Synthesis, microstructure and properties of MoAlB ceramics

High purity MoAlB powder was synthesized at 1100 °C starting from MoB and Al powders with a molar ratio of 1–1.6. The excess of Al contributed to achieve a single phase MoAlB during the synthesis. Al excess was subsequently etched out using HCl. Dense MoAlB bulks were consolidated by hot pressing at 1600 °C under 60 MPa resulting in a relative density as high as 96.7%. Extensive analysis of mechanical, thermal and electrical properties is here reported. The electrical conductivity of 2.91 ± 0.23 × 106 S/m, and thermal conductivity of 29.21 ± 0.01 W/m K confirmed a metallic conduction behavior. The flexural strength of 456.4 ± 19.1 MPa, Vickers hardness of 9.3 ± 0.4 GPa, compressive strength of 1620.2 ± 85.6 MPa, and fracture toughness of 4.3 ± 0.1 MPa m1/2 were comparable with other ternary layered compounds (MAX phases). The oxidization resistance was investigated up to 1600 °C where a passivating Al2O3 scale inhibited further oxidation even when heating/cooling the sample for five consecutive cycles.