Preparation of B4C–SiC composite ceramics through hot pressing assisted by mechanical alloying

• Disordered B4C–SiC composite powders with high sintering activity were fabricated.
• Dense B4C–SiC composite ceramics were obtained under a relatively low temperature.
• Order–disorder transformation during mechanical alloying and sintering was verified.
• Specific toughening mechanism of B4C–SiC composites was studied.
• Role of disorder–order transformation-driven sintering of ceramics was demonstrated.

In order to prepare dense B4C–SiC composites under relatively low temperature without any additive, stacking disordered B4C–SiC ultrafine composite powders were fabricated by mechanical alloying firstly. Subsequently, hot pressing sintering was applied to produce a dense B4C–SiC composite under relatively low temperature (1800–1950 °C) without any additive. For the samples sintered at 1950 °C for 30 min, the obtained relative density, Vickers hardness, flexural strength and fracture toughness were 96%, 24 GPa, 430 MPa, and 4.6 MPa.m1/2, respectively. The microstructural characterization showed that the main fracture mode was transgranular. The transgranular facture is caused by the powerful interfacial bonding between B4C and SiC. The density of the samples sintered with composite powders was 13% higher than the density of the samples sintered with mixed powders under the same conditions, indicating that the composite powders had an improved sintering activity due to their disordered structure. Meanwhile, the role of disorder–order transformation-driven sintering of ceramics was demonstrated.