DSpace Community: KAIST Dept. of Materials Science and Engineering
http://hdl.handle.net/10203/18
KAIST Dept. of Materials Science and Engineering2024-03-08T11:47:27ZFe-based high-entropy alloy with excellent mechanical properties enabled by nanosized precipitates and heterogeneous grain distribution
http://hdl.handle.net/10203/317156
Title: Fe-based high-entropy alloy with excellent mechanical properties enabled by nanosized precipitates and heterogeneous grain distribution
Authors: Jung, Heechan; Lee, Sangwon; Kang, Taehyeok; Zargaran, Alireza; Choi, Pyuck-Pa; Sohn, Seok Su
Abstract: High-entropy alloys (HEAs) consisting of CoCrFeNiAlTi systems, with a face-centered cubic (FCC) matrix reinforced by ordered L1 2 precipitates, have demonstrated exceptional strength-ductility combinations. However, the current compositional design of HEAs heavily relies on high Ni and Co contents, compromising the balance between properties and cost. Thus, it is crucial to optimize the cost-performance trade-off by fine-tuning the range of Fe, Co, and Ni, while maintaining excellent strength-ductility com-bination. In this study, we propose a novel Fe-based HEA with nanosized precipitates and a heteroge-neous grain distribution, achieving a strength-ductility combination comparable to state-of-the-art Ni -or Co-based HEAs. The alloy benefits from both precipitation hardening and hetero-deformation-induced strengthening attributed to the heterogeneous grain distribution, resulting in excellent yield strength of 1433 MPa, tensile strength of 1599 MPa, and ductility of 22%. The microstructural evolution and its in-fluence on mechanical properties are unraveled with respect to the observation of precipitate-dislocation interaction and hetero-deformation-induced stress (HDI stress) evaluation. This study suggests that the challenge of balancing properties and cost can be addressed through optimized compositional and microstructural design.2024-05-01T00:00:00ZEnhanced interfacial adhesion of patterned Cu-graphene nanolayered composite
http://hdl.handle.net/10203/316598
Title: Enhanced interfacial adhesion of patterned Cu-graphene nanolayered composite
Authors: Kim, Wonsik; Kim, Sang Min; Han, Seung Min
Abstract: In this study, graphene was physically patterned to allow for Cu-Cu contacts to serve as anchoring points, thereby preventing complete delamination at the interface, and the effect of the inclusion of Cu-Cu contacts on bending fatigue response was evaluated. Direct patterning and roll-based dry transfer process of CVD-grown graphene was used to fabricate patterned Cu-Gr nanolayered composites. Bending fatigue tests were performed to determine the optimal configuration of patterning that can lead to enhanced reliability. The graphene was shown to hinder crack formation and propagation, where the cracks were absorbed at the graphene interface through localized delamination while the patterned area with Cu-Cu contact served as anchoring points to prevent macroscopic delamination. Therefore, the optimized graphene patterning design proposed in this study was shown to provide a good balance in crack absorption at the interface and prevention of global delamination that can significantly enhance the reliability under bending fatigue.2024-03-01T00:00:00ZThe phase decomposition in non-equimolar (ZrHfVNbMoW)Cx complex concentrated carbides via carbon content regulation
http://hdl.handle.net/10203/316878
Title: The phase decomposition in non-equimolar (ZrHfVNbMoW)Cx complex concentrated carbides via carbon content regulation
Authors: Zhang, Wen; Li, Kunxuan; Chen, Lei; Shi, Zhan; Huo, Sijia; Wei, Boxin; Kang, Suk-Joong L.; Wang, Yujin; Zhou, Yu
Abstract: (Zr0.196Hf0.02V0.196Nb0.196Mo0.196W0.196)Cx complex concentrated ceramics (CCC) with variable carbon nonstoichiometry are fabricated by hot-pressing sintering at 2100 degrees C for 1 h. The influence of carbon content on phase decomposition behavior and microstructural evolution is investigated. With the decreasing carbon content, the phase transformation of single-phase solid solution -> discontinuous precipitation -> spinodal decomposition -> single-phase occurs, consistent to the binary phase diagram with miscibility gap. The single-phase solid solution decomposes into (ZrHfNb)C-rich and (VMoW)C-rich phases during the phase separation. For spinodal decomposition, the nodular microstructure is formed with coherent crystal orientation relationship of (ZrHfNb) C-rich phase {011} // (VMoW)C-rich phase {011}. The spinodal decomposition leads to in-situ hardening and toughening effects due to the interface hardening and fine microstructure. The spinodal decomposition into two high entropy phases could potentially be beneficial to tailor properties and demonstrated in a future work.2024-03-01T00:00:00ZTo elucidate the effect of alloying elements for enhanced nitriding of aluminum: A multiscale computational study
http://hdl.handle.net/10203/317468
Title: To elucidate the effect of alloying elements for enhanced nitriding of aluminum: A multiscale computational study
Authors: Choi, Jungwoo; Yoo, Jaeyoung; Kang, Ku; Lee, Hyuck Mo
Abstract: The limitations of aluminum (Al) are discussed in certain industrial applications, owing to its low hardness and wear resistance. To overcome these limitations, surface modification techniques, such as the formation of aluminum nitride (AlN) layers on the Al surface, have been explored. However, conventional surface-nitriding processes have low productivity, and it is essential to develop a cost-effective method to ensure higher nitriding rates. This paper presents the results of a multiscale computational study on the atomic-scale mechanisms involved in gas nitriding processes and the effects of alloying elements on reaction kinetics using density functional theory calculations. This study also provides insights into the thermodynamic stability and kinetics of the process, contributing to the design and optimization of the nitriding process for the formation of AlN on Al surfaces using Thermo-Calc. and microkinetic analyses. This study demonstrates the potential of multiscale computational methods for advancing the understanding of surface modification techniques and their applications for nitriding on the surface of Al and suggests the best alloying element to enhance the nitriding rate.2024-02-01T00:00:00Z