Mechanical alloying behavior of Mo-Si-B based ultrahigh temperature alloy powders by ball milling

The mechanical alloying (MA) behavior of Mo-12Si-10B-3Zr-0.3Y (atomic fraction) powders mixture during ball milling process at 500 r/min was studied by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The results reveal that Mo₃Si and Mo₅SiB₂ phases located in the three phase (Moss-Mo₃Si-Mo₅SiB₂) region of the Mo-Si-B equilibrium phase diagram have not been synthesized by mechanical alloying of the powders mixture and the ball milling products are only super-saturated Moss (Mo solid solution) powders and dispersing B particles with submicron size. The Moss grain size decreases gradually with increasing milling time and finally approaches a steady-state value of about 47 nm after MA for 30 h. On the other hand, the grain size and internal microstrain of Moss increase with increasing milling time and reach 47 nm and 0.53%, respectively, after MA for 30 h. Moreover, a little α-MoSi₂ has been probably synthesized after ball milling for 2 h as shown by the XRD patterns, however, the diffraction peaks of α-MoSi₂ disappear after MA for 30 h. The ball milling products are composed of composite particles with layered structure after ball milling for 5 h, but these layered composite particles have been broken and equiaxed particles are formed after ball milling for 10 h. The ball milling products are finally composed of round particles about 1 μm in diameter.