Effect of Spraying Powders Size on the Microstructure, Bonding Strength, and Microhardness of MoSi2 Coating Prepared by Air Plasma Spraying

摘要

Molybdenum disilicide (MoSi2) coatings were deposited on carbon steel by air plasma spraying technology with different feedstock powder sizes (i.e., powder A: -15 + 2.5 mu m, powder B: -30 + 15 mu m, powder C: -54 + 30 mu m, powder D: -74 + 54 mu m and powder E: -106 + 74 mu m). Phase composition and microstructure of coatings were characterized by x-ray diffraction (XRD) and scanning electron microscope. The bonding strength and microhardness of coatings were also evaluated. The XRD results show that there exists mutual transformation between T-MoSi2 and H-MoSi2 phase and part of Mo-rich phases are formed because of oxidization during the spraying process. With the increase of spraying powders size, the content of Mo-rich phases (Mo or Mo5Si3) and molybdenum oxide (MoO3) in coatings decreases, and that of disilicide-rich phase (MoSi2) in coatings increases. The oxidation degree of MoSi2 particle gradually decreases during the spraying process with the increase of spraying powders size. The MoSi2 is the main phase of the as-sprayed coatings when the spraying powders size is beyond 30 mu m. With the increase of spraying powders size, the porosity of the as-sprayed coating increases, and the bonding strength of the coating gradually decreases. The hardness of coatings first increases and then decreases with the increase of spraying powders size.