WITHDRAWN: Effect of heat treatment on microstructural evolution and properties of cemented carbides (WC-17Co) processed by selective laser sintering

Abstract

Abstract Processing materials such as cemented carbides (WC-Co) using metal-based Additive Manufacturing (AM) presents many challenges due to the material and complex mechanisms that occur during processing. Powder composition, processing parameters and post-processing treatments dictate the microstructural integrity and mechanical properties of the processed parts. In this study, WC-17Co cemented carbides were processed using Selective Laser Sintering (SLS) and heat treated at 400 °C, 600 °C, 800 °C and 1000 °C for 3 h to understand the effect of processing and post-processing heat treatment on the structure and properties of the WC-17Co cemented carbide. Electron microscopy and X-ray diffraction (XRD) analysis revealed that the microstructure of the as-printed specimen was characterized by relatively large polygonal WC/W2C chips, WC-Co dendritic structures, WC-Co “foggy” and Co-rich regions. During heat treatment between 0 °C and 600 °C, the large polygonal chips disintegrated to smaller polygonal chips as a result of the conversion of the unstable W2C phase to the more stable WC phase. Heat treatment above 600 °C resulted in the coalescence and growth of relatively large WC phase chips. In addition, globular WC-Co dendritic structures evolved with increase in temperature coupled with a reduction in the volume fraction of the Co-rich regions. There was significant increase in hardness of the samples during heat treatment when compared with the as-printed sample, with the sample heat-treated at 600 °C being 36% harder than the as-printed sample due to the breakdown of polygonal WC chips and the increase in volume fraction and spatial distribution of the observed “foggy” 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. 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.