Effect of plunger exposed length on densification uniformity and microstructural evolution of liquid-phase-sintered SiC ceramics during spark plasma sintering

Plunger exposed length was used to tailor SPS processing of SiC ceramics. • Reducing the exposed length lowered resistance and advanced shrinkage onset. • Edge under-sintering was reduced without changing composition or schedule. • Residual edge oxides disappeared when the exposed length was decreased. • The balance between edge densification and center stability was clarified. In this work, SiC ceramics with Al 2 O 3 and CeO 2 sintering additives were prepared by spark plasma sintering (SPS). The exposed length of the upper plunger, H, was adjusted to 15, 12, and 9 mm by changing the relative position of the die assembly. The effect of H on densification, microstructure, and local mechanical properties was investigated. As H decreased from 15 to 9 mm, the initial system resistance decreased by about 19%, the onset shrinkage temperature decreased from 1631 ± 10 °C to 1535 ± 10 °C, and the relative density increased from 95.94% to 98.20%. This change in electrical response is considered to alter the current and Joule heat distribution in the graphite tooling, thereby improving the local sintering condition and liquid-phase-assisted densification near the sample edge. Accordingly, the edge of S-H15 was too porous for valid hardness measurement, whereas the S-H9 edge reached 22.91 ± 0.09 GPa. However, fine pores remained in the center of S-H9, where the hardness decreased to 19.75 ± 0.16 GPa. These results show that plunger exposed length is an important tooling parameter affecting regional densification during SPS of SiC ceramics. Download: Download high-res image (238KB) Download: Download full-size image