CMDL의 박사과정 김효경 학생이 2023년도 한국섬유공학회 학문후속세대 논문상 수상자로 선정되었습니다!수상을 축하드립니다!

Author: H.Kim†, H.Lee, J.Kwak, and J.Kim*Title: Mechanical Properties of (Ti0.875M0.125)N (M=Cr, Hf, Mn, and Zr) Solid Solutions: Investigation of Coating Materials for Fiber-reinforced Ceramic Matrix Composites via ab Initio CalculationsJournal: Textile Science and EngineeringYear: 2023Impact factor:Abstract:Nitride coatings improve the material properties of fiber in fiber-reinforced ceramic matrix composites, and in this study, we investigated the mechanical properties of (Ti0.875M0.125)N using ab initio calculation. We focused on the substitutional effect of a small amount of transition metal M (M=Cr, Hf, Mn, and Zr) in the titanium site. For the reliability of the data, it was set based on the model size and mechanical properties of known undoped ceramics. The shear and Young's modulus were the best in (Ti0.875Hf0.125)N solid solutions. CrN was the best among the whole compositions in bulk modulus, and (Ti0.875Mn0.125)N was the best among solid solutions in bulk modulus. The results of this study will provide useful information on how to develop nitrides as coating materials for fiber-reinforced ceramic matrix composites.

Author: H.Kim†, J.Choi, S.Park, T.Eom, K.M.Roh* and J.Kim*Title: Influence of vacancies on the stability and mechanical properties of V2AlC: Guidelines for etching MAX phases via ab initio calculationsJournal: Ceramics InternationalYear: 2024Impact factor: 5.2Abstract:This study focuses on the ideal etching of defective MAX phases in a mechanical exfoliation process to produce vanadium-based MXenes. Two-dimensional MXenes exhibit high structural stability and excellent electrical conductivity, and can be applied as electrode materials. Mechanical exfoliation can be facilitated by modifying the vacancy in the V2AlC MAX phase, which makes etching challenging. We report the effects of M (vanadium), A (aluminum), and X (carbon) vacancies on the mechanical behavior of V2AlC via ab initio calculations. To this end, the anisotropic mechanical properties and strain–stress curves were calculated for MAX phases with different vacancies (x = 0.08, which corresponds to 8.33 at.%). The presence of vanadium vacancies significantly deteriorated the structural and mechanical properties compared to those of aluminum and carbon vacancies. Thus, it was confirmed that vanadium vacancies had a significant effect on the mechanical exfoliation of the MAX phases. These findings provide further insights into the design of MXenes.

Author: S.Lee†, J.Choi, Y.Chung, J.Kim*, S. Moon* and S.Lee*Title: Understanding the catalytic mechanism of calcium compounds for enhancing crystallinity in carbon fiberJournal: Chemical Engineering JournalYear: 2024Impact factor: 15.1Abstract:Graphitized carbon fibers are attractive materials because of their high tensile modulus and thermal and electrical conductivities. These attributes derive from their crystalline structures that develop during heat treatments of up to 3000 °C. Despite the costly thermal processes, there is a structural limit for achieving these sought-after properties for polyacrylonitrile-based carbon fibers. Herein, the preparation of polyacrylonitrile-based carbon fibers with highly developed microstructures via calcium-assisted thermal treatments of up to 2700 °C is reported. Carbon fibers hydrothermally immersed in a solution of calcium carbonate were heat-treated and their chemical structures traced to investigate the calcium-assisted catalytic graphitization mechanism. Graphitic structures appeared at 1400 °C, accompanied by intermediate complexes of carbon and calcium on the carbon fibers surfaces. Further heat treatment of the calcium compounds at 1600 °C to incorporate carbon fibers resulted in an interlayer spacing of 0.3360 nm, which was unachievable solely through heat treatment at 2700 °C. In addition, the achieved tensile modulus and electrical conductivity of 480 GPa and 1.7 × 103 S/cm, respectively, were significantly higher than those of pure carbon fibers. The calcium ions penetrating the internal structure of the carbon fibers aligned the non-uniform graphene structure and developed the graphite structure of the carbon fibers by acting as catalysts, even at low temperatures.

Author: H.Nam†, H.Lee†, H.Kim, J.Lee* and J.Kim*Title: Precipitation strengthening of Cu–Ni–Si-based alloys: Experimental and computational insightsJournal: Journal of Materials Research and TechnologyYear: 2023Impact factor: 6.4Abstract:The effects of interfacial energy on precipitation behavior and physical properties of Cu–Ni–Si–(Co) alloys were investigated. The Cu–1.3Ni–0.3Si and Cu–1.3Ni–0.6Si–1.0Co alloys (in weight %) were prepared by combined cold-rolling and aging processes. The addition of Co promoted the formation of (Ni,Co)2Si by replacing Ni with Co in Ni2Si. Ab initio calculations demonstrated that the small addition of Co considerably reduced the interfacial energy between the Cu matrix and (Ni,Co)2Si, which effectively decreased the activation energy for precipitation. As a result, the precipitation of fine rod-shaped (Ni,Co)2Si was accelerated during the aging process and the number density of the precipitates increased up to 9.0 × 1010 cm−2. The nano-scale (Ni,Co)2Si precipitates with an average size of 13.5 nm strengthened the alloy properly through the Orowan mechanism without much loss of electrical conductivity. The maximum hardness and electrical conductivity were 220 Hv and 51 % International Annealed Copper Standard, respectively, for the Cu–1.3Ni–0.6Si–1.0Co alloy aged for 4 h at 420 °C.