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RISS 인기검색어
- 검색키워드
- 저자 : M. Kazeminezhad (검색결과 3 건)
- 무료
- 기관 내 무료
- 유료
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Post Deformation at Room and Cryogenic Temperature Cooling Media on Severely Deformed 1050-Aluminum
M. Sarkari Khorrami,M. Kazeminezhad 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.2
The annealed 1050-aluminum sheets were initially subjected to the severe plastic deformation through two passes of constrainedgroove pressing (CGP) process. The obtained specimens were post-deformed by friction stir processing at roomand cryogenic temperature cooling media. The microstructure evolutions during mentioned processes in terms of grainstructure, misorientation distribution, and grain orientation spread (GOS) were characterized using electron backscattereddiffraction. The annealed sample contained a large number of “recrystallized” grains and relatively large fraction (78%) ofhigh-angle grain boundaries (HAGBs). When CGP process was applied on the annealed specimen, the elongated grainswith interior substructure were developed, which was responsible for the formation of 80% low-angle grain boundaries. TheGOS map of the severely deformed specimen manifested the formation of 43% “distorted” and 51% “substructured” grains. The post deformation of severely deformed aluminum at room temperature led to the increase in the fraction of HAGBsfrom 20 to 60%. Also, it gave rise to the formation of “recrystallized” grains with the average size of 13 μm, which werecoarser than the grains predicted by Zener–Hollomon parameter. This was attributed to the occurrence of appreciable graingrowth during post deformation. In the case of post deformation at cryogenic temperature cooling medium, the grain sizewas decreased, which was in well agreement with the predicted grain size. The cumulative distribution of misorientationwas the same for both processing routes. Mechanical properties characterizations in terms of nano-indentation and tensiletests revealed that the post deformation process led to the reduction in hardness, yield stress, and ultimate tensile strengthof the severely deformed aluminum.
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Rapid Annealing of Severely Deformed Low Carbon Steel in Subcritical Temperature Range
H. Ghiabakloo,M. Kazeminezhad 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.5
A low-carbon steel sheet containing 0.05 C, 0.203 Mn, and 0.0229 Si (all in wt%) was rapidly annealed in a temperaturerange of 300 °C to 600 °C after severe plastic deformation by using constrained groove pressing (CGP)technique. Microstructure evolution was investigated by scanning electron and optical microscopes. Mechanicalproperties were evaluated by hardness measurements and shear punch test. The results showed a thermal stabilityup to 400 °C where recrystallization did not occur in the specimens even after 7200 s. This thermal stability is inagreement with previously reported results of conventional annealing of the same steel after CGP. However,annealing at 500 °C and 600 °C led to recrystallization which started after holding times of 600 s and 20 s, respectively. Longer holding times resulted to grain growth and deterioration of strength and hardness, but the finalstrength and hardness were still higher than those of conventionally annealed specimens. The reason has beenattributed to no abnormal grain growth in the present study, in contrast to that occurs after conventional annealingof CGPed low carbon steel. The kinetics of recrystallization at 600 °C was studied using the celebrated Johnson-Mehl-Avrami-Kolmogorov (JMAK) model; the results showed a bi-linear JMAK plot indicating two differentstages of recrystallization rate before and after 70% recrystallization.
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Surrogate-based Pareto optimization of annealing parameters for severely deformed steel
Ghiabakloo, H.,Lee, K.,Kazeminezhad, M.,Kang, B.S. Elsevier Ltd 2016 Materials & Design Vol.92 No.-
<P>Severe plastic deformation (SPD) is a metalworking technique that is used for the enhancement of the strength and hardness of metallic materials. As SPD causes ductility deterioration, materials typically necessitate annealing for ductility increase; however, annealing may conversely affect strength and hardness. Thus, to optimally balance strength, hardness, and ductility, this study determined annealing conditions with a severely deformed low carbon steel sheet by adjusting annealing time and temperature. For the facilitation of the annealing process optimization, measurements of strength, hardness, and ductility under various annealing conditions were represented by regression Kriging. Then, because of the conflicting nature of the desired metal properties, a set of optimal annealing conditions was identified by Pareto multi-objective optimization. Finally, the best combination on the Pareto front was selected with TOPSIS. The results of Pareto optimization with regression Kriging showed that the best candidates for annealing conditions can be determined at a significantly reduced experimental cost. (C) 2015 Published by Elsevier Ltd.</P>
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