Showing 8 results for Sadeghi
F. Hosseinabadi, A. Rezaee-Bazzaz, M. Mazinani, B. Mohammad Sadeghi,
Volume 17, Issue 1 (March 2020)
Abstract
An experimental–numerical methodology was used in order to study the microstructural effects on stress state dependency of martensitic transformation kinetics in two different TRIP800 low alloy multiphase steels. Representative volume elements extracted from actual microstructure have been utilized for simulating the mechanical behavior of mentioned steels. The mechanical behavior for each constituent phases required in the model has been taken out from those reported in the literature. A stress invariant based transformation kinetics law has been used to predict the martensitic phase transformation during deformation. Crystallographic and thermodynamic theories of martensitic phase transformation have been utilized for estimating the constant parameters of the kinetics law, in a recently performed investigation, but the sensitivity of the transformation to the stress state remained as an adjusting parameter. The results of the current work show that the stress state sensitivity of martensitic phase transformation in the investigated steels is microstructure-dependent and the value of this parameter is almost equal to half of the bainite volume fraction. Therefore, the volume fraction of bainite in the low-alloy multiphase TRIP800 steels can be used as a first postulation for the value of the martensitic phase transformation sensitivity to the stress state and the microstructure based model previously developed for calculating the mechanical behavior of the TRIP800 steels can be utilized as a virtual design tool for development of TRIP steels having specific mechanical properties.
M. Sadeghi, M. Hadi, O. Bayat, H. Karimi,
Volume 17, Issue 1 (March 2020)
Abstract
In this paper a constitutive equation was considered for the isothermal hot compression test of the Mn-Ni-Cr alloy. The hot compression test was performed in the strain rate range of 0.001-0.1 s-1 and deformation temperature was varied from 700 to 900 °C. A considerable reduction in flow stress was observed regardless of the strain rate when temperature was increased from 700 to 750 °C. DTA and XRD evaluation revealed that the removal of Mn3Cr phase and formation of the single solid solution phase were the reason for the flow stress reduction. At the low deformation temperature (700°C) and the high strain rate (0.1 s-1), a partially recrystallized microstructure was observed; this was such that with increasing the temperature and decreasing the strain rate, a recrystallized microstructure was completed. Also, the relationships between flow stress, strain rate and deformation temperature were addressed by the Zener-Holloman parameter in the exponent type with the hot deformation activation energy of 301.07 KJ/mol. Finally, the constitutive equation was proposed for predicting the flow stress at various strain rates and temperatures.
Mitra Ghannadi, Hediye Hosseini, Bagher Mohammad Sadeghi, Bahman Mirzakhani, Mohammad Tahaaha Honaramooz,
Volume 18, Issue 3 (September 2021)
Abstract
The objective of the present paper is to investigate the effects of rapid heating and cryogenic cooling on on the microstructure and tensile properties of Al-Cu-Mg. The specimens were subjected to three heat treatment cycles in which the Infrared heating (IR) were used as the heating medium at the ageing stage, and the liquid nitrogen and water were used as the quenching mediums. The ageing temperature and time were 190⁰C and from 2 hours to 10 hours, respectively.The results indicated that by using IR at the ageing stage, the hardening rate enhanced because the rapid heating via this method leads to faster diffusion of the alloying elements. Moreover, the high density of nano-sized precipitates formed during ageingleads to higher strength and suitable ductility. Cryogenic treatment showed a negligible effect on both microstructure and tensile properties; however, it improved ductility. Overall, the combination of a high heating rate and cryogenic treatment led to the highest mechanical properties. SEM micrograph of the fracture surface of alloy demonstrated that in Cryogenic treatment+Artificial Ageing (CAA) condition, the surface had been fully covered by deep dimples in contrast to the Cryogenic treatment+Infrared Heating (CIR) and Water-Quench+ Infrared Heating (QIR) conditions which their dimples were shallow and also some facets were observed.
Morteza Hadi, Omid Bayat, Hadi Karimi, Mohsen Sadeghi, Taghi Isfahani,
Volume 19, Issue 1 (March 2022)
Abstract
In this research, the effect of initial microstructure and solution treatment on rollability and crystallographic texture of a Cu-Mn-Ni-Sn alloy has been investigated. The initial tests indicated that the rolling of the alloy at different temperature conditions is not possible due to formation of second phases. Herein to eliminate the segregated phases, according to DTA analysis, proper temperature for solution treatment was selected as 750°C applied at different periods of time. The obtained results showed that after 15-hour solution treatment, the complete elimination of Sn, Mn, Ni, and Fe-rich phases can be achieved. Also, the peaks of XRD shifted to the higher angles indicating that the alloying elements are dissolved. Meanwhile, the intensity of the texture reduced and the dominant texture changed from Goss and Brass-texture to Copper-texture. Accordingly, the amount of maximum total reduction at the rolling process increased from 16.37 to 109.46 after solution treatment.
Saba Payrazm, Saeid Baghshahi, Zahra Sadeghian, Amirtaymour Aliabadizadeh,
Volume 19, Issue 3 (September 2022)
Abstract
In this research, zinc oxide quantum dots and graphene nanocomposites were synthesized via two different methods; In the first (direct) method, ZnO-graphene Nanocomposites were made mixing the synthesized zinc oxide and graphene. In the second (indirect) method, zinc nitrate, graphene, and sodium hydroxide were used to made ZnO-graphene Nanocomposites. XRD, FTIR and Raman spectroscopy analyses were used for phase and structural evaluations. The morphology of the nanocomposites w::as char::acterized by SEM. The specific surface area and porosity of the samples were characterized by BET analysis. The optical properties of the samples were investigated by photoluminescence and ultraviolet-visible spectroscopy analyses. Results showed that using graphene, increased the photoluminescence property and shifted the photoluminescence spectrum of the composites towards the visible light spectrum. The photoluminescence of the synthesized graphene-zinc oxide composite, in the visible light region, was closer to white light than that of pure zinc oxide. According to the results of BET test, the nanocomposite synthesized by direct method had a higher surface area (25.7 m2.g-1) and a higher porosity (0.32 cm3.g-1) than the nanocomposite synthesized by the indirect method with a specific surface area of (16.5 m2.g-1) and a porosity of 0.23 cm3.g-1).
