only sintering of the dominant phase is necessary and matrix reinforced by a second phase may be easily produced in this way. The SPS method enables effective preparation of multiphase materials in laboratory conditions as very small amounts of materials are needed (in our laboratory typically about 5 grams per one sintered sample). The principle of SPS is quite simple – powder or powders are placed between two graphite punches and constrained by a graphite die. The material is compressed and internally heated by Joule’s heat generated by pulsed direct current passing directly through the punches, die and the powder. No external heating elements are therefore needed which significantly decreases the overall thermal capacity of the heated volume and enables extremely high heating rates and short sintering times and effectively reduces grain growth. Vacuum or protective atmosphere in the sintering chamber helps to out-gas the heated powders and improves overall purity of the sintered compacts. On the other hand, many issues connected with SPS are still not solved, e.g. detailed models of sintering mechanisms, plasma formation in the sintered materials, optimum way of avoiding carbon contamination from the dies, formation of carbides, temperature reading in the process zone, etc. More details about SPS technology and its possibilities are provided e.g. in [1,2].