Author: H.Nam†, J.Choi†, H.Kim, J.Lee* and J.Kim*Title: Combined experimental and computational investigation of precipitation behaviour and mechanical properties in a novel Cu–Ni–Si–Co alloy: effect of solution treatment temperatureJournal: Materials TechnologyYear: 2024Impact factor: 2.9Abstract:Cu alloys are extensively utilized in electronics for heat exchangers, electrical conductors, automotive connectors, and electrical contacts. To meet the demands of miniaturization, these alloys must exhibit enhanced strength and electrical conductivity. We investigated the microstructural and precipitation properties of the Cu–Ni–Si–Co alloy at the solution treatment temperature (1,050°C). We subjected the alloy to cold rolling and ageing. The secondary-phase particles dissolved completely at higher temperatures, increasing the concentrations of the Ni, Si, and Co solutes within the Cu matrix. This enhanced supersaturation facilitated higher precipitation during ageing, resulting in fine (Ni,Co)2Si precipitates with a number density of 12.3 × 1010 cm-2. The alloy was strengthened by the Orowan mechanism and exhibited good electrical conductivity. Moreover, nanoscale (Ni,Co)2Si precipitates were formed. We achieved the highest hardness of 251 hV and an electrical conductivity (EC) of 51% International Annealed Copper Standard (IACS).

Author: H.Kim†, H.Lee†, H.Son, I.Bae, J.Choi and J.Kim*Title: Ab initio calculations of Nb-based MAX phases as bond coats for thermal barrier coatingsJournal: Journal of Materials Research and TechnologyYear: 2024Impact factor: 6.2Abstract:Thermal barrier coatings (TBCs) are essential to the reliable high-temperature operation of gas turbines and engines. They comprise a ceramic top coat (TC), a metallic bond coat (BC), and a superalloy substrate. Metallic BCs are common, but they require a minimal difference in the coefficient of thermal expansion (CTE) between the TC and substrate. Among ceramic materials, MAX phases have high CTE. This study reports our use of ab initio calculations to assess the suitability of MAX phases as TBCs. We model Nb-based MAX phases with 211 and 312 structures that have Al or Si at the A sites and C or N at the X sites. We use the quasi-harmonic approximation to calculate the Young’s moduli and CTEs of the materials with respect to temperature. The Nb2SiN MAX phase appears as the most suitable for use as a BC between various ceramic TCs and an Inconel-718 substrate. It is predicted to be effective in relieving thermal stresses due to its high CTE of 10.882 × 10−⁶ K−1 at 1,273 K. The results indicate that carbide MAX phases with high Young’s modulus and low CTE should be used with caution. They may not accommodate thermal stresses as effectively, potentially leading to material failure or reduced performance. Overall, our study indicates the potential of Nb-based MAX structures for use as BCs.

Author: J.Park†, J.Kim†, S.Lee†, H.Kim†, H.Lim, J.Park, T.Yun, J.Lee, S.Kim, H.Jin, K.Park, H.Kang, H.Kim, H.Jin, J.Kim*, S.Kim* and B.Kim*Title: 2D MoS₂ Helical Liquid Crystalline Fibers for Multifunctional Wearable SensorsJournal: Advanced Fiber MaterialsYear: 2024Impact factor: 17.2Abstract:Fiber-based material systems are emerging as key elements for next-generation wearable devices due to their remarkable advantages, including large mechanical deformability, breathability, and high durability. Recently, greatly improved mechanical stability has been established in functional fiber systems by introducing atomic-thick two-dimensional (2D) materials. Further development of intelligent fibers that can respond to various external stimuli is strongly needed for versatile applications. In this work, helical-shaped semiconductive fibers capable of multifunctional sensing are obtained by wet-spinning MoS2 liquid crystal (LC) dispersions. The mechanical properties of the MoS2 fibers were improved by exploiting high-purity LC dispersions consisting of uniformly-sized MoS2 nanoflakes. Notably, three-dimensional (3D) helical fibers with structural chirality were successfully constructed by controlling the wet-spinning process parameters. The helical fibers exhibited multifunctional sensing characteristics, including (1) photodetection, (2) pH monitoring, (3) gas detection, and (4) 3D strain sensing. 2D materials with semiconducting properties as well as abundant surface reactive sites enable smart multifunctionalities in one-dimensional (1D) and helical fiber geometry, which is potentially useful for diverse applications such as wearable internet of things (IoT) devices and soft robotics.

2024년 10월 22일부터 10월 25일까지 부산 아르파나에서 열린 리싸이클링학회와 부산 벡스코에서 열린 섬유공학회에 참석했습니다.

10월 16일부터 10월 18일에 서울 COEX에서 열린 세라믹학회 추계 학술대회에 참석했습니다.

2024년 9월 18일 ~ 20일 일본 오사카 대학에서 열린 The Japan Institute of Metals and Materials 학회에 참석했습니다.