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.

Author: M.Kim†, J.Kim†, H.Kim and J.Kim*Title: High-Throughput Data-Driven Machine Learning Prediction of Thermal Expansion Coefficients of High-Entropy Solid Solution CarbidesJournal: International Journal of Refractory Metals and Hard MaterialsYear: 2024Impact factor: 3.6Abstract:Recent advances in machine learning and the expanding availability of materials data have enabled significant developments in materials science. In this study, novel configurations of high-entropy ceramic (HEC) materials were explored by predicting their coefficient of thermal expansion (CTE) using machine learning (ML) and high-throughput screening. A machine learning model was built using 3360 datasets containing the thermodynamic, elastic, and thermophysical properties of HEC with carbide configurations of (Ti0.2Ta0.2 × 0.2Y0.2Z0.2)C. The high correlation of the bulk and Young's moduli, and cohesive energy features with the CTE facilitated its prediction. The random forest (RF) and neural network (NET)-based models successfully reproduced the CTE reported in existing experimental and theoretical studies. Overall, first-principles calculation was implemented to configure a database for HEC and a new ML application method is proposed.

2024학년도 2학기 학·석사연계과정 지원 및 선발을 아래와 같이 진행하고자 하니 관심있는 학사과정생들이 지원할 수 있도록 안내하여 주시기 바랍니다.  1. 지원기간 : 2024.06.03(월)~06.14(금)2. 모집학과 : 학사과정과 석사과정에 동일(또는 유사)학과가 있는 학과(계약학과 제외)3. 지원자격 : 다음 각호 모두 해당되는 자가. 지원일 당시 학사과정 4학기 이상 6학기 이내 재학 중(건축학부 건축학전공은 6학기 이상 8학기 이내 재학 중)인 자(학·석사연계과정 신청자는 조기졸업 신청을 할 수 없음)나. 재수강 이전 과목, 학점포기한 과목, F학점 과목 등을 포함한 전체 과목의총평점평균이 3.0 / 4.5 이상인 자다. 7학기 또는 8학기(건축학부 건축학 전공은 9학기 또는 10학기)에 학사과정의 졸업요건을 충족할 수 있는 자라. 지원하고자 하는 일반대학원 학과 주임교수와 지도교수의 추천을 받은 자마. 지원하고자 하는 일반대학원의 동일(또는 유사)학과를 주전공 또는 복수전공으로 하는자4. 제출서류 및 지원방법가. 학·석사연계과정 신청서 1부.나. 대학원 교학팀으로 방문 접수(웨스트민스터홀 658호)5. 선발인원 : 석사과정 입학정원의 20%6. 발표일 : 2024.07.26(금) 예정 - 학과 및 개별통지7. 관련안내가. 대상 : 지원가능 대상자 및 학과나. 방법 : 안내문 배포 및 대학원 홈페이지 공지8. 문의처 : 대학원 교학팀(02-820.0258~9 , grad@ssu.ac.kr)  붙임 : 1. 2024-2학·석사연계과정 안내문 1부.2. 학·석사연계과정 신청서 1부. 끝.