Compositionally graded SiC dispersed metal matrix composite coating on Al by laser surface engineering

Abstract

The present study concerns development of a hard SiC dispersed composite layer on an Al substrate to improve its wear resistance property. A thin layer of SiC (dispersed in alcohol) is pre-deposited (thickness of 100 µm) on an Al substrate and laser irradiated using a high power continuous wave (CW) CO₂ laser. Irradiation of the pre-deposited Al substrate leads to melting of the substrate with a part of the pre-deposited SiC layer, intermixing and rapid solidification to form the composite layer on the surface. Following laser irradiation, a detailed characterization of the composite layer is undertaken in terms of microstructure, composition and phases. Mechanical properties like microhardness and wear resistance are evaluated in detail. The microstructure of the composite layer consists of a dispersion of partially melted SiC particles in a grain refined Al matrix. SiC particles are partly dissociated into silicon and carbon leading to formation of a low volume fraction of Al₄C₃ phase and free Si redistributed in the Al matrix. The volume fraction of SiC is maximum at the surface and decreases with depth. The microhardness of the surface is improved by two to three times as compared to that of the as-received Al. A significant improvement in wear resistance in the composite surfaced Al is observed as compared to the as-received Al. The pitting corrosion property (in a 3.56 wt.% NaCl solution) is marginally deteriorated by laser composite surfacing.