Al–Si/B4C composite coatings on Al–Si substrate by plasma spray technique

Plasma-sprayed coatings of Al–Si/B4C have been prepared on Al–Si piston alloys for diesel engine motors. The Al–Si/B4C composite powders including 5–25 wt% B4C 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, B4C and Al2O3 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 B4C particles were fully wetted by Al–Si alloy. Also, no reaction products were observed in Al–Si/B4C 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 B4C content, the higher the hardness of coatings because the hardness of B4C is higher than that of Al–Si.