Papers by Keyword: Dynamic Recrystallization (DRX)

Abstract: The hot deformation behavior of a nickel based P/M superalloy by spray forming and hot isostaticpressingwas investigated by isothermal compression test at Gleeble 3500 thermal mechanical simulator. The compression test was performed in the temperature ranging from 1025°C to 1150°C and in the strain rate ranging from 10^-1/s to 10^-3/s. The results show that the flow curves of true stress and true strain exhibit typical dynamic recrystallization and dynamic recovery. Compression temperature and strain rate have a strong effect on the dynamic recrystallization grain refinement.With higher strain rate the refined dynamic recrystallizationmicrostructure can be obtained at deformation temperature lower thanγ′solution temperature. Grain coarsening occurs at the deformation temperature close to γ′solution temperature, and the grain grows up obviously with decreasing strain rate.

Abstract: The effect of slow cooling treatment (SCT) on the microstructure and dynamic recrystallization of FGH96 alloy was studied. The results show that the grains of FGH96 alloy after slow cooling rate treatment grow from 20μm~30μm to 30μm~40μm, and the distance between γ′ precipitates in FGH96 alloy becomes larger. This promotes the dynamic recrystallization in the process of hot extrusion and isothermal hot compression and decreases the flow stress effectively.

Abstract: The elevated temperature flow stress behavior of Mg-9Gd-2.5Y-1Nd-0.5Zr magnesium alloy was carried out by Gleeble-1500 thermal mechanical simulator in the temperature range of 460-520°C and in strain rates of 0.0005~1s-1 at a strain of 0.6. The optical microscopy was used for microstructure characterization. The results showed that the flow stress increases with increasing strain rates and decreasing temperature. All the deformed magnesium alloy specimens show a dynamic recovery characters in the temperature range from 460~500°C, and show dynamic recrystallization characters at 520°C. The flow stress of this alloy can be represented by Zener-Hollomon parameter function, and values of related parameters A, α and n, are 2.24×1013s-1、0.027MPa-1 and 2.93, respectively. Its activation energy for hot deformation Q is 212.6kJ/mol.

Abstract: Thermo-Span alloy is an oxidation resistant, low thermal expansion superalloy with good mechanical properties at the service temperature. This paper investigated the hot working behavior of casting Thermo-Span alloy deformed at 900~1150°C, with strains of 20%, 40% and 60% at strain rates of 1 and 10 s^-1. Dynamic recrystallization (DRX) grains were formed at 1110°C with a strain of 20%, at 1050°C with a strain of 40%. Increasing the deformation rate and strain can promote the DRX. However, when the strain exceeded 60% or the deformation temperature was above 1150°C with 40% strain, the surface cracks occurred, indicating that the alloy should be deformed in one heat no larger than 60%. By forging and rolling at 1050°C, Thermo-Span alloy with good surface quality and homogeneous grains was produced, and the tensile properties were still acceptable.

Abstract: The dynamic recrystallization (DRX) of N08028 corrosion resistant alloy was investigated by hot compression tests which were performed at the deformation temperatures from 1000°C to 1200°C and strain rate from 0.01s^-1 to 1s^-1 on a Gleeble-1500 thermo-mechanical simulator. The stress-strain curves at all strain rates showed the characteristics of DRX and exhibited a peak in the flow stress before reaching steady state. The microstructures after deformation demonstrated that DRX took place in all specimens. The results show that DRX occurs more easily with the decrease of strain rate and the increase of deformation temperature. By regression analysis, the activation energy in the entire range of deformation conditions, and the relationship of critical strain as well as strain for 50% DRX with deformation conditions were determined. A good agreement between the experimental and predicted results shows that the proposed DRX kinetic equations can give an accurate estimate of the DRX behavior in hot deformed N08028 corrosion resistant alloy.

Abstract: The high temperature compressive tests of squeeze casting ZK60 magnesium alloy in the testing temperature range of 523-723K and strain rate range of 0.001-10s^-1 were performed on Gleeble-1500D thermal simulator testing machine. Optical microscopy was performed to elaborate on the dynamic recrystallization (DRX) grain growth. TEM observation indicated that the mechanical twinning, dislocation slip, and dynamic recrystallization are the materials typical deformation features. Variations of flow behavior with deformation temperature as well as strain rate were analyzed. Analysis of the flowing deformation behavior and microstructure observations indicated that the flow localization was observed at lower testing temperature and higher strain rates. Dynamic recrystallization occurred at higher testing temperature and moderate strain rates, which improved the ductility of the material. The results indicated that at the testing temperatures lower than 573K and strain rates higher than 1s^-1, the material exhibited flow instability manifesting as bands of flow localizations. These temperatures and strain rates should be avoided in processing the material. Dynamic recrystallization occurs in the temperature range 573-723K and the strain rate range 0.001-0.1s^-1. The number of dynamic recrystallization grains is less at lower temperature and higher strain rate than higher temperature and lower strain rate. The dynamic recrystallization is inadequate at 573-623K while the dynamic recrystallization grain growth has been observed in the temperature range of 673-723K. Therefore it may be considered that the optimum processing parameters for hot working of squeeze casting ZK60 magnesium alloy are 648K and 0.001-0.01s^-1, at which fine dynamic recrystallization microstructure can be obtained.

Abstract: In order to improve the understanding deformation behaviors of thermal compressive of ZK30 magnesium alloy, carried out a series of thermal compressive tests with height reduction 60% of specimens were performed at deformation temperature range of 523-673 K, and strain rates range of 0.001-1 s⁻¹ on Gleeble-1500 thermo-mechanical simulator. Based on an Arrhenius-type equation constructs a nonlinear flow model and its constitutive equation, are employed to study the deformation behavior and the relationship between deformation temperature, strain rate and flow stress. For higher deformation temperature and lower strain rate, the true stress-strain curves show a characteristic of dynamic recrystallization. With the increase of deformation temperature and the decrease of strain rate the flow stress decreases, also the dynamic recrystallization becomes easier.

Abstract: In this work, two approaches for determining critical stress and strain for initiation of dynamic recrystallization (DRX) of the AISI 4340 steel were presented.The first one applied a polynomial function to represent relationship between work hardening rate and flow stress. Secondly, Cingara constitutive model were employed. To investigate hot deformation behavior of the steel, compression tests were performed at different temperatures between 850 °C and 1150 °C and strain rates between 0.01s^-1and 10 s^-1. Obviously, both methods provided different values of critical stress and critical strain.Accuracy of the first method depended on fluctuations of the fitted strain hardening curve. On the other hand, results of the Cingara model was primarily related to the described flow curves up to their peak points. It could be noticed that the DRX occured during hot deformation of the examined steel started when the normalized critical stress and strain reached the values of 0.735 and 0.324, respectively.

Abstract: Deformation behavior of steel 33Μn2v for oil well tube was studied by hot compression tests conducted at various temperatures and strain rates.The Kumar model was developed to predict the hot deformation behavior of steel 33Mn2V for oil well tube.In this regard,the hot compression tests were carried out at the temperatures from 750°C to 1200°C and at the strain rates of 0.02s¹ to 0.16 s¹.The experimental data were then used to determine the constants of developed constitutive equations. The Kumar model can be represented by ZenerHollomon parameter in a hyperbolic sinusoidal equation form.The apparent activation energy of deformation is calculated to be 342.1481kJ/Mol.Dynamic recrystallization of steel 33Mn2V occur and the completion of the critical deformation is small,termination error and the initial deformation is smaller.Therefore,its easy for the steel 33Mn2V to the occurrence and completion of dynamic recrystallization.

Abstract: The dynamic recrystallization of commercially pure titanium was investigated by compression tests on Gleeble-1500D thermal simulation test machine at temperature of 700950 °C and strain rate of 0. 015 s¹. The total compression deformation is 0.7(true strain). The kinetics of dynamic recrystallization of commercially pure titanium at 950 °C was modeled by Avrami equation. The results show that the dynamic recovery and recrystallization obviously occur during compression. The flow stress increases to a peak value and gradually decreases to a steady state. The flow stress is decreased with the increase of deformation temperature and it is increased with the increase of strain rate. The Avrami kinetics model of dynamic recrystallization of commercially pure titanium at 950 °C is obtained .