Densification mechanisms during high-pressure sintering of nanocrystalline Gd2Zr2O7 ceramic

High-pressure sintering (HPS) is a promising technique for producing nanocrystalline ceramics with unique properties. However, the densification mechanisms of HPS for nanocrystalline ceramics at different sintering stages remain controversial. This study focuses on Gd2Zr2O7 (GZO) nanocrystalline ceramics, investigating their microstructure evolution and densification behavior under varying pressures, temperatures, and dwelling times. The HPS process involves distinct stages: cold compaction, hot compaction, and isothermal progression. During cold compaction, densification is driven by the breakdown of aggregates, particle rearrangement, and local plastic deformation, resulting in a relative density of 84.8%. The intermediate stage achieves an increase to ∼93.7% in relative density by grain boundary-mediated plastic deformation mechanism. The final isothermal stage, held at 500 °C / 5 GPa, achieves nearly full density (∼99.2%) through diffusion creep, eliminating microstructural defects. This comprehensive understanding of HPS densification mechanisms, exemplified by GZO ceramics, contributes to advancing nanocrystalline ceramic applications.