Al–Si/B 4C composite coatings on Al–Si substrate by plasma spray technique

Abstract

Plasma-sprayed coatings of Al–Si/B 4C have been prepared on Al–Si piston alloys for diesel engine motors. The Al–Si/B 4C composite powders including 5–25 wt% B 4C were prepared by mixing and ball-milling processes. These powders were deposited on Al–Si substrate using an atmospheric plasma spray technique. The coatings have been characterised with respect to phase composition, microstructure, microhardness, bond strength and thermal expansion. It was found that Al, Si, B 4C and Al 2O 3 phases were determined in the coatings with approximately 600 μm thick by using X-ray diffraction analysis. Scanning electron microscope observation revealed that boron carbide particles were uniformly distributed in composite coatings and B 4C particles were fully wetted by Al–Si alloy. Also, no reaction products were observed in Al–Si/B 4C composite coatings. It was found that surface roughness, porosity, bond strength and thermal expansion coefficient of composite coatings decreased with increasing fraction of the boron carbide particle. It was demonstrated that the higher the B 4C content, the higher the hardness of coatings because the hardness of B 4C is higher than that of Al–Si.