synthesis and Characterization of an Alumina Forming Nanolaminated Boride: MoAlB

The MAlB phases are nanolaminated, ternary transition metal borides that consist of a transition metal boride sublattice interleaved by aluminum layers. This study aims to synthesize and characterize MoAlB, a compound within this class of materials, using a reactive hot pressing method. Dense, predominantly single-phase samples were successfully synthesized, and high-resolution scanning transmission electron microscopy confirmed the interleaving of two aluminum layers with a Mo-B sublattice. Remarkably, MoAlB forms a dense amorphous alumina scale upon heating in air, exhibiting oxidation kinetics that follow a cubic time-dependence. The compound showed low resistivity at room temperature (0.36–0.49 µΩm) and demonstrated linear conductivity behavior with decreasing temperatures. It was also characterized as a good thermal conductor (35 Wm−1K−1 at 26 °C) and displayed a thermal expansion coefficient of 9.5 × 10−6 K−1 in the temperature range of 25–1300 °C. Stability tests indicated that MoAlB is stable to at least 1400 °C in inert atmospheres, while its Vickers hardness of 10.6 ± 0.3 GPa and compressive strengths of up to 1940 ± 103 MPa at room temperature suggest promising mechanical properties. These findings promote further investigation of MoAlB for high-temperature applications.