Synthesis and characterization of aluminum oxide–boron carbide coatings by air plasma spraying

Aluminum oxide (Al2O3)–boron carbide (B4C) composites have been proposed for use as cutting tools as well as in high temperature applications due to their high hardness and fracture toughness. The air plasma spraying method was used to fabricate the composite coatings of Al2O3 and B4C. Three different Al2O3:B4C composition ratios of 90:10, 80:20, and 70:30 by weight were plasma sprayed on plain carbon steel substrates. The effect of B4C content on microstructure, hardness, porosity and thermal diffusivity of the coatings were studied using scanning electron microscopy (SEM), microhardness testing, X-ray diffraction (XRD), and the flash diffusivity method. The plasma spray parameters were optimized in order to achieve a theoretical density of approximately 90%.