Abstract
AbstractSilicon carbide possesses exceptional mechanical and thermal properties, but its densification by conventional sintering is often very difficult. In the present work, silicon carbide was consolidated by spark plasma sintering in the presence of alumina and yttria. The results pointed out that the use of a single oxide does not enhance the sintering kinetics significantly, while the contemporaneous addition of both oxides has a beneficial effect on densification, with a relative density increase of about 10%. Interestingly, the oxide doping allows to double the room‐temperature flexural strength.
Highlights
The results pointed out that the use of a single oxide does not enhance the sintering kinetics significantly, while the contemporaneous addition of both oxides has a beneficial effect on densification, with a relative density increase of about 10%
Sintering cycle SPS1 can be considered as a conventional high-temperature spark plasma sintering (SPS) cycle for Silicon carbide (SiC); the specimens were heated up to 2300°C, and 60 MPa pressure was applied starting from 1200°C
One can observe a peak at about 1200°C for both materials, which is associated with the rearrangement of the powder determined by the pressure application
Summary
Silicon carbide (SiC) is a covalent ceramic characterized by unique combination of physical and mechanical properties (ie, low density, high hardness,[1] high elastic modulus,[2] low nuclear activation,[3] low thermal expansion coefficient, high-temperature strength4), which make it an optimum candidate for very different applications.[1,2] its sinterability is relatively limited and the consolidation of SiC-based components usually requires sophisticated and expensive technologies such as hot pressing (HP)[5] or hot isostatic pressing (HIP).[6]Over the years, alternative sintering techniques have been developed with the aim to reduce dwell time and temperature such as field-assisted sintering techniques (FAST) and, in particular, spark plasma sintering (SPS).[7,8,9]Spark plasma sintering consists of a mechanical loading system such as HP, but instead of an external heating, a pulsed electric current flows through the punches, through the mold, and, depending on the electrical conductivity, through the powder compact within the die.[10]. SPS allows to increase the heating rates with respect to HP and, allows a reduction of the processing time.[7,8,9] The current flow can significantly improve the mass transfer by other athermal mechanisms involving diffuse electrical field, thermo-diffusion,[11] electromigration,[12,13] and/or spark plasma formation,[14] the formation of plasma being still under debate.[15,16] High heating rates, short processing times, and low temperatures are possible with SPS, and this allows the production of highly densified materials with good control of grain coarsening. SiC densification by SPS has been extensively studied to point out the impact of processing parameters, such as pressure, holding time, and temperature, on densification.[17,18]
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