Cemented carbide is a composite material with WC as the main component and Co as the binder phase. Because Co is associated with resource risks, Ni is a candidate as an alternative material. It is known that the strength of WC-Ni cemented carbide can be increased with the decrease of WC particles size. It was clear that adding Ti(C,N) to Ni ultrafine-grained cemented carbide remarkably inhibited the growth of WC particles due to the Ti(C,N) pinning effect. Additionally, optimizing the carbon content and Cr₃C₂ content made the microstructure of WC-Ti(C,N)-Cr₃C₂-Ni ultrafine-grained cemented carbide more uniform, and the bending strength reached 4.3 GPa. Furthermore, when the defects were observed after the tensile test, it was found that the tensile strength increased as the defect size decreased. This was the same as for WC-Co binder ultrafine-grained cemented carbide. In other words, it was found that further increment in strength can be achieved by making the microstructure of WC-Ni ultrafine-grained cemented carbide more uniform and reducing the defect size. These results suggest that WC-Ni binder ultrafine-grained cemented carbide could replace WC-Co binder ultrafine-grained cemented carbide.

Calculated phase diagram of C-Co-V-W quaternary system was attempted to investigate constitution phases of WC-VC-Co cemented carbide during liquid phase sintering. It was found that VC phase could not exist stably for low addition region of VC over liquidus temperature of Co phase in (VC-20Co)-(WC-20Co) pseudo-binary system. It was considered that the formation of (V,W)C phases was classified into three types depending on the additive amount of VC. For the additive amount of less than solubility limit of VC in solid Co at solidus temperature, (V,W)C phase precipitates on WC/Co interfaces from solid Co on low temperature side during cooling. In the range of additive amount between solubility limit in solid Co at solidus temperature and solubility limit in liquid Co at liquidus temperature, (V,W)C phase crystallizes out of liquid phase in temperature during solidification of Co due to the difference between solubility limit in liquid Co and that in solid Co. Above additive amount of solubility limit in liquid Co at liquidus temperature, (V,W)C phase exists in equilibrium with liquid Co above liquidus temperature. It was concluded that inhibition mechanism of grain growth was to differ at solubility limit of VC in Co liquid phase.

The effect of carbon content gradient in WC-Co cemented carbides on the liquid phase migration (LPM) and the shape distortion during sintering was investigated. Ready to press powders for WC-10 mass%Co cemented carbides with high and low carbon contents were prepared. Then, the bi-layered green compacts of round bars and square plates with high and low carbon contents were fabricated and sintered under various conditions. LPM occurred from the high-carbon side to the low-carbon side, which caused the diameter change in the round bars and the warping in the square plates. The amount of LPM and the shape distortion decreased with increasing sintering temperature and sintering time and they increased with decreasing cooling rate from 1673 K. We concluded that the LPM with the carbon content gradient is caused by the generation of the migration pressure in the solid-liquid Co coexistence zone (Π_SL) on the lower carbon side during cooling after sintering. The mechanism of LPM is the same as that from the higher temperature side to the lower temperature side, which we clarified in the previous studies.

AIP is one of the ion plating methods and widely used as a coating method for cutting tools. It produces a dense film but also generates droplets unavoidably. The droplets often negatively affect performance of cutting tools. HiPIMS is one of the sputtering methods that produces a dense and droplet-free film. However, the method has never been put to practical use in cutting tool applications. This is because HiPIMS has more process parameters than AIP, making it more difficult to control the coating. This study has investigated the effects of HiPIMS parameters on the microstructure and physical properties of the coatings. The longer the pulse duration, the higher the deposition rate, which is industrially advantageous. The high peak power density makes the films cubic, resulting in high hardness and compressive residual stress. An indexable milling tool coated with HiPIMS exhibited 1.1 times longer tool life and higher crater wear resistance than the one coated with AIP. A drill coated with HiPIMS exhibited a than 1.6 times longer tool life and less severe wear and weld marks than the one coated with AIP.