Fabrication of dense Cr₃AlB₄ polycrystals via pressure-assisted reactive sintering

This research investigates the synthesis of Cr₃AlB₄, a member of the MAB phase family, using the hot pressing (HP) method. Cr₃AlB₄ exhibits a combination of ceramic-like hardness and metal-like damage tolerance, making it valuable for applications in extreme environments. However, its synthesis is challenging due to phase transitions involving precursors. The study evaluates the influence of reaction sintering and annealing time on phase formation, grain growth, and material stability.

The results show that HP yields materials with over 80 % Cr₃AlB₄ phase content, but prolonged annealing leads to its decomposition into Cr₃B₄, which causes microstructural changes and grain cracking. Cracking is attributed to the differences in thermal expansion coefficients between Cr₃AlB₄ and other phases, leading to stress accumulation during cooling. To optimize the synthesis process, the study recommends controlling grain size and using non-reactive sintering additives to limit grain growth.