Additive Manufacturing of Novel Cemented Carbides with Self-Lubricating Properties

In this research, WC-17Co and WC-Co-hBN cemented carbides were processed using Selective Laser Sintering (SLS) and heat treated at 400 C, 600 C, 800 C and 1000 C for 3 hours to understand the effect of processing and post-processing heat treatment on the structure and properties of the cemented carbide. Electron microscopy and X-ray diffraction (XRD) analysis revealed that the microstructure of the as-printed WC-17Co specimen was characterized by relatively large poly-angular WC/W2C chips, WC-Co dendritic structures, W-C-Co phase and Co-rich regions. WC-Co-hBN also revealed from the microstructure polyangular WC chips which were smaller in size with no W2C phases present in the sample. During heat treatment between 0 C to 600 C, the large poly-angular chips in both WC-17Co and WC-Co-hBN disintegrated to smaller poly-angular chips as a result of the conversion of the unstable W2C phase to the more stable WC phase and the generation of W-Co-N and Co-W-B phases respectively. Heat treatment above 600 C resulted in the coalescence and growth of relatively large WC phase chips. There was significant increase in hardness of the WC-17Co samples during heat treatment when compared with the as-printed WC-17Co sample, with the sample heat-treated at 600 C being 36% harder than the as-printed sample due to the breakdown of poly-angular WC chips and the increase in volume fraction and spatial distribution of the observed W-C-Co phase regions. The increase in hardness at 600 C was coupled with the highest fracture toughness, representing a 34% increase in fracture toughness, when compared with the as-printed sample. The high fracture toughness is attributed to the evolution of the ductile W6Co6C phase in the sample after heat treatment. Nevertheless, the as-printed sample had approximately 15% higher wear resistance than the sample heat-treated at 600 C. In the WC-Co-hBN, the heat-treated samples had lower hardness values compared to the as-printed WC-Co-hBN sample. However, the hardness values were 3 times higher than the hardness value of the WC-17Co sample. This was attributed to the lower grain sizes in the WC-Co-hBN as compared to the WC-17Co samples. The wear resistance of the WC-Co-hBN samples were much higher than the WC-17Co samples with the highest being on the WC-Co-hBN sample heat treated at 1000 C. It is concluded that post-processing heat treatment of SLS printed WC-17Co alloy at 600 C can be used to improve the structure and mechanical properties of the alloy. And a further improvement of the wear properties and hardness of the material can be done by adding a volume of hBN to the alloy.