High-pressure regulated phase transition enables in situ synthesis of high-performance dual-phase Si3N4 ceramics

• • Full densification of Si3N4 with only 5 wt% additives requires ≥150 MPa pressure at 1500 °C; 50 MPa SPS at 1600 °C fails, highlighting the necessity of high pressure for low-temperature processing. • • At 200 MPa and 1560 °C, stress-induced α→β phase transformation via coherent interface migration produces elongated β-columnar grains with embedded α particles, yielding a hardness of 21.3±0.3 GPa and toughness of 6.3±0.3 MPa·m1/2. • • The 150 MPa baseline exhibits grain coarsening and reduced toughness, demonstrating that higher pressure (200 MPa) is critical for grain refinement and property enhancement. • • The dual-phase microstructure achieves a superior hardness-toughness combination (21.3 GPa, 6.3 MPa·m1/2) compared to conventionally processed Si3N4, enabling applications in abrasive wear and high-temperature structural components.