Microstructure and mechanical properties of WC-12Co cemented carbide fabricated by laser powder bed fusion on a WC-20Co cemented carbide substrate

In this study, WC-12Co cemented carbides were prepared by laser powder bed fusion (LPBF) on a WC-20Co substrate. The effects of the scanning speed and the substrate on the microstructure, mechanical properties and wear characteristics of the WC-12Co cemented carbide were investigated. The results showed that an alternating distribution of coarse and fine WC grains is observed in the LPBF-prepared WC-12Co cemented carbides. As the laser scanning speed decreases or the laser energy density increases, the WC phase gradually decomposes, accompanied by the loss of C and the formation of ƞ phases. WC-12Co cemented carbides produced at a lower scanning speed exhibit a higher density of thermal cracks, while those produced at a higher scanning speed have a larger number of pores. As the laser scanning speed increases, the transverse rupture strength (TRS) first increases to a maximum value of 823.13 MPa and then decreases. The variation of TRS is mainly attributed to the evolution of the brittle ƞ-phase and metallurgical defects. For WC-12Co cemented carbides formed at low scanning speeds, the brittle η-phase may fracture and cut through the matrix during the friction process, leading to an increase in coefficient of friction (COF) and wear mass loss. For samples formed at high scanning speeds, the formation and detachment of the shear layer could accelerate the friction process and undermine the wear resistance of the WC-12Co cemented carbide. Therefore, the sample prepared at the scanning speed of 400 mm/s shows the best wear performance.