Phase Stability, Micromechanical Behavior, and Low-Temperature Tensile Properties in Ferrous Medium Entropy Alloys

DoctorWith recent advances in the aerospace, marine shipbuilding, and natural gas industries, the demand for metallic alloys having desirable strength and ductility in cryogenic environments has been increased. High-entropy alloys (HEAs) are a newly emerging class of materials that show attractive mechanical properties for structural applications. Particularly, face-centered cubic (FCC) structured HEAs and medium-entropy alloys (MEAs) such as FeMnCoNiCr and CoNiCr alloys, respectively, which exhibit superior fracture toughness and tensile properties at liquid nitrogen temperature, are the potential HEA materials available for cryogenic applications. The underlying strengthening mechanism of these materials is associated with deformation twinning. In the HEA research areas, on the other hand, little research has been conducted on the utilization of metastability-engineering at cryogenic temperatures, and the FCC to body-centered cubic (BCC) martensitic transformation in HEAs. Firstly, in the present thesis, novel ferrous MEAs (FMEAs) exhibiting sequential operation of deformation-induced phase transformation from parent FCC to newly formed BCC phases at low temperatures was developed, and low-temperature tensile properties were evaluated. Detailed deformation responses in relation with microstructural evolution were investigated by electron backscatter diffraction (EBSD) and transmission electron microscopy, combined with in-situ neutron diffraction (ND) analysis. The micro-process analysis qualitatively revealed the correlation between microstructure evolution and the mechanical responses at low temperatures. Secondly, phase stress evolution of the FCC and deformation-induced BCC martensite phases was measured in FMEAs. This was done during tensile deformation at −137 °C using in-situ ND measurements for the quantitative interpretation of the role of martensitic transformation on the improved lowtemperature tensile properties. Thirdly, an integrated experimental-numerical analysis on FMEA was conducted to understand the micromechanical response of the constituent phases. The deformation-induced microstructure evolution related to the phase transformation mechanism and strain partitioning behavior was analyzed using ex-situ EBSD. The mechanical responses related to the stress partitioning between constituent phases and deformation-induced transformation rate were determined using in-situ ND in combination with the nanoindentation analysis. The three-dimensional microstructure volume elements based crystal plasticity models were built based on the experimental results, and the simulations were conducted to quantitatively investigate the stress-strain partitioning behavior

Pannexin 3 is required for normal progression of skeletal development in vertebrates

The vertebrate skeletal system has various functions, including support, movement, protection, and the production of blood cells. The development of cartilage and bones, the core components of the skeletal system, is mediated by systematic inter- and intracellular communication among multiple signaling pathways in differentiating progenitors and the surrounding tissues. Recently, Pannexin (Panx) 3 has been shown to play important roles in bone development in vitro by mediating multiple signaling pathways, although its roles in vivo have not been explored. In this study, we generated and analyzed Panx3 knockout mice and examined the skeletal phenotypes of panx3 morphant zebrafish. Panx3(-/-) embryos exhibited delays in hypertrophic chondrocyte differentiation and osteoblast differentiation as well as the initiation of mineralization, resulting in shortened long bones in adulthood. The abnormal progression of hypertrophic chondrogenesis appeared to be associated with the sustained proliferation of chondrocytes, which resulted from increased intracellular cAMP levels. Similarly, osteoblast differentiation and mineralization were delayed in panx3 morphant zebrafish. Taken together, our results provide evidence of the crucial roles of Panx3 in vertebrate skeletal development in vivo.restrictio

비등원자조성 FeCoNiCr 중엔드로픠 합금: 상온 및 극저온에서의 인장 및 변형 거동

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Grain boundary segregation of boron in FeMnCrCoNi high-entropy alloy

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Phase Transformation and Deformation Behavior of Ferrous Medium-entropy Alloys at Cryogenic Temperature

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Effect of initial grain size on deformation mechanism during high-pressure torsion in VCrMnFeCoNi high entropy alloy

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극저온 강소성 가공을 받은 CoCrFeMnNi 고엔트로피 합금의 미세조직 및 기계적 특성 변화

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A strategy for designing heterogeneous medium-entropy alloys with excellent tensile properties

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CoCrFeMnNi 고엔트로피합금의 이방성 및 디프드로잉 거동 연구

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Annealing Effect on the Mechanical Properties of Hot-Rolled Fe55Co17.5Ni10Cr12.5Mo5 High-Entropy Alloy

Although the mechanical properties of high-entropy alloys depend on the annealing conditions, limited works were established to investigate the annealing effect on the mechanical properties of Mo-added high-entropy alloys. Therefore, in the present work, the annealing effects on the microstructural evolution and mechanical properties of Mo-added high-entropy alloy were investigated. As a result, incomplete recrystallization from the limited annealing time not only suppresses deformation-induced phase transformation during cryogenic tensile test but also induces a deformation instability that results into the ductility reduction compare with the fully recrystallized sample. This result represents adjustment of annealing time is useful to control both transformation-induce plasticity and deformation instability of high-entropy alloys, and this can be applied to control the mechanical properties of metallic alloys by combining pre-straining and subsequent annealing.22Nkc