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RISS 인기검색어
- 검색키워드
- 저자 : M. Rezayat (검색결과 2 건)
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Theoretical Model for Evaluating the Threshold Reduction in Roll Bonding of Al/Al2O3/Al Laminations
M. Rezayat,A. Akbarzadeh 대한금속·재료학회 2012 METALS AND MATERIALS International Vol.18 No.5
Roll bonding is the most important stage of the accumulative roll bonding process, which is used to produce high strength composites. The presence of a particle layer at the interface alters the bonding condition and increases the threshold reduction for the commencement of bonding. In this study, the bonding mechanism in presence of powder at the interface is analyzed and a theoretical model is proposed to predict the required threshold reduction in warm roll bonding of commercially pure aluminum sheets as a function of amount of alumina particles at the interface. The model considers the rolling parameters and the effect of amount and size of particles by defining some constants, which are obtained by experiment. It is shown that the measured values of the threshold reduction are very well predicted by the modeling results.
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Grain Refinement of CoNiCrMo Non-equiatomic Medium Entropy Alloy
M. Rezayat,F. Najib 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.1
Using a thermal–mechanical process, the average grain size of Co35Ni34Cr24Mo7medium entropy alloy was reduced to 2 μm,resulted in 50% improvement of hardness. In this way, the kinetic of the recrystallization and grain growth were investigatedby annealing at the temperature range of 800–950 °C. Based on Differential Scanning Calorimetry analysis and microstructuralinvestigations, recrystallization began around 800 °C at prior grain boundaries, micro shear bands, and intersecteddeformation marking. Comparing Johnson–Mehl–Avrami–Kolmogorov and Austin-Ricket approaches for recrystallizationmodeling the, revealed that the latter is more accurate considering its basic theory, which involves reducing recrystallizationrate by impingement. Both recrystallization and grain growth activation energy were calculated around 380 kJ/mol, which isclose to the activation energy of self-diffusion of similar high/medium entropy alloys. The recrystallization and grain growthtime exponent were found to be less than 0.5, which indicates the heterogeneous deformation and recrystallization in structureand pining effect of Mo on the grain boundaries migration. It was observed that the annealed microstructure containsannealing twins, which their number and thickness are related to the recrystallized grain size. Moreover, it was revealed thatdue to the presence of annealing twins, the modified Hall–Petch equation with effective grain size is more appropriate toexplain the relation of grain size and hardness.
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