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- 저자 : Hongchi Zhou (검색결과 3 건)
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Hongchi Zhou,Yaojun Lin,Fei Chen,Qiang Shen 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.3
This paper reports systematic studies on precipitation behavior of a solid-solution treated single-phase Nb-containingCoCrNi-based face-centered-cubic high-entropy alloy, CoCrNi1.5Nb0.2,at a series of aging temperatures of 660–960 °C fordifferent aging times of 1–48 h, and on the effect of precipitation behavior on tensile strength and ductility. Aging at 660 °Cfor 1–48 h produced disc-shaped coherent γ"-(Ni,Co,Cr)3(Nb,Cr) precipitates of nanometric diameter and thickness withthe D022superlattice, offering precipitation strengthening via dislocation shear mechanism. The diameter monotonicallyincreases with increasing aging time, and the thickness increases with increasing aging time from 1 to 18 h but essentiallyremains unchanged with aging time of 18–48 h; the volume fraction of γ" precipitates constantly increases with increasingaging time. Consequently, yield strength (YS) and ultimate tensile strength (UTS) of CoCrNi1.5Nb0.2increase with increasingaging time due to increased volume fraction and dimensions of γ" precipitates. Uniform elongation (UE) of CoCrNi1.5Nb0.2decreases with increasing aging time due to increased strength of CoCrNi1.5Nb0.2and dimensions of γ" precipitates. Aging at760 °C for 1 h yielded dimensions of γ" precipitates similar to, but volume fraction of γ" precipitates lower than, those duringaging at 660 °C for 48 h, leading to lower YS and UTS and higher UE than those in CoCrNi1.5Nb0.2aged at 660 °C for 48 h. Unlike aging at 660 °C for 1–48 h and at 760 °C for 1 h, aging at 860 and 960 °C for 1 h generated semi-coherent lath-shapedε-(Ni,Co,Cr)3(Nb,Cr) precipitates of submicrometric to micrometric length and submicrometric width with the D019structure,changing precipitation strengthening mechanism to Orowan dislocation bypass mechanism. Submicrometric to micrometricε precipitates provide limited precipitation strengthening, only attaining modest YS and UTS. Despite submicrometric tomicrometric length of ε precipitates, CoCrNi1.5Nb0.2still exhibits a relatively high UE due to strength-ductility tradeoff.
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Hongchi Zhou,Qiang Shen,Fei Chen,Yaojun Lin 대한금속ᆞ재료학회 2023 METALS AND MATERIALS International Vol.29 No.2
This paper reports systematic studies on precipitation behavior of a solid-solution treated single-phase Nb-containingCoCrNi-based face-centered-cubic high-entropy alloy, CoCrNi1.5Nb0.2,at a series of aging temperatures of 660–960 °C fordifferent aging times of 1–48 h, and on the effect of precipitation behavior on tensile strength and ductility. Aging at 660 °Cfor 1–48 h produced disc-shaped coherent γ"-(Ni,Co,Cr)3(Nb,Cr) precipitates of nanometric diameter and thickness withthe D022superlattice, offering precipitation strengthening via dislocation shear mechanism. The diameter monotonicallyincreases with increasing aging time, and the thickness increases with increasing aging time from 1 to 18 h but essentiallyremains unchanged with aging time of 18–48 h; the volume fraction of γ" precipitates constantly increases with increasingaging time. Consequently, yield strength (YS) and ultimate tensile strength (UTS) of CoCrNi1.5Nb0.2increase with increasingaging time due to increased volume fraction and dimensions of γ" precipitates. Uniform elongation (UE) of CoCrNi1.5Nb0.2decreases with increasing aging time due to increased strength of CoCrNi1.5Nb0.2and dimensions of γ" precipitates. Aging at760 °C for 1 h yielded dimensions of γ" precipitates similar to, but volume fraction of γ" precipitates lower than, those duringaging at 660 °C for 48 h, leading to lower YS and UTS and higher UE than those in CoCrNi1.5Nb0.2aged at 660 °C for 48 h. Unlike aging at 660 °C for 1–48 h and at 760 °C for 1 h, aging at 860 and 960 °C for 1 h generated semi-coherent lath-shapedε-(Ni,Co,Cr)3(Nb,Cr) precipitates of submicrometric to micrometric length and submicrometric width with the D019structure,changing precipitation strengthening mechanism to Orowan dislocation bypass mechanism. Submicrometric to micrometricε precipitates provide limited precipitation strengthening, only attaining modest YS and UTS. Despite submicrometric tomicrometric length of ε precipitates, CoCrNi1.5Nb0.2still exhibits a relatively high UE due to strength-ductility tradeoff.
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Synthesis Backbone-Dual-Responsive of Hyperbranched Poly(bis(N,N-ethyl acrylamide))s By RAFT
Yonggang Wu,Libin Bai,Guang Li,Wenliang Li,Sujuan Wang,Xinwu Ba,Guoqiang Zhou,Hongchi Zhao 한국고분자학회 2014 Macromolecular Research Vol.22 No.11
Hyperbranched poly(bis(N,N-ethyl acrylamide))s (HPNAMs) with many vinyls as terminal groups weresynthesized successfully using reversible addition fragmentation chain transfer polymerization (RAFT). Detailedanalyses, based on the molecular weight, α value, degree of branching (DB), and lower critical solution temperature (LCST)obtained from nuclear magnetic resonance (NMR), multi detector-size exclusion chromatography (MDSEC), ultravioletvisible(UV-vis) spectroscopy, and dynamic light scattering (DLS), indicate that we acquired backbone-temperatureand pH responsive HPNAM. Factors, such as DB, molecular weight, and pH value, that affect the LCST were investigated. It was found that the molecular weights of the hyperbranched polymers show significant influence on the LCSTs. For the HPNAMs with low molecular weight, the LCSTs decreased as the DB increased, and the LCSTs can also beadjusted by changing the pH value of solutions. Furthermore, the result of cell cytotoxicity indicates that this new dualresponsive hyperbranched polymer has low cytotoxicity and exhibits potential for biomedical applications.
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