Subcritical crack growth in cold sintered ZnO ceramics

The long-term mechanical reliability of ceramic components is often compromised by the subcritical growth of defects (SCCG), especially under high relative humidity environments. In this study, structural degradation associated with SCCG is investigated for the first time in cold sintered ZnO and compared to counterparts of same density sintered at 1000°C. Constant stress rate experiments ranging between 0.001 MPa/s and 1000 MPa/s are performed in air and water for both samples. While both cold sintered and conventionally sintered ZnO ceramics are susceptible to SCCG in the same manner, the former exhibit a distinct threshold behaviour up to relatively high stress intensity levels (ca. 0.7$·$K_Ic). The effect of the nanoscale grain size and potential chemical effects associated with the cold sintering process on SCCG are discussed. The findings are supported by constant stress experiments and fractographic analyses, providing valuable insights for the mechanical design and lifetime assessment of cold sintered components.