Tailoring the thermal and thermomechanical characteristics of novel MAX phase boron composites in high-temperature applications.

MAX phase composites are gaining great attention for their excellent attributes in high-temperature applications like aerospace, energy, and nuclear industries. However, tailoring their thermal and thermomechanical properties for better performance at elevated temperatures remains a significant challenge. Therefore, the aim of this study is to synthesize novel MAX phase boron (B) composites for high-temperature applications. Titanium aluminum nitride (Ti₄AlN₃) and titanium aluminum carbide (Ti₃AlC₂) MAX phase reinforced B composites were prepared using the hot-pressing method at three different sintering temperatures: 1050 °C, 1250 °C, and 1325 °C. Thermal stability, thermal conductivity and thermomechanical properties of MAX phase composites were investigated through thermogravimetric analysis (TGA), hot disk method, and thermomechanical analyzer (TMA). The results reveal that thermal stability and thermal conductivity increased with rising sintering temperatures for both MAX composites. This is because higher sintering temperatures enhance atomic diffusion, densification, and particle bonding, leading to improved thermal stability and thermal conductivity of the composite. Moreover, the thermal stability of the Ti₄AlN₃ composite is higher than that of the Ti₃AlC₂ composites. At 1325 °C sintering, Ti₃AlC₂ composites remain stable up to 600 °C with 1.4% weight loss, while the Ti₄AlN₃ composite shows better stability up to 700 °C with only 0.6% weight loss. These MAX phase composites also show varying coefficients of thermal expansion (CTEs) at different temperature ranges, indicating that their thermal expansion properties are highly dependent on sintering temperatures. Both MAX composites exhibit lower overall CTEs at higher sintering temperatures, suggesting enhanced thermal stability. The negative CTEs at higher sintering temperatures in both materials suggest unusual thermal behavior, possibly due to phase transitions, secondary phase formation, or microstructural changes. These findings offer valuable insights into their thermal stability and decomposition characteristics, which are vital for high-temperature applications in electronics, optoelectronics, and semiconductor devices.