Synthesis, microstructure and properties of MoAlB MAB phase films

MoAlB, given its remarkable properties of both metals and ceramics, has rekindled interest. In this study, MoAlB MAB phase films were fabricated using multi-target direct-current magnetron sputtering (DCMS) and ex-situ annealing, yielding fine, compact, and columnar-free structures. The microstructure evolution of as-deposited films during ex-situ annealing was elucidated. Results revealed that the as-deposited film was amorphous. After ex-situ annealing below 600 °C, the film presented a composite structure comprising nanocrystals embedded in an amorphous matrix, exhibiting the highest values for hardness and Young's modulus, namely 30 ± 2 GPa and 438 ± 15 GPa, respectively. At 600 °C, the film transformed from amorphous to a MoAlB MAB phase without any intermediate compounds, achieving hardness and Young's modulus of 25 ± 3 GPa and 437 ± 30 GPa, respectively. As the temperature was further raised to 700 °C, the film developed a layered structure consisting of sheet-like granular clusters, which exhibited excellent toughness while retaining a high hardness of 18 ± 1 GPa. Besides, the resistivity of the films was predominantly stimulated by the crystal morphology.