Understanding the lower fracture resistance of cold sintered ceramics

The cold sintering process (CSP) enables densification of ceramics at unprecedented low temperatures, unlocking unique opportunities in microstructural design. However, the mechanical behaviour of cold sintered ceramics remains unexplored. This study aims to compare the mechanical strength and fracture resistance of cold sintered (140°C) with conventionally sintered (1000°C) ZnO. The effect of grain size is investigated in samples sintered using conventional, cold and rapid sintering. It was found that cold sintered ZnO exhibits ∼50 % lower strength compared to conventionally sintered parts (∼120 vs. ∼240 MPa). This is explained by the lower fracture toughness of the former (0.57 vs. 1.15 MPa·m 1/2 ), resulting from a grain size effect that favours intergranular fracture along nanometric grains. This grain size effect is supported by the higher hardness measured on cold vs. conventionally sintered ZnO (4.5 vs. 1.8 GPa). The lower toughness of cold sintered ceramics is demonstrated to be related to their nanocrystalline nature.