Microstructural and wear properties of WC-12Co cemented carbide fabricated by direct energy deposition

The microstructural and wear properties of WC-12Co (wt.%) cemented carbide bulk material manufactured by additive manufacturing direct energy deposition (DED) process were investigated and compared to those of WC-12Co coating material fabricated by high-velocity oxygen fuel (HVOF) thermal spray process. The feedstock powder, DED and HVOF materials were analyzed using scanning electron microscopy/energy dispersive x-ray analysis (SEM/EDAX), X-ray diffraction (XRD) and an electron back-scattered diffraction (EBSD) technique. WC and alpha-Co phases were observed in the initial WC-12Co cemented carbide powder feedstock. After the DED process, WC phase growth and M12C phase were identified. However, the amount of M12C phase decreased after the HVOF process. The DED material had relatively higher porosity (BD: 11.58%; PD: 10.23%) as compared with HVOF (porosity: 1.66%). The hardness of the HVOF sample was measured as 1429 +/- 49 HV, which was much higher than that of the DED (BD:1373 +/- 68 HV, SD1: 1352 +/- 62 HV) sample, due to the existence of porosity in the DED sample. A pin-on-disc tribometer was used to measure wear rates and coefficients of friction. The wear-worn surfaces were analyzed using SEM with an energy-dispersive spectrometer. The wear test results indicated that the DED material exhibited a lower wear rate (higher wear resistance) and a lower friction coefficient than those of the HVOF material. The difference in the wear behaviour of the DED and HVOF materials could be explained in terms of differences in WC size, the extent of reaction and decarburization during spraying, and the formation of the high oxide content.