5.  In Situ WC-Cemented Carbide-Based Hardmetals by Selective Laser Melting (SLM) Additive Manufacturing (AM): Microstructure Characteristics and Formation Mechanisms

Selective Laser Melting (SLM) of a W–Ni–graphite powder mixture was performed to prepare in situ WC-cemented carbide-based hardmetals parts, using two different types of CO₂ laser and fiber laser. The WC phase was developed via a multi-laminated growth mechanism and it experienced block-shaped triangular—elliptical morphological change on decreasing the linear laser energy density of the applied CO₂ laser. As the fiber laser was used, the in situ formed WC crystals generally had a triangular microstructure. An increase in the applied linear laser energy density, which was realized by increasing laser power or decreasing scan speed, resulted in the coarsening of in situ WC crystals in both side length and thickness. The SLM additive manufactured cemented carbide based hardmetals parts possessed a sufficiently high densification level of 96.3 % and a maximum microhardness of 1870.9 HV_0.1. The dominant metallurgical mechanisms responsible for the variations of microstructural and mechanical properties of SLM-processed hardmetals parts were proposed.