Ti(C,N)-based cermets have higher hardness and superior resistance to adhesion compared to cemented carbides and are therefore widely used as cutting tool materials. However, their strength and toughness are lower than those of cemented carbides, making them more susceptible to chipping and fracture during cutting operations. To improve the fracture resistance of cermets, methods such as the addition of a third element like tungsten (W) and optimization of nitrogen content have been employed. Nevertheless, in order to meet the demands of severe cutting conditions in high-efficiency machining, it is essential to further enhance fracture resistance. In response, our company has developed and commercialized a high-strength, ultrafine-grained Ti(C,N)-based cermet by refining the Ti(C,N) particles to improve cutting performance. In this paper, we introduce the property improvements achieved by refining Ti(C,N) particles and the related sintering technology.

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.

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.

Additive manufacturing (AM) has become the subject of attention because it can build parts with structures that cannot be achieved by conventional methods. However, one hindrance that has been pointed out to the widespread use of the laser powder bed fusion (L-PBF) method, a type of AM technology, is its high manufacturing costs. An effective method of reducing these costs is reducing manufacturing times and using inexpensive powder. In this research, specimens were built through the L-PBF method by varying the layer thickness using aluminum alloy (AlSi10Mg) broad powder, which included unused coarse powder. Furthermore, we investigated the effects of the particle size distribution of powders and the layer thickness at the time of manufacturing on the relative density of the as-built specimens. As a result, the relative density of the as-built specimen using broad powder was higher than that of a specimen using the existing powder. Although the fabrication conditions of the high-density specimens were limited if the layer was thick, by increasing the layer thickness from 60 µm (conventional value) to 120 µm and adjusting the fabrication conditions, the building speed was increased by 45% while obtaining high-density specimens.

Long-term leakage current characteristics of ZnO varistors are evaluated current flowing behavior by applying a DC voltage of 70 to 80% of the operation starting voltage (V_1mA) or an AC voltage of 85 to 90% of V_1mA/√2 for 1000 hours in a thermostatic oven at 115°C. However, due to thermal runaway in as-sintered specimens, measurements are conducted after heat treatment at 500-600°C. The Schottky energy barrier model fails to consider the factors that cause thermal runaway or the effect of heat treatment on leakage current suppression. Conversely, the proposed composite barrier model can elucidate the aforementioned phenomena by considering the depletion layer in the “holes” (contact areas between ZnO grains) in the intergranular insulating layer as the dominant factor in the leakage current properties. As a result, it reveals that the composite barrier model is the most consistent with the electrical properties as a conduction mechanism model for ZnO varistors that comprehensively covers non-Ohmic behavior and long-term leakage current characteristics.

WC-Cr₃C₂-Ni cemented carbides with improved corrosion resistance are widely used as sliding components in industrial pumps. Firstly, this report presents research on the mechanical properties, corrosion mechanisms, seawater corrosion, and galvanic corrosion of WC-Cr₃C₂-Ni cemented carbides. Next, it discusses the sliding characteristics of cemented carbides, including the mechanism of sliding crack formation and the improvement of lubrication properties through the dispersion of spherical carbon. This report summarizes the advancements in the applicability of cemented carbides as sliding materials.

In recent years, there has been a growing trend for shorter machining time and a shift to dry cutting without the use of cutting fluids. These are expected to reduce power consumption from the standpoint of reducing environmental impact, as well as improve productivity through more efficient machining conditions. These factors cause the cutting edge to a rise in temperature during cutting, and because inserts are used in harsh environments, higher performance is required than in the past. In response to this trend, various technologies have been developed for inserts. Coated cemented carbide inserts have well-balanced wear resistance and chipping resistance compared with uncoated inserts made of other materials. Ceramic coatings applied to inserts include chemical vapor deposition (CVD) coating and physical vapor deposition (PVD) coating. This paper reports on CVD coating technologies.

Hard coatings are used for wear resistance applications, particularly to improve the performance of cutting tools. These cutting tools are mainly coated with TiAlN, TiSiN, and AlCrN. Especially, high aluminum coating and nano-composite coatings exhibit excellent performance. These coatings can significantly improve machining efficiency due to excellent coating properties. Currently, coating technology has evolved significantly in terms of coating composition and deposition equipment. As a result, coating composition and structure have become more complex, and performance has become more advanced. These technologies are based on fundamental PVD technology and hard coatings. This article reviews fundamental PVD technology and hard coatings and provides an overview of the latest technological trends.

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.

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.

Since the invention of cemented carbide about 100 years ago, it has developed through extensive research in both its fundamental and applied fields. In recent years, the manufacturing industry has demanded higher productivity and efficiency, which requires further improvements in cemented carbides. This study began with the steel cord wire drawing dies, which are categorized as wear-resistant tools. It was found that the interface properties of WC significantly impact on the lifetime of steel cord wire drawing. In the wear of cemented carbide dies for steel cord wire drawing, HIP-processed alloys with TaNbC addition showed excellent performance, and further annealing treatment dramatically improved lifetime by a factor of about five. Moreover, ultrafine cemented carbide with fine particle Ti(C,N) additives, which improved interface properties, was found to have a significant effect on inhibiting the growth of WC grains by pinning WC particle surfaces with fine Ti(C,N) particles. Furthermore, ultrafine cemented carbide with a composite addition of fine Ti(C,N) and Cr₃C₂ achieved world-leading strength, recording an average transverse rupture strength of 4.6 GPa and a maximum strength of 5.0 GPa. Tests with this Ti(C,N)-Cr₃C₂ composite-added ultrafine cemented carbide on actual equipment showed results that outperformed conventional products in all cases.