Enhancing efficiency of field assisted sintering by advanced thermal insulation

The influence of advanced thermal insulation on energy consumption and temperature distribution during electric field assisted sintering of conductive stainless steel powder and non-conductive zirconia powder was investigated. Four types of tool setup were considered: i) without insulation, ii) with die wall insulation, iii) with additional insulation of die faces and iv) with spacers manufactured from carbon fiber reinforced carbon composite (CFRC). The influence of thermal insulation on energy consumption was experimentally studied for samples with diameter of 17 mm. The temperature distribution in samples with diameters of 17 mm, 50 mm and 150 mm was modeled using the Finite Element Method. The power consumed during dwell was almost half the value when die wall insulation was used. The additional insulation of die faces and the application of CFRC spacers provide a threefold decrease in power during sintering of steel powder and a fivefold reduction during sintering of zirconia powder. The advanced thermal insulation significantly homogenizes the temperature distribution within samples of small and medium size. The advanced thermal insulation provides a strong decrease in the temperature gradient inside large conductive sample with a diameter of 150 mm. However, insulation apparently cannot ensure acceptable temperature homogeneity within non-conductive parts of such diameter. The reason for this is the specific current path and related heat concentration near the sample edge.