The Experts below are selected from a list of 63 Experts worldwide ranked by ideXlab platform

Abolfazl Momeni - One of the best experts on this subject based on the ideXlab platform.

  • dynamic recrystallization behavior and constitutive analysis of incoloy 901 under Hot Working Condition
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014
    Co-Authors: Abolfazl Momeni, S M Abbasi, M Morakabati, H Badri, X Wang
    Abstract:

    Abstract Hot deformation behavior of Incoloy 901 Ni-based superalloy was investigated by performing Hot compression tests over the temperature range of 950–1100 °C and at strain rates of 0.001–1 s −1 . The flow curves at low strain rates i.e. 0.001–0.1 s −1 , were characterized by a faint peak or a long plateau after the work hardening region. Only at high strain rates, e.g. 1 s −1 , the flow curves exhibited sharp peaks of dynamic recrystallization. The strain associated with the peak points of flow curves firstly increases with strain rate (up to 0.01 s −1 ) and then unexpectedly decreased at higher strain rates. These anomalous results were attributed to the change in the kinetics of dynamic softening mechanisms. The constitutive analysis of flow stress suggested a change in the Hot deformation behavior of the alloy with increasing temperature (over 1050 °C) or strain rate (over 0.01 s −1 ). Microstructural characterization showed that although dynamic recrystallization would operate over the whole studied ranges of deformation temperature and strain rate, its kinetics was generally sluggish. However, the rate of recrystallization increased remarkably at temperatures beyond 1050 °C or strain rate over 0.01 s −1 . Electron backscattered diffraction (EBSD) measurements and optical microscopy observations showed that the nucleation of recrystallization around the grain boundaries or second-phase particles should be due to the gradual evolution of subgrains.

  • dynamic recrystallization behavior of 13 cr martensitic stainless steel under Hot Working Condition
    Journal of Materials Science & Technology, 2012
    Co-Authors: G R Ebrahimi, H Keshmiri, A R Maldad, Abolfazl Momeni
    Abstract:

    In this study, the efiect of Hot deformation on martensitic stainless steel was carried out in temperatures between 950 to 1100 ‐ C and strain rates of 0.001, 0.01 and 0.1 s i1 . Two important dynamic recrystallization parameters, the critical strain and the point of maximum dynamic softening, were derived from strain hardening rate vs stress curves. Then the calculated parameters were used to predict the dynamic recrystallized fraction. Our results show that critical stress and strain increase with decreasing deformation temperature and increasing strain rate. The Hot deformation activation energy of the steel is also investigated in the present work with 413 kJ/mol. Our experimental ∞ow curves are in fair agreement with the kinetics of dynamic recrystallization model.

Xin Zhang - One of the best experts on this subject based on the ideXlab platform.

  • mechanical and microstructural analysis of 2205 duplex stainless steel under Hot Working Condition
    Journal of Materials Science, 2012
    Co-Authors: A Momeni, K Dehghani, Xin Zhang
    Abstract:

    Hot deformation characteristics of 2205 duplex stainless steel were analyzed by performing Hot compression tests at a temperature range of 950–1200 °C and a strain rate of 0.001–1 s−1. Flow stress was modeled by the constitutive equation of hyperbolic sine function. The constants of n, A, α, and the apparent activation energy were determined at different strains. They were then fitted by polynomial equations. Using the hyperbolic sine function and the relations derived between constants and strain flow curves were successfully modeled. Microstructural evolutions were characterized using optical microscopy and electron back scattered diffraction techniques. The results showed that dynamic recovery in ferrite is accelerated at higher temperatures followed by transformation to continuous dynamic recrystallization. Dynamic recrystallization in austenite was postponed by the accommodation of strain in ferrite and very few internal boundaries in austenite. At high strain rates, dynamic recovery in ferrite and dynamic recrystallization in austenite are very slow. Consequently, the total recrystallized fraction decreases. At low temperatures this situation may cause flow instabilities. At low strain rates, softening processes dominate in austenite and ferrite whereas at intermediate strain rates, the formation of substructures is observed in both phases.

X Wang - One of the best experts on this subject based on the ideXlab platform.

  • dynamic recrystallization behavior and constitutive analysis of incoloy 901 under Hot Working Condition
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014
    Co-Authors: Abolfazl Momeni, S M Abbasi, M Morakabati, H Badri, X Wang
    Abstract:

    Abstract Hot deformation behavior of Incoloy 901 Ni-based superalloy was investigated by performing Hot compression tests over the temperature range of 950–1100 °C and at strain rates of 0.001–1 s −1 . The flow curves at low strain rates i.e. 0.001–0.1 s −1 , were characterized by a faint peak or a long plateau after the work hardening region. Only at high strain rates, e.g. 1 s −1 , the flow curves exhibited sharp peaks of dynamic recrystallization. The strain associated with the peak points of flow curves firstly increases with strain rate (up to 0.01 s −1 ) and then unexpectedly decreased at higher strain rates. These anomalous results were attributed to the change in the kinetics of dynamic softening mechanisms. The constitutive analysis of flow stress suggested a change in the Hot deformation behavior of the alloy with increasing temperature (over 1050 °C) or strain rate (over 0.01 s −1 ). Microstructural characterization showed that although dynamic recrystallization would operate over the whole studied ranges of deformation temperature and strain rate, its kinetics was generally sluggish. However, the rate of recrystallization increased remarkably at temperatures beyond 1050 °C or strain rate over 0.01 s −1 . Electron backscattered diffraction (EBSD) measurements and optical microscopy observations showed that the nucleation of recrystallization around the grain boundaries or second-phase particles should be due to the gradual evolution of subgrains.

G R Ebrahimi - One of the best experts on this subject based on the ideXlab platform.

  • dynamic recrystallization behavior of 13 cr martensitic stainless steel under Hot Working Condition
    Journal of Materials Science & Technology, 2012
    Co-Authors: G R Ebrahimi, H Keshmiri, A R Maldad, Abolfazl Momeni
    Abstract:

    In this study, the efiect of Hot deformation on martensitic stainless steel was carried out in temperatures between 950 to 1100 ‐ C and strain rates of 0.001, 0.01 and 0.1 s i1 . Two important dynamic recrystallization parameters, the critical strain and the point of maximum dynamic softening, were derived from strain hardening rate vs stress curves. Then the calculated parameters were used to predict the dynamic recrystallized fraction. Our results show that critical stress and strain increase with decreasing deformation temperature and increasing strain rate. The Hot deformation activation energy of the steel is also investigated in the present work with 413 kJ/mol. Our experimental ∞ow curves are in fair agreement with the kinetics of dynamic recrystallization model.

  • modeling the flow curve characteristics of 410 martensitic stainless steel under Hot Working Condition
    Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2010
    Co-Authors: A Momeni, G R Ebrahimi, K Dehghani, H Keshmiri
    Abstract:

    The Hot deformation behavior of AISI 410 martensitic stainless steel was investigated by conducting Hot compression tests between 1173 K (900 °C) and 1423 K (1150 °C) and between strain rates of 0.001 s −1 to 1 s −1 . The hyperbolic sine function described the relation well between flow stress at a given strain and the Zener-Hollomon parameter (Z). The variation of flow stress with deformation temperature gave the average value of apparent activation energy as 448 kJ/mol. The strain and stress corresponding to two important points associated with flow curve (i.e., peak strain and the onset of steady-state flow) were related to the Z parameter using power-law equations. A model also was proposed based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation to estimate the fractional softening of dynamic recrystallization at any given strain. This model can be used readily for the prediction of flow stress. The values of n and k, material constants in the JMAK equation, were determined for the studied material. The strains regarding the peak and the onset of steady-state flow were formulated in term of applied strain rate and the constants of the JMAK equation. A good agreement was found between the predicted strains and those obtained by the experimental work.

A Momeni - One of the best experts on this subject based on the ideXlab platform.

  • recrystallization precipitation and flow behavior of d3 tool steel under Hot Working Condition
    Materials Characterization, 2017
    Co-Authors: Zangeneh S Najafi, A Momeni, H R Jafarian, S Ghadar
    Abstract:

    Abstract Hot compression tests were performed on D3 cold-work tool steel at various temperatures of 800–1200 °C and strain rates of 0.001–1 s− 1.The peak stress and strain of flow curves showed uncommon increase within the temperature range of 800–1000 °C and strain rates of 0.001–0.1 s− 1. The dynamic precipitation of fine carbides was found responsible for the observed irregularities. Optical microscopy observations showed the highest rate of precipitation at about 1000 °C. At high strain rates (0.1 or 1 s− 1), the precipitation temperature shifted to around 1100 °C. Observations by optical and FESEM microscopes and EBSD measurements implied that dynamic precipitation could retard dynamic recrystallization at low temperatures and strain rates. Partial dynamic recrystallization mainly occurs by “continuous dynamic recrystallization” and partly by “discontinuous dynamic recrystallization” and “particle stimulated nucleation” mechanisms. More dissolution of carbides, less dynamic precipitation and considerable continuous dynamic recrystallization were the major microstructural phenomena at high temperatures (1100 °C and 1200 °C). The material constants in the hyperbolic sine constitutive equation were determined for low and high temperature regimes. The apparent activation energy for low and high temperature regimes was determined as 566 kJ/moland 564 kJ/mol, respectively.

  • mechanical and microstructural analysis of 2205 duplex stainless steel under Hot Working Condition
    Journal of Materials Science, 2012
    Co-Authors: A Momeni, K Dehghani, Xin Zhang
    Abstract:

    Hot deformation characteristics of 2205 duplex stainless steel were analyzed by performing Hot compression tests at a temperature range of 950–1200 °C and a strain rate of 0.001–1 s−1. Flow stress was modeled by the constitutive equation of hyperbolic sine function. The constants of n, A, α, and the apparent activation energy were determined at different strains. They were then fitted by polynomial equations. Using the hyperbolic sine function and the relations derived between constants and strain flow curves were successfully modeled. Microstructural evolutions were characterized using optical microscopy and electron back scattered diffraction techniques. The results showed that dynamic recovery in ferrite is accelerated at higher temperatures followed by transformation to continuous dynamic recrystallization. Dynamic recrystallization in austenite was postponed by the accommodation of strain in ferrite and very few internal boundaries in austenite. At high strain rates, dynamic recovery in ferrite and dynamic recrystallization in austenite are very slow. Consequently, the total recrystallized fraction decreases. At low temperatures this situation may cause flow instabilities. At low strain rates, softening processes dominate in austenite and ferrite whereas at intermediate strain rates, the formation of substructures is observed in both phases.

  • modeling the flow curve characteristics of 410 martensitic stainless steel under Hot Working Condition
    Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2010
    Co-Authors: A Momeni, G R Ebrahimi, K Dehghani, H Keshmiri
    Abstract:

    The Hot deformation behavior of AISI 410 martensitic stainless steel was investigated by conducting Hot compression tests between 1173 K (900 °C) and 1423 K (1150 °C) and between strain rates of 0.001 s −1 to 1 s −1 . The hyperbolic sine function described the relation well between flow stress at a given strain and the Zener-Hollomon parameter (Z). The variation of flow stress with deformation temperature gave the average value of apparent activation energy as 448 kJ/mol. The strain and stress corresponding to two important points associated with flow curve (i.e., peak strain and the onset of steady-state flow) were related to the Z parameter using power-law equations. A model also was proposed based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation to estimate the fractional softening of dynamic recrystallization at any given strain. This model can be used readily for the prediction of flow stress. The values of n and k, material constants in the JMAK equation, were determined for the studied material. The strains regarding the peak and the onset of steady-state flow were formulated in term of applied strain rate and the constants of the JMAK equation. A good agreement was found between the predicted strains and those obtained by the experimental work.