Phase continuity in high temperature Mo–Si–B alloys: A FIB-Tomography Study

The microstructure of mechanically alloyed Mo–Si–B materials of different compositions has been studied by X-ray diffraction and FIB-tomography. Three different phases were found in all alloys: α-Mo solid solution, T2-phase (Mo5SiB2-type) and A15-phase (Mo3Si). The Mo–6Si–5B and Mo–9Si–8B (at%) alloys reveal a continuous morphology of the α-Mo phase. In Mo–9Si–8B the α-Mo phase is distributed more homogeneously compared to the Mo–6Si–5B alloy. In contrast, Mo–13Si–12B does not possess a continuous α-Mo phase. The consequences for the mechanical properties and oxidation resistance are discussed.

Reconstructed volume of the Mo–9Si–8B alloy, revealing the homogeneous microstructure and the contiguity of α-Mo (yellow). The T2+A15 phases are depicted in blue.Figure optionsDownload as PowerPoint slideResearch highlights
► The microstructure of Mo–9Si–8B was found to be homogeneous and the α-Mo phase is continuous.
► The microstructure of the Mo–6Si–5B alloy is less homogeneous but α-Mo is still continuous.
► The microstructure of the Mo–13Si–12B alloy is very heterogeneous and the α-Mo phase discontinuous.
► Scale, volume fraction and contiguity of the α-Mo phase are decisive for satisfying properties.