Hot oscillatory pressing (HOP) is an advanced sintering technique for producing high mechanical performance ceramics; however, the underlying mechanism by which oscillatory pressure promotes densification and microstructural refinement remains inadequately understood. In this study, hysteresis analysis, adapted from metal fatigue models, was first applied to monitor the sintering behavior of Al₂O₃/TiC_p composites in real time. Densification curves and hysteresis loops indicate that grain boundaries exhibit viscoelastic characteristics when grain boundary sliding dominates, and the oscillatory pressure optimizes sintering through cyclic softening and hardening. Initially, a softening process promotes grain boundary sliding to accelerate densification. As density increases, energy dissipation due to internal friction induces a transition to cyclic hardening, thereby enabling simultaneous microstructural refinement and property enhancement. Microstructural analysis further reveals that, compared to static pressure, oscillatory pressure reduces grain boundary energy, inhibits grain growth, and enhances densification. The HOP-sintered composite exhibits a Vickers hardness of 21.8±0.3 GPa and flexural strength of 795±29 MPa, improvements of ∼10% and 21.4%, respectively, over hot pressing (HP). This work establishes a mechanistic framework linking oscillatory pressure to microstructural evolution, providing theoretical support for the further development of HOP technology.

In this work, a novel process, oscillatory pressure-assisted sinter forging (OPSF), for the preparation of high-performance ceramic composites was reported. Compared with the samples made by conventional sinter forging (SF) and hot oscillatory pressing (HOP), the SiC whisker reinforced Al₂O₃ composites (SiC_w–Al₂O₃) prepared by OPSF at the same temperature exhibited a higher density and significantly improved the mechanical properties. The improvements in densification and performance are attributed to simultaneous enhanced shear deformation at both macro- and micro-scales, resulting from the combination of die-free configuration and oscillatory pressure of OPSF. And the strength of grain boundary is greatly increased when the temperature reaches 1600 ℃ of OPSF, due to that the grain-boundary sliding became pronounced at higher temperatures. The current results shed light on a powerful technique for preparing ceramic composites, which is likely applicable to other systems.

Alumina whisker reinforced zirconia ceramic composite was prepared by both hot oscillatory pressing (HOP) and conventional hot pressing (HP). The results show that compared with HP, HOP can significantly increase the final density and densification rate of the material. Analysis of densification kinetics reveals that the predominant densification mechanism transits from grain boundary sliding in the beginning to the diffusion in the later stage. The main effect of the oscillating pressure is to increase the densification rate in the process of grain boundary sliding. The current study suggests that HOP is a promising technique for densifying whisker reinforced ceramics.