Pivotal Role of A-Site Elements in the Stability and Mechanical Properties of h-MAB Phases

Hexagonal MAB (h-MAB) phases, a novel class of metal-ceramic materials, have garnered significant attention in the scientific community due to their promising mechanical properties and thermal stability. In this study, we performed computational analyses of both predicted and experimentally synthesized h-MAB phases, providing a comprehensive overview of their structural and mechanical characteristics. For the first time, we systematically explored the structural stability mechanisms of these phases and examined the influence of A-site elements─both metals and nonmetals─on their mechanical properties. Based on the proportion and the interaction relationship of BM₆octahedron, AM₆trigonal prisms and boron rings, we proposed two different stabilization mechanisms of h-MAB phases. Furthermore, the A-site element has a significant impact on the mechanical properties of h-MAB phases. Nonmetallic A-site elements enhance the mechanical strength, whereas metallic A-site elements like cadmium (Cd) impart notable toughness and ductility. These findings offer valuable insights into the design and optimization of h-MAB phases, which provides a framework for tailoring their mechanical properties and advancing the field of MAB materials.