Evaluation of WC-9Co-4Cr laser surface alloyed coatings on stainless steel

Abstract

In order to examine the microstructure and hardness behaviour of WC cermets, coatings have been obtained by laser surface alloying technique. WC-9Co-4Cr particulate was injected onto the surface of AISI 304L austenitic stainless steel (ASS) under different laser processing variables. The morphologies and microstructures of the composite coatings were investigated using optical microscopy and high resolution field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectrometer (EDS), while the phase changed were observed using x-ray diffraction (XRD). The surface hardness was determined using the Vickers microhardness tester. The decomposition of WC-9Co-4Cr into W2C, C and W is as a result of low heat of formation of WC and low affinity of tungsten for Carbon. Free Co and C in the meltpool formed intermetallic phases such as Co6W6C and M23C6 (M=Fe, Cr, W). A considerable increase in hardness value of the matrix 246 Hv0.1 compared to the coating 1331 Hv0.1 was achieved when alloying was carried out at 2.0 kW laser power and scan speed of 0.6 m/min.