MXene-derived TiB2 formation in B4C at high temperatures

Abstract Two-dimensional (2D) MXenes are nanometer-thick sheets of transition metal carbides, nitrides, or carbonitrides with high-temperature capabilities. MXenes can be used as nanofillers and functional additives in ceramic hybrids, enhancing sintering and mechanical and electrical properties. In this study, we systematically investigate the incorporation of titanium carbide (Ti 3 C 2 T x ) MXene into micron-sized (~ 6 μm) boron carbide (B 4 C) using a one-step electrostatic self-assembly method. We tuned the zeta potential of B 4 C and Ti 3 C 2 T x MXene solutions, gradually added B 4 C into the MXene solution, and prepared green bodies with 1 to 10 vol.% Ti 3 C 2 T x . We examined MXene phase stability, reactions, and phase transformation in B 4 C via direct current spark plasma sintering at 1925 °C with a pressure of 70 MPa in a vacuum. To understand the reaction pathways, we conducted stepwise sintering from 800 °C to 1800 °C in 200 °C increments. X-ray diffraction and scanning electron microscopy results revealed that Ti 3 C 2 T x reacts with B 4 C at ~ 1200 °C to form TiB 2 , with complete conversion at 1800 °C, resulting in a TiB 2 -B 4 C structure. For samples with 4 vol.% MXene or higher, B 2 O 3 formed above 1200 °C due to MXene oxygen terminations and disappeared above 1800 °C. The overall oxygen content in MXene-containing samples was lower than in B 4 C sintered without MXene, indicating its reducing nature as a 2D carbide. MXene also acts as a sintering additive and the relative density was increased by increasing the MXene content, achieving 99% with 10 vol.% MXene. The measured hardness values were 20 ± 1.6 GPa and 41 ± 0.8 GPa for B 4 C and B 4 C with 10 vol.% MXene Ti 3 C 2 samples, respectively. This trend indicates that increasing Ti 3 C 2 T x MXene content (1–10 vol.%) in the B 4 C matrix enhances hardness due to the formation of TiB 2 phases, which improves densification and reinforces the B 4 C matrix. Compared to traditional bulk TiC, 2D MXene sheets provide a larger surface area and uniform coverage of B 4 C particles, lowering diffusion energy and enhancing sintering rates. This study demonstrates a new approach to using MXene as a nanometer-thick additive to form uniformly distributed TiB 2 in B 4 C to enhance its structural properties.