Microstructural and hardness investigation of a multiphase Mo-Si-B alloy processed by laser surface remelting

In this study, the effect of laser surface remelting on the microstructure and mechanical properties in a hot-pressing sintered Mo-Si-B alloy was investigated. In contrast to equiaxed grains in the base metal (BM), a typical dendritic structure with coarse alpha-Mo dendrite stems and nano-sized interdendritic eutectics (alpha-Mo + T2 + Mo3Si), was obtained in the fusion zone (FZ). Through a coupling of electron backscattered diffraction (EBSD) and nanoindentation techniques, a correlation of phase map and surface topography was achieved, ensuring the unambiguous determination of mechanical properties for individual phases. In this way, reasonable hardness and elastic modulus of individual phases in both the BM and the FZ were attained after correcting the load-depth curves with pop-ins. The absence of pop-in events in the alpha-Mo dendrite in the FZ is mainly due to a high dislocation density associated with the high cooling rate during LSR. Moreover, the FZ exhibits a better indentation fracture toughness (similar to 5.2 MPa.m(1/2)) than the BM (similar to 4.4 MPa.m(1/2)), probably due to the bimodal distribution of alpha-Mo grain size.

Automated summary

The effect of laser surface remelting on the microstructure and mechanical properties in a hot-pressing sintered Mo-Si-B alloy was studied. The fusion zone exhibited a dendritic structure with coarse alpha-Mo dendrite stems and nano-sized interdendritic eutectics. The combination of electron backscattered diffraction and nanoindentation techniques allowed for the determination of mechanical properties of individual phases, showing that the fusion zone had better indentation fracture toughness due to the bimodal distribution of alpha-Mo grain size.