Effect Of Sic, WC On Microstructure And Properties Of Co-based Alloy Coatings By Plasma Transferred Arc Welding

SiC and WC reinforced cobalt-based alloy coatings on the surface of the low carbon steel substrate was deposited by plasma transferred arc welding(PTAW). The mass fraction of SiC and WC is 5%, 10%, 20%. Microstructure and phase composition were characterized by optical microscope(OM), scanning microscopy(SEM), energy dispersion spectroscopy and X-ray diffrraction. The Vickers microhardness, elasticity modulus and wear resistance were tested by microhardness tester, nanoindenter and pin-on-disc wear tester, respectively.The XRD patterns of Co-based alloy coating indicate that the coating is composed of γ-Co, Cr23C6 and a small amount of(Cr,Fe)7C3. Co+SiC and Co+WC composite coatings are mainly composed of γ-Co、Cr23C6、CoCx. The fraction of(Cr, Fe)7C3 are increased with addition of different content of SiC, while SiC phase existed in 20%SiC. The phases of WCx and a small amount of Co3C、W2C and M6 C type carbides appeared in Co+WC composite coatings.The microstructure feature of Co-based alloy coating is composed of γ-Co dendrites surrounded by eutectic. And the microstructure of Co+WC composite coatings is the same with Co-based alloy coating. The microstructure of Co+SiC composite coatings is changed from hypoeutectic to hypereutectic as the distance away from fusion zone.The hardness of SiC composite coatings is much higher than that of WC composite coatings, the average microhardness of SiC composite coatings(HV0.5 874) is 27% higher than WC composite coatings(HV0.5689). The wear resistance of SiC and WC composite coatings are much higher than that of Co-based alloy coating, and SiC composite coatings is higher than WC composite coatings at elevated temperature. The wear resistance of 20%SiC composite coating is higher than 20%WC composite coating at elevated temperature. The results showed that there were organization gradient along the layer depth of 20%SiC composite coating. The microstructure of 20%SiC composite coating varies from eutectic in fusion zone to hypereutectic near the surface. In addition, amount of M7C3 type carbides and high toughness and hardness ratio of the composite coating significantly contribute to higher wear resistance of Co+20%SiC composite coating.The mechanism of the wear are predominantly adhesive at room temperature and adhesive wear and oxidation wear at 600℃.The result shows that the coating with 20% SiC has not only excellent performance but low price.