Effect of siliconizing temperature on microstructure and phase constitution of Mo-MoSi2 functionally graded materials

Mo-MoSi2 functionally graded materials were prepared by a liquid phase siliconizing method. The microstructure, phase constitution, cross-section elemental distribution, grains size, and coating thickness of these materials were investigated with scanning electron microscopy (SEM), back scattered electron (BSE), energy dispersive spectroscope (EDS), glow discharge spectrum (GDS) and X-ray diffraction (XRD). The results indicate that the Mo-MoSi2 functionally graded materials have a dense multi-layer structure, mainly composed of surface layer (Si-MoSi2 layer, 1-10 µm), intermediate layer (MoSi2 layer, 22-40 µm), transitional layer (Mo5Si3 and Mo3Si layer, 2-3 µm) and Mo substrate. Moreover, the silicon concentration, grains size, and coating thickness increase gradually with the increasing temperature. The surfaces silicon concentrations are about 68-75 wt%, the average grains sizes of MoSi2 columnar crystals are about 7.1-9.4 µm, and the coating thicknesses are about 28-35 µm.