Microstructural characterization of Mo–12Si–8.5B alloy subjected to diffusion annealing treatment

Microstructural evolutions in the solidification and subsequent diffusion annealing treatment of Mo–12Si–8.5B alloys have been studied by using XRD, OM, SEM and TEM. Because the annealing temperature (1900 °C) is in the vicinity of four-phase equilibrium eutectic reaction (1950 °C) point of L = Mo3Si + Mo5SiB2 (T2)+Moss (Mo solid solution), the dendrites and lamellar phase have almost been dissolved. Dislocations, Moss precipitates and subgrain boundary have been observed in the T2 phase while the other phases are not found. In addition, dislocations are from excess vacancy during the annealing treatment and play important roles for the Moss precipitate. The dislocations can serve as the heterogeneous nucleation sites and compose of sub-boundary which refines the grain size to some extent. The results observed in this study can be used as a reference for future work on the relationships between microstructure and mechanical property of the Mo–Si–B alloys.