The low-temperature sinterability of TiO₂-CuO systems was investigated using a solid solution of SnO₂. Sample powders were prepared through conventional ball milling of mixed raw powders. With the SnO₂ content, the compositions of the samples were Ti_1-xSn_xO₂-CuO(2 wt.%) in the range of x ≤ 0.08. Compared with the samples without SnO₂ addition, the densification was enhanced when the samples were sintered at 900°C. The dominant mass transport mechanism seemed to be grain-boundary diffusion during heat treatment at 900°C, where active grain-boundary diffusion was responsible for the improved densification. The rapid grain growth featured by activated sintering was also obstructed with the addition of SnO₂. This suggested that both CuO as an activator and SnO₂ dopant synergistically reduced the sintering temperature of TiO₂.

The green body of WC-Co cemented carbides containing polymeric binders such as paraffin, polyethylene glycol (PEG), and polyvinyl acetate (PVA) are prepared. The green density of the WC-Co cemented carbides increases with the addition of binders, with the exception of PVA, which is known to be a polar polymeric substance. The green strength of the WC-Co cemented carbides improves with the addition of paraffin and a mixture of PEG400 and PEG4000. In contrast, the green strength of the WC-Co does not increase when PEG400 and PEG4000 is added individually. The compressive strength of the green body increases to 14 MPa, and the machinability of the green body improves when more than 4–6 wt% paraffin and a mixture of PEG400 and PEG4000 is used. Simultaneously, the sintered density of WC-Co is as high as 99% relative density, similar to a low binder addition of 1–2 wt%.

Ti_0.5Al_0.5N/CrN nano-multilayers, which are known to exhibit excellent wear resistances, were prepared using the unbalanced magnetron sputter for various periods of 2–7 nm. Ti_0.5Al_0.5N and CrN comprised a cubic structure in a single layer with different lattice parameters; however, Ti_0.5Al_0.5N/CrN exhibited a cubic structure with the same lattice parameters that formed the superlattice in the nano-multilayers. The Ti_0.5Al_0.5/CrN multilayer with a period of 5.0 nm exceeded the hardness of the Ti_0.5Al_0.5N/CrN single layer, attaining a value of 36 GPa. According to the low-angle X-ray diffraction, the Ti_0.5Al_0.5N/CrN multilayer maintained its as-coated structure up to 700°C and exhibited a hardness of 32 GPa. The thickness of the oxidation layer of the Ti_0.5Al_0.5N/CrN multilayered coating was less than 25% of that of the single layers. Thus, the Ti_0.5Al_0.5N/CrN multilayered coating was superior in terms of hardness and oxidation resistance as compared to its constituent single layers.

Nanoparticles of PbTe are prepared via chemical reaction of the equimolar aqueous solutions of Pb(CH₃COO)₂ and Te at 120°C. The size of the obtained particles is 100 nm after calcination in a hydrogen atmosphere. Dense specimens for the thermoelectric characterization are produced by spark plasma sintering of prepared powders at 400°C to 500°C under 80 MPa for 5 min. The relative densities of the prepared specimens reach approximately 97% and are identified as cubic based on X-ray diffraction analyses. The thermoelectric properties are evaluated between 100°C and 300°C via electrical conductivity, Seebeck coefficient, and thermal conductivity. Compared with PbTe ingot, the reduction of the thermal conductivities by more than 30% is verified via phonon scattering at the grain boundaries, which thus contributes to the increase in the figure of merit.

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  Korean Journal of Metals and Materials.2023; 61(6): 422.     CrossRef
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A high temperature dilatometer attached to a graphite furnace is built and used to study the sintering behavior of B₄C. Pristine and carbon doped B₄C compacts are sintered at various soaking temperatures and their shrinkage profiles are detected simultaneously using the dilatometer. Carbon additions enhance the sinterability of B₄C with sintering to more than 97% of the theoretical density, while pristine B₄C compacts could not be sintered above 91% due to particle coarsening. The shrinkage profiles of B₄C reveal that the effect of carbon on the sinterability of B₄C can be seen mostly below 1950°C. The high temperature dilatometer delivers very useful information which is impossible to obtain with conventional furnaces.

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• Application of rate-controlled sintering into the study of sintering behavior of boron carbide
  Hyukjae Lee
  Journal of the Korean Crystal Growth and Crystal Technology.2015; 25(1): 6.     CrossRef

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• Investigation into the microstructure and cutting performance of (Ti,Ta,W)(CN)–Co/Ni cermets
  Se-Woong Oh, Sun-Yong Ahn, Kyung-Sik Oh, Hyukjae Lee, Tai-Joo Chung
  International Journal of Refractory Metals and Hard Materials.2015; 53: 36.     CrossRef

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• Direct Observation on the Low Temperature Degradation Due to Surface Treatment in Y-TZP
  Tai-Joo Chung, Hye-Sung Kim
  Journal of Korean Powder Metallurgy Institute.2010; 17(3): 197.     CrossRef