Microstructural and micro-mechanical properties of Mo–Si–B alloyed with Y and La

Nanoindentation and atomic force microscope were used to study the mechanical properties of the individual phases of Mo–9Si–8B–0.2Y and Mo–9Si–8B–0.2La (at%) alloys produced by field assisted sintering. SEM, EBSD, and TEM analysis revealed that the alloys were comprised with the three major phases, molybdenum solid solution (Moss), Mo5SiB2 (T2) and Mo3Si (A15), along with the uniform dispersion of Y or La rich fine-sized precipitates. Both the Y and La-doped Mo–Si–B alloys consisted of fine grain (0.25–0.6 μm) microstructures, and they possessed a superior oxidation resistance compared to the unalloyed Mo–Si–B at higher temperatures. The A15 phase showed the highest hardness and elastic modulus values of the order of 34.9 GPa and 390.4 GPa, respectively for Y-alloyed material. The average modulus values for Moss and T2 phases obtained from these materials were found to be higher than those reported for arc melted Mo–Si–B. The load–displacement curves for T2 and A15 phases showed pop-ins, which could be attributed to the presence of dislocation structures formed as a result of compressive loading during the field assisted sintering process.