Grain Growth in Nanocrystalline Iron and Fe-Al Alloys

Hamed Mirzadeh,Amir Zomorodian 대한금속·재료학회 2010 METALS AND MATERIALS International Vol.16 No.1

The effects of the annealing temperature and time, cryomilling in liquid nitrogen, and the addition of aluminum powder on the thermal stability and grain growth behavior of nanocrystalline iron were modeled using the Artificial Neural Network (ANN) technique. The developed model can be used as a guide for the quantification of the grain growth by considering the effects of annealing temperature and time. The model also quantified the effect of Al on the thermal stability of cryomilled nanocrystalline Fe. The model results showed that the cryomilling of Fe has a tangible effect on the stabilization of the nanostructure.

Eff ect of Intercritical Annealing Conditions on Grain Growth Kinetics of Dual Phase Steel

Fateme Najafkhani,Hamed Mirzadeh,Mehran Zamani 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.4

The study of grain coarsening and its kinetics during intercritical annealing is of vital importance for the production of dualphase (DP) steels with appropriate microstructure and properties required for industrial applications. In the present work, thekinetics of grain growth in the two-phase austenite plus ferrite region was studied based on the parabolic grain growth law. It was revealed that the thermally-activated grain growth of ferrite depends on the soaking temperature and the presence ofaustenite islands, where these two factors compete with each other. As a result, by increasing the temperature, initially the rateof growth increases and the activation energy of grain growth ( Q ) was determined as 615 kJ/mol, which indicates the hightemperaturedependency. However, after the formation of a certain amount of austenite and the formation of chain-networkmorphology of austenite, the increase of temperature results in a decreased growth rate with the Q value of − 258 kJ/mol. This suggests that the pinning eff ect counteracts the temperature eff ect in this stage. The eff ect of grain size on mechanicalproperties and work-hardening behavior was also discussed. Higher work-hardening rate was observed for the fi ne-grainedDP microstructures, which was found to be responsible for the better strength–ductility trade off .

Processing Route Effects on the Mechanical and Corrosion Properties of Dual Phase Steel

Maryam Soleimani,Hamed Mirzadeh,Changiz Dehghanian 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.6

The mechanical and corrosion behaviors of low carbon DP steel were studied based on different processing routes: (1)intercritical annealing (IA), (2) step quenching (SQ) via austenitization and quick transferring of the sample to the secondfurnace, and (3) Slow SQ via furnace cooling to the desired temperature. The properties were found to be highly dependenton the volume fraction of martensite (VM) and the density of ferrite/martensite interfaces. However, at the same martensitecontent, the mechanical properties of Slow SQ sheet were inferior than those of SQ and IA sheets, which were related to therelatively poor work-hardening behavior due to the severe partitioning of Mn between ferrite and martensite phases. Thelatter was also responsible for an increase in the corrosion current density (icorr) via galvanic corrosion. These results wereanalyzed based on the polarization curves and Nyquist plots obtained from the electrochemical impedance spectroscopytest. This study revealed that the SQ route can result in both better mechanical performance and higher corrosion resistance.

Modeling the compressive strength of cement mortar nano-composites

Reza Alavi,Hamed Mirzadeh 사단법인 한국계산역학회 2012 Computers and Concrete, An International Journal Vol.10 No.1

Nano-particle-reinforced cement mortars have been the basis of research in recent years and a significant growth is expected in the future. Therefore, optimization and quantification of the effect of processing parameters and mixture ingredients on the performance of cement mortars are quite important. In this work, the effects of nano-silica, water/binder ratio, sand/binder ratio and aging (curing) time on the compressive strength of cement mortars were modeled by means of artificial neural network (ANN). The developed model can be conveniently used as a rough estimate at the stage of mix design in order to produce high quality and economical cement mortars.

Revisiting the Diffusion of Niobium in an As‑Cast Nickel‑Based Superalloy During Annealing at Elevated Temperatures

Mohammad Javad Sohrabi,Hamed Mirzadeh 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.3

While understanding the interdiffusion of Nb in the austenite matrix of Ni-based superalloys is important for studying theprecipitation reactions (Laves phase, γ″-precipitates and δ-phase) and homogenization of the as-cast structure, there is noreport on the activation energy (Q) and pre-exponential factor (D0). Moreover, for the Ni–Nb diffusion couple, the reportedQ values of 202.6 and 257 kJ/mol are not consistent. In the present work, based on the concept of residual segregation indexduring homogenization treatment and elemental analyses from dendrite cores and interdendritic segregated regions, Q andD0 were respectively determined as ~ 236 kJ/mol and 0.0053 cm2/s for the Ni-based superalloys. Improved analysis of theNi–Nb system resulted in Q and D0 values of ~ 234 kJ/mol and 0.1618 cm2/s, respectively. Therefore, it was concluded thatthe activation energy for interdiffusion of Nb in superalloys and Ni–Nb diffusion couple is the same. However, due to thepresence of other alloying elements in the superalloys, D0 for Ni–Nb diffusion couple is ~ 30 times that of the superalloys.

Synergistic Effects of Cerium-Based Rare Earth Addition and Hot Deformation on the Microstructure and Mechanical Properties of Mg-0.5Zn-0.5Zr Magnesium Alloy

Hooman Abedi,Massoud Emamy,Jafar Rassizadehghani,Hamed Mirzadeh 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.5

The effects of cerium-based rare earth (RE) addition and hot deformation via extrusion on the microstructure and mechanicalproperties of Mg-0.5Zn-0.5Zr alloy were studied. It was found that RE addition could effectively refine the as-cast microstructureup to 2 wt% RE with a notable grain refining effect up to 1 wt% RE. High RE additions resulted in a less effectivegrain refinement and the appearance of coarse dendritic microstructure. While the as-cast strength and ductility wereenhanced by increasing RE content up to 1 wt% due to grain refinement, alloys with high RE content faced a remarkable dropin total elongation and also showed lower ultimate tensile strength (UTS) values, which was related to the interconnectedintergranular brittle intermetallics (Mg12RE) with high volume fractions. For the extruded alloy with 1 wt% RE, besidesthe fragmentation and dispersion of intermetallics, a remarkable grain refinement due to the recrystallization processes wasobserved. Accordingly, the UTS of 415 MPa, total elongation of 17% and tensile toughness of 65.9 MJ/m3 were obtained afterextrusion, which are quite superior to the corresponding values of 210 MPa, 12% and 22.1 MJ/m3 for the as-cast counterpart,respectively. Regardless of the processing condition, the grain size effect was found to be the dominant factor in determiningthe yield stress (Hall–Petch law), where the deviation of this trend due to the presence of hard Mg12REphase was discussed.

Effect of Gd on Dynamic Recrystallization Behavior of Magnesium During Hot Compression

Mohammad Hossein Barezban,Reza Roumina,Hamed Mirzadeh,Reza Mahmudi 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5

Dynamic recrystallization (DRX) behavior of two binary Mg–0.5Gd and Mg–1.5Gd alloys and pure Mg were studied by hotcompression in the temperature range of 300–450 °C to explore the role of Gd on DRX grain size refinement and kinetics.The dependency of DRX grain size on the Gd content during hot compression was quantified and expressed based on theZener–Hollomon parameter. While the exponent of the Zener–Hollomon parameter was obtained as − 0.118 independentof the Gd content, the proportionality constant varied by Gd concentration. The developed expression revealed significantreduction in the DRX grain size of the Mg–Gd alloys. The volume fraction of dynamically recrystallized grains was calculatedby applying the Johnson–Mehl–Avrami–Kolmogorov type model, which resolved the faster kinetics for DRX of the Mg–1.5Gd alloy compared to ones for the Mg–0.5Gd alloy and pure Mg. The higher driving pressure for DRX of the Mg–1.5Gdalloy was justified based on dislocation density measurements at the onset of DRX through the Williamson-Hall method.

Thermal Mechanisms of Grain Refinement in Steels: A Review

Zahra Nasiri,Sajad Ghaemifar,Meysam Naghizadeh,Hamed Mirzadeh 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.7

Thermal mechanisms of microstructural refnement in steels were reviewed. These include thermal cycling, martensiteprocess, and static recrystallization (SRX), in which the dominant stage of microstructural refnement is governed by anannealing treatment of a deformed or an undeformed material. Recent progress in grain refnement by thermal cycling forthe body-centered cubic, face-centered cubic, and dual phase (DP) steels was introduced. The application of the cold rollingand subsequent annealing of a martensite starting structure (martensite process) for grain refnement of low-carbon and DPsteels was reviewed. The formation and reversion of strain-induced martensite in metastable austenitic stainless steels andtheir efects on the microstructural evolutions were critically discussed. Moreover, the repetition of the martensite processand its limitations were explained. Important fndings on the SRX of ferrite and austenite for grain refnement as well as therecrystallization kinetics were presented. Finally, the concepts of controlled rolling for grain refnement and the interaction ofaustenite recrystallization and strain-induced precipitation in microalloyed steels during thermomechanical processing werealso reviewed. This short overview presents the opportunities that the conventional and innovative processing routes canofer for grain refnement of steels.