Joining B₄C–TiB₂ ceramics with Ti interlayer via spark plasma sintering: Temperature-dependent interfacial microstructure and mechanical strength

To investigate the bonding behavior of SiC-free composite ceramics via spark plasma sintering (SPS), this study demonstrated the successful joining of B₄C–40 vol% TiB₂ ceramics with a Ti foil interlayer within the temperature range of 1000–1400 °C. The bonding mechanisms across temperatures were systematically elucidated through integrated approaches, including phase composition analysis, microstructural observation, and thermodynamic and diffusion kinetic calculations. The results revealed that the competitive reactions between active Ti and ceramic phases drive sequential compositional evolution at the joint interface. Starting from pure Ti, the interface transitioned to a mixture of TiB₂, TiC, TiB, and residual Ti, ultimately forming a stable TiB₂–TiC–TiB ceramic assemblage as the temperature increases. Kinetic analysis revealed that between 1000 and 1300 °C, the reaction layer thickness followed a diffusion-controlled growth model and was directly correlated with temperature via Arrhenius-type kinetics. At the highest temperature of 1400 °C, the complete consumption of Ti yielded a full-ceramic joint. Mechanical characterization indicated that these temperature-dependent microstructural changes significantly affected joint performance. The maximum shear strength of 72 MPa was achieved at 1300 °C, accompanied by crack penetration through the ceramic, reaction layer, and residual Ti layer during fracture.