Processing and characterization of MoAl1-xSixB solid solutions

The MAB phase MoAlB has attractive properties both at room and high temperatures. To further improve its properties, a possible way is to form solid solutions by partially substituting one of constituting elements in MoAlB. This work reports on the synthesis of MoAl1-xSixB solid solutions by powder metallurgy. Influences of sintering temperature, dwelling time, and composition of starting mixture on the solubility limit of Si in MoAlB have been investigated. The maximum solubility of Si was 0.91 at.%, corresponding to x = 0.03. Increase of Si content in the starting mixtures caused the formation of other competing phases. Phase composition and microstructure were characterized by x-ray diffraction method and scanning electron microscopy. A dense MoAl0·97Si0·03B solid solution has been achieved by hot-pressing a MoB/1.3Al/0.1Si mixture at 1200 °C with 25 MPa for 1 h, and its mechanical properties have been measured. An increase in strength and hardness is achieved by solid-solution strengthening. The flexural strength and the hardness of the solid solution are higher than those of MoAlB, viz. 385 MPa vs 307 MPa, and 14.89 GPa vs 8.43 GPa.