Field assisted sintering technique/spark plasma sintering (FAST/SPS) is a well known method for sintering of ceramic and metal powders. Due to rapid heating to sintering temperature, the process is discussed to be highly efficient, but enhanced energy consumption and inhomogeneous temperature distribution especially in the case of non-conductive powders remain the challenging tasks. In the present work, a detailed study was conducted to demonstrate the advantage of advanced thermal insulation of the graphite tool on energy consumption and temperature distribution during the FAST/SPS cycle. Four types of experimental setup were considered in the study: i.) graphite tool without insulation as reference ii.) die wall insulation by graphite felt iii.) die wall insulation with additional insulation of both die faces iv.) setup iii.) in combination with specific protection plates made of carbon fiber reinforced carbon (CFRC) known for its much lower thermal conductivity compared to conventional graphite plates. To see the influence of the sample conductivity on energy consumption and temperature distribution, electrically conductive 316L steel powder and non-conductive 8YSZ ceramic powder were used for the study. All experiments were done on samples with a diameter of 17 mm. In addition, FEM modelling was used to study the change of temperature distribution if the sample diameter was enlarged to 50 mm and 150 mm.
Our study showed that the energy consumption can be significantly reduced by applying the measures described before. With setup iv.) it could be demonstrated that the energy demand was reduced by a factor of 3 for conductive 316 L powder and by a factor of 5 for non-conductive 8YSZ powder. Another positive effect of the advanced thermal insulation is the clearly improved homogenization of the temperature field, which leads to significant improvement of properties distribution within sintered samples. Nevertheless, if combination of non-conductive powders and large sample dimensions is considered, limitations of traditional FAST/SPS setups became obvious.