Effects of Laser Surface Re-Melting on the Microstructure and Hardness of Laser Deposited Co-285+WC Coatings
G. Sun, Y. Zhang and C. Liu
A laser deposited Co-285+WC coating on a 1018 mild steel substrate was re-melted using a CO2 laser. Microstructure, composition and microhardness distribution throughout the cross-section of the samples were analysed using scanning electron microscopy (SEM), X-ray spectrometry (EDX), X-ray diffraction (XRD) and microhardness testing. Results indicate that more WC particles dissolved into the CO2 laser re-melted layer, which had a more uniform structure compared with the as-deposited coating. The coral-structured CO2 laser re-melted layer was fine and uniform, differentiating itself from the as-deposited coating which had a dendritic structure with certain various shaped third phases. There was a sharp increase of W content and a sharp decrease of Co, Cr and Ni contents in the re-melted layer close to the interface between it and the as-deposited coating. Element distribution in the CO2 laser re-melted layer was uniform. The microhardness of the CO2 laser re-melted layer was 936 HV0.5, while that of the as-deposited coating was 770 HV0.5. The re-melting of WC particles, re-distribution of W and C elements and the formation of large area W-rich coralstructured phases contributed to the increase in hardness of the CO2 laser re-melted layer.
Keywords: Steel, Co-285 super alloy, deposition, laser re-melting, microstructure, microhardness