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.

In this paper, we focused on Li_1.3Nb_0.3Fe_0.4O₂ with a disordered rocksalt structure as positive-electrode materials for lithium-ion batteries, and investigated an effect of ball milling on the atomic configuration. X-ray absorption fine structure measurements and neutron and X-ray total scattering measurements were performed on an as-synthesized sample (a pristine sample) and a ball-milled sample, and it is revealed that the ball milling disrupts the atomic configuration significantly. In addition, reverse Monte Carlo modeling using the total scattering data was conducted for both the samples, and the obtained three-dimensional atomic configurations were used to visualize the space available for Li⁺ diffusion in charging and discharging processes. The results indicate that the ball milling distorts the Li⁺ diffusion path and causes fragmentation of the path, leading to a deterioration in electrode performance.

The effect of Al addition on the pressure sintering (so-called spark plasma sintering, SPS) behavior of B₄C powder by transient liquid phase sintering (TLPS) was investigated. First, an accurate sample temperature evaluation in a closed graphite die was performed using elemental standard powders. It was found that as the sintering temperature increased, the measurable die surface temperature exponentially decreased compared to the die internal temperature (i.e., sample temperature) due to thermal radiation. Next, pressure sintering treatment of the mixed powder of B₄C containing 5 vol.% Al was performed in vacuum at a constant compressive stress (50 MPa) and heating rate (2 K/s). Although densification due to Al melting was not observed at 933 K, it was found that densification began at temperatures above 1550 K, where the wettability of Al for B₄C is improved, and reached the final stage of sintering at approximately 2200 K. As a result, the densification temperature of B₄C with Al addition could be shifted to a lower temperature by approximately 250 K compared to B₄C without additives. It was suggested that the formation of Al₃BC₃ between Al and B₄C promoted the rearrangement and shape change of B₄C particles, resulting in densification at low temperatures.

In this study, we attempted to fabricate specimens with AlSi10Mg alloy powder by using laser directed energy deposition (DED-LB). Single- and multi-beads (plane) were fabricated with varying DED-LB process conditions, and the bead shapes were measured. Notably, the shapes significantly changed depending on the process conditions. Based on the results, appropriate DED-LB process conditions were selected, under which a smooth plane could be fabricated. Fabricating under the appropriate process conditions, AlSi10Mg DED-LB specimens with a high relative density of greater than 99.8% were obtained. Then, DED-LB specimens with a block shape were fabricated using different scanning patterns (XX and XY patterns) under the appropriate process conditions, and their microstructures and mechanical properties were investigated. The density and microstructural morphology of the DED-LB specimens changed depending on the scanning patterns. The DED-LB specimens fabricated using the XY scanning pattern, in which the scanning direction was changed for each layer, exhibited superior strength and ductility. This was attributed to the differences in relative density and microstructures of the specimens.

Pure magnesium powders added 0.50 g of stearic acid as process control agent (PCA) were mechanically milled (MMed) 24 hours using a vibration ball mill. MMed powders were consolidated into bulk materials by spark plasma sintering (SPS). Changes in hardness, solid-state reactions, bulk density and thickness of the SPS materials have been examined by hardness measurements, an X-ray diffraction, measurements of weight, diameter, height and vernier caliper, respectively. The Vickers hardness of the SPS material decreased with increasing sintering temperature. A minimum hardness value of the SPS material was 19 HV. No effect of sintering pressure on thickness of the SPS materials was observed. Formation of MgH₂ by solid-state reaction during the SPS process was observed for the SPS materials. The sintering temperature contributed to the expansion of the SPS materials than the sintering pressure.

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.