Characterization of Mo-Si-B nanocomposite powders produced using mechanical alloying and powder heat treatment

Mo-Si-B nanocomposite powders with a composition of Mo-12Si-8.5B (in at.%) were processed using mechanical alloying under milling conditions for different milling time and powder-to-ball ratios. The Mo-12Si-8.5B alloy, which consists of α-Mo and intermetallic Mo₃Si and T2 phases, was also synthesized by hot-pressed sintering the mechanically alloyed powders under a pressure of 50 MPa at 1600 °C. The results demonstrated that the sizes and morphologies of the powder particles became gradually refined and uniform by both increasing the milling time and decreasing the powder-to-ball ratio. After 15 h of milling, the powders were completely homogenized at the 1:10 and the 1:15 powder-to-ball weight ratios, and the homogenization was accelerated to rapidly stabilize the milling process because of their high milling energy. Annealing the Mo-Si-B milled powders could promote the growth of the intermetallic Mo₃Si and the T2 phases, which formed even after low-temperature annealing at 900 °C. Increasing the annealing temperature only improved the crystallinity of various phases. When the milled and annealed powders were hot-pressed sintered, the Mo-Si-B alloy exhibited a fine-grained microstructure, where the intermetallics Mo₃Si and T2 were distributed in a continuous α-Mo matrix.