Papers by Keyword: Hot Deformation

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Authors: Feng Bo Han, Jin Shan Li, Hong Chao Kou, Bin Tang, Min Jie Lai, Hui Chang
Abstract: A constitutive model using dislocation density rate as an internal state variable has been proposed for hot working of β titanium alloy in this paper. The β phase was only taken into consideration during high temperature deformation. The solution strengthening and dislocation interaction were included in the constitutive equations. The strength coefficient was determined by equivalent vanadium content, Veq, which was calculated according to the alloy constituent. A Kocks-Mecking model was adopted to describe the variation of dislocation density. The constitutive relationship of a β titanium alloy Ti-10V-4.5Fe-1.5Al for high temperature deformation was established using the internal-state-variable based model. Model parameters were determined by the genetic algorithm based objective optimization method. The predicted results agree fairly well with the experimental value.
Authors: Hong Ke Wang, Li Wen Zhang, Sen Dong Gu, Qiu Hong Quan, Wen Fei Shen
Abstract: The dynamic recrystallization (DRX) behavior of GH80A superalloy was investigated by isothermal compression tests on a Gleeble1500 thermomechanical simulator. True stress-strain curves and deformed specimens were obtained at the temperature range of 1273-1473K and the strain rate range of 0.01-5s-1. Experimental results show that the stress-strain curves at low strain rate display a typical DRX characteristic. By regression analysis of experimental results, Materials constant n, activation energy Q and Zener-Hollomon (Z) parameter were determined, and the critical strain model and austenite grain size model for dynamic recrystallization were established as a function of deformation temperature and strain rate. The dynamic recrystallization kinetic model for GH80A was established on the basis of the Avrami equation.
Authors: Arthur Galiyev, Rustam Kaibyshev, Taku Sakai
Authors: Chao Bei Hu, Bao Feng Guo, Yongtao Zhang, Miao Jin, Guan Qiang Yang, Ming Fang Ma
Abstract: Calculation of the critical condition for the initiation of DRX is of considerable interest for the modeling of industrial processes but it strongly depends on the chemical composition of the material, the grain size prior to deformation, and the deformation conditions ( T and ε ). This paper was therefore to show an approach that allows for accurate but convenient identification of the occurrence of DRX. For a Fe-Cr-Ni super stainless steel, the results show that there is a linear relationship between σc and lnZ ( σc=457.26-12.52lnZ). In addition, within the entire range of temperature and strain rate studied, it can be found that the values of both σc and σp or εc and εp keep similar variation trends, respectively. Finally, it was found that the critical ratios of both σc/σp and εc/εp remain fairly constant (≈0.92 and ≈0.47, respectively).
Authors: Tatsuhiko Aizawa, Fujio Tsumori
Authors: Stéphane Godet, Ph. Harlet, Francis Delannay, Pascal J. Jacques
Authors: Chao Bei Hu, Bao Feng Guo, Yongtao Zhang, Miao Jin, Ming Fang Ma, Guan Qiang Yang
Abstract: In constant strain rate tests, the occurrence of dynamic recrystallization (DRX) is traditionally identified from the presence of stress peaks in flow curves. However, not all materials display well-defined peaks when tested under these conditions. It is shown that the onset of DRX can also be identified from the inflection point on the strain hardening rate (θ=dσ/dε)versus flow stress (σ) curve. In this paper, the hot compression curves can be described by an equation that fits the experimental θ-σ data from zero to the peak stress. An appropriate third order equation was fitted to the strain hardening data. The results show that the critical stress at initiation σc=-B/3A where A and B are coefficients of the third order equation. It is evident that this value depends on the deformation conditions. The stress–strain curve was then normalized with respect to the peak stress, leading to a normalized value of the critical stress (uc) equal to uc=σc/σp=-B'/3A'. Here A'and B'are coefficients of the normalized third order equation. This value is constant and independent of the deformation conditions.
Authors: Pavel Lukáč, Tibor Donič, Mária Chalupová, Peter Palček, Zuzanka Trojanová, Eva Tillová, Stanislav Rusz, Ronald Bastovansky
Abstract: Magnesium alloy EZ10 was deformed in tension at temperatures from room temperature up to 400 °C with an initial strain rate of 2.7x10-3 s-1. Deformation tests showed a rapid decrease of the tensile yield strength at temperatures higher than 300 °C. Microstructure of the deformed samples was analysed with light microscope. Fracture mechanisms were estimated using scanning electron microscopy.
Authors: Xin Zhao, Kui Zhang, Xing Gang Li, Yong Jun Li, Kang Zhang, Shi Wei Li
Abstract: The characteristic of dynamic recrystallization (DRX) in Mg-Y-Nd-Gd-Zr magnesium alloy had been investigated by compression test at temperatures between 523 and 723K and the strain rates ranging from 0.002 to 1s-1with maximum strain of 0.693. The flow behavior was described by a power exponent function. Processing map of this alloy was established on the basis of dynamic material model. Microstructure observations suggested that the peak value of dissipation factor was 0.36 at the temperature of 673K and the strain rate of 1s-1. The map exhibits flow instabilities as two domains, one is at the lower temperatures but higher strain rates, and the other is at higher temperatures and lower strains.The region at an intermediate temperature and a high strain rate is the region of the optimal mechanical working properties.
Authors: Ying Gong
Abstract: The compression test on TC21 titanium alloy was carried out in the temperature range of 860~940oC and the strain rate range of 0.01~10s-1 on Gleeble-1500D hot simulation machine. And the hot deformation behavior was studied. The processing map was calculated and analyzed according the dynamic materials model. It is found that the flow stress of TC21 decreases with the increasing of the temperature and the decreasing of the strain rate. The flow stress curves are characterized by steady state at low strain rate( s-1)but discontinuous yield at high strain rate( s-1). The processing map established at the true strain of 0.4 shows that there are three regions, instability and safe and peak region, and the efficiencies of power dissipation are 0~25%,31%~37% and 43%~49% respectively. The peak region is the optimum hot working zone of TC21 titanium alloy.
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