Preparation of fine-grained Mo–12Si–8.5B alloys with improved mechanical properties via a mechanical alloying process

Abstract

Mo–12Si–8.5B alloys were prepared using mechanical alloying (MA) followed by hot pressing. The mechanical alloying (MA) process of elemental powder mixtures was used to synthesize the uniform and supersaturated powders. The microstructure exhibits a continuous and uniform α-Mo matrix in which the spherical Mo3Si and Mo5SiB2 particles are distributed. In a more detailed observation of the microstructure, some nanoscale phases consisting of Mo3Si or Mo5SiB2 also precipitated from the α-Mo matrix, which may involve the dissolving out of some Si and B atoms from the metastable supersaturated α-Mo synthesized by the mechanical alloying process. The MA process not only refined the microstructure of the subsequently sintered alloys by decreasing the grain sizes of both the α-Mo and intermetallics phases but also strengthened the α-Mo matrix by solid solution strengthening and dispersion strengthening. Consequently, the yield strength and flexure strength of the alloy prepared from the mechanically alloyed powders were 1915MPa and 1137MPa, respectively, which were superior to those of the alloy prepared by the mixed powders. The discussion was presented by combining with the fracture morphology.