Author: J.Kwak†, S.Kyung, H.Kim, J.Lee and J.Kim*Title: Ceramic Material Properties in High-Temperature Environments: Recent Trends in Finite Element Analysis ResearchJournal: CeramistYear: 2024Impact factor: Abstract:The finite element method is commonly utilized for high-temperature ceramics, such as cutting tools, thermal/environmental barrier coatings, and aerospace applications. Cutting performance is influenced by both internal and external factors, including heat transfer, and cutting speed. Friction coefficients and heat transfer issues reveal limitations on cutting tool efficiency, requiring accurate modeling and validation. Although oxide formation and crack failure for barrier coatings are discussed, ceramic materials and geometry must be studied. Extensive research on the nucleation and propagation of micro-crack is needed for next-generation spacecraft component applications by validating the established model based on experimental observation. Modeling and verification research improves ceramic reliability under more stress conditions.

Author: Y.Suh†, M.Kim, H.Kim and J.Kim*Title: Oxidative Breakup of Cemented Carbide Scrap by CuO-flux RoastingJournal: International Journal of Refractory Metals and Hard MaterialsYear: 2024Impact factor: 3.6Abstract:Tungsten carbide‑cobalt (WC-Co) composites are widely used in industry as hardmetals with superior properties and performance; however, these qualities make it difficult to recycle components made of WC-Co at their end-of-life. Herein, we present a one-step CuO-flux roasting process in which a solid-state flux supplies sufficient oxygen for the full oxidation of a hardmetal tool piece when melted. Computational assessments of the Gibbs energy of formation and its tendency to form alloys reveal that CuO is suitable for oxidizing WC cutting tools at high temperatures. After roasting a WC-Co cutting insert covered with CuO powder at 1048 °C, the insert loses its shape and changes into a friable solid oxide mass. As the oxidation reaction is highly exothermic and sustainable, the temperatures of the reactants can exceed the melting points of the oxides produced. Meltable oxide-flux roasting can be applied to the recycling of hardmetals, such as carbides and nitrides.

Author: H.Lee†, H.Kim, J.Kwak, S.Kyung and J.Kim*Title: Mechanical Properties of (Zr1-xMx)B2 and (Hf1-xMx)B2 (M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W) for Diboride Fiber Materials: Ab Initio CalculationsJournal: Textile Science and EngineeringYear: 2024Impact factor:Abstract:Zirconium diboride (ZrB2) and hafnium diboride (HfB2) fibers have not been studied as extensively as metal carbides and nitrides for transition metal solid solutions due to a lack of processing technology. However, their remarkable physical properties make them ideal for high-temperature applications. In this study, we investigated the mechanical properties of solid solution diboride using ab initio calculations. Specifically, we focused on the (Zr1-xMx)B2 and (Hf1-xMx)B2 (M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W) compositions. Our findings revealed that ZrB2 and HfB2 have high Young’s moduli of 524.12 and 551.41 GPa, respectively. Additionally, the solid solutions of (Zr0.25Ti0.75)B2 and (Hf0.25Ti0.75)B2 showed superior shear and Young's modulus. We also compared the mechanical properties of titanium-doped diboride solid solutions with undoped ZrB2 and HfB2 at high temperatures. Our study provides valuable insights into the potential development of diborides as ceramic fibers tailored for hightemperature applications.

Author: S.Eo†, J.Lee†, J.Choi†, H.Son, J.Lee, S.Kim, M.Lee, J.Hwang, J.Kim*, D.Jeon* and S.Moon*Title: Strengthening of carbon nanotube fiber using ecofriendly triblock copolymer and newly designed characterization via low-frequency noiseJournal: CarbonYear: 2024Impact factor: 10.9Abstract:In this study, carbon nanotube fibers (CNTFs) were strengthened by densifying and reorienting CNT bundles using a triblock copolymer (poly(propylene glycol)–block-poly(ethylene glycol)–block-poly(propylene glycol (PPG–PEG–PPG)). This copolymer possesses a unique combination of hydrophilic and hydrophobic molecules, enabling it to easily penetrate and expand the distance between bundles. Through a stretching process after impregnation, the CNTFs induced a structural alignment of the bundles, resulting in high integration of the CNT bundles. The microstructural analysis of the fiber cross-section revealed an increased number of aligned CNTs along the fiber direction, concomitant with a reduction in the bundle-to-bundle distance owing to bundle aggregation. The highly aligned structure showed an average specific tensile strength of 0.536 N/tex and specific elastic modulus of 66.3N/tex, which is an increase of 175 % and 252 %, respectively, compared to the pristine CNTF. The polymer infiltration stretching method effectively aggregated CNT bundles and removed macro voids within the CNTF. Additionally, the densification and alignment of CNTFs were characterized through novel low-frequency noise measurement and analysis. Understanding the nanoscale structure and morphology of CNTFs in nanoscale will provide valuable guidance for building enhanced strengthening strategies.

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