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Mingya Zhang,Li Liu,Shan Liang,Jinghui Li 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.10
Considering the great advantage of improving the pressing speed in reducing the number of repeated deformation passes andgrain size, high-speed equal channel angular pressing (ECAP) technology has been applied to achieve the perfect distributionof grain size in a sample volume of pure copper. The microstructures and mechanical properties of pure copper sufferingECAP are investigated. The results show that the well refined grains are obtained through three stages, during which the grainreorientation and recrystallization occurs. After ECAP, the volume fraction of high-angle grain boundaries is reduced, butshows an obvious increase in the population for high-pass extruded sample. Besides, ECAP can significantly increase theproportion of the special boundaries probably through the transformation from annealing twins to deformation twins. Thetensile strength of ECAP-ed sample greatly increased to 1.87 times larger than that of the annealed bar, and then improvedslowly regardless of increasing strain. The relationship between strength and grain size still obeyed Hall–Petch formula. The cloud maps of microhardness distribution illustrated that the hardness is severely improved after the first three passes,but leveled off after that. Besides, the cloud maps also present the moderate inhomogeneity of microhardness with highervalues in the edge and lower values towards the center.
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Application of the French Codes to the Pressurized Thermal Shocks Assessment
Mingya Chen,Guian Qian,Jinhua Shi,Rongshan Wang,Weiwei Yu,Feng Lu,Guodong Zhang,Fei Xue,Zhilin Chen 한국원자력학회 2016 Nuclear Engineering and Technology Vol.48 No.6
The integrity of a reactor pressure vessel (RPV) related to pressurized thermal shocks (PTSs)has been extensively studied. This paper introduces an integrity assessment of an RPVsubjected to a PTS transient based on the French codes. In the USA, the “screening criterion”for maximum allowable embrittlement of RPV material is developed based on theprobabilistic fracture mechanics. However, in the French RCC-M and RSE-M codes, whichare developed based on the deterministic fracture mechanics, there is no “screening criterion”. In this paper, the methodology in the RCC-M and RSE-M codes, which are used forPTS analysis, are firstly discussed. The bases of the French codes are compared with ASMEand FAVOR codes. A case study is also presented. The results show that the method in theRCC-M code that accounts for the influence of cladding on the stress intensity factor (SIF)may be nonconservative. The SIF almost doubles if the weld residual stress is considered. The approaches included in the codes differ in many aspects, which may result in significantdifferences in the assessment results. Therefore, homogenization of the codes inthe long time operation of nuclear power plants is needed.
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Jintong Chen,Rui Sun,Guisheng Li,Ming Fang,Gaoshan Xu,Mingya Zhang,Jinghui Li 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.11
The influence of changes in temperature from 250 to 400 °C with 50 °C intervals during ECAP processing on the textureevolution and recrystallization behavior for Mg–9Al–1Zn alloy was studied. The results demonstrate that {10 1 2} extensiontwins and dislocation slip are the dominating deformation modes in low temperature (250 °C and 300 °C) ECAP processing,and those twins gradually disappear with increasing temperature. Most of the recrystallized grains are observed to exhibit(0001) poles 70°–90° away from the normal direction due to reorientation of the grains caused by twins and dislocationslips, with the texture changing from a strong basal texture to the texture component close to { 1 2 1 0} and {01 1 0}. Theproduction of ultrafine recrystallized grains in the specimens treated by ECAP at 400 °C was aided by grain fragmentationcaused by twins interaction, as well as dislocation slip and temperature increase during severe plastic deformation (SPD).
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