Papers by Keyword: Hot Deformation Behaviour

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Authors: A. Colin, Christophe Desrayaud, Marie Mineur, Frank Montheillet
Abstract: The aim of this work is to study the flow instabilities occurring during hot forging of titanium alloy blades. In this view, the viscoplastic deformation behaviour of Ti-6Al-4V alloy is investigated by means of torsion tests under isothermal hot working conditions at temperatures ranging from 800 to 1020 °C and strain rates of 0.01, 0.1 and 1s−1. The thermomechanical processing is performed up to a true strain of 10. The flow stress data are analysed in terms of strain rate and temperature sensitivities. A constitutive equation that relates not only the dependence of the flow stress on strain, strain rate and temperature, but also for the fraction of each phase α and β is proposed. Two mechanical models are compared : the uniform strain rate model (Taylor) and the uniform plastic energy model (IsoW). The usual strain rate sensitivity and activation energy values of Ti-6Al-4V alloy are obtained by fitting the experimental data. Furthermore, specific values of strain rate sensitivities and activation energies are calculated for the α and β phases providing thus a constitutive law based on the physics of the α / β phase diagram. The flow stress is then related to strain by an empirical equation taking into account the flow softening observed after a true strain of 0.5 and the steady state flow reached after a true strain of 4. Comparison of the calculated and measured flow stresses shows that the constitutive equation predicts the experimental results with a reasonable accuracy. The above constitutive equation is then used for simulating forging processes by the finite element method. The calculations exhibit the localisation of deformation produced by shearing effects in the form of the classical X shape.
Authors: Hui Qin Chen, Hao Zhuan Lin, L. Guo, Chun Xiao Cao
Abstract: The hot deformation behavior of TC11 with an equiaxed α+β pre-form microstructure was investigated by hot compression tests in the temperature range 800°C–1090°C and strain rate range 1×10-310s-1. Several approaches have been used in this investigation, which include analysis of shapes of stress–strain curves, kinetic analysis and microstructure observation. The experimented results showed that, (1) In the β phase field, the alloy exhibits dynamic re-crystallization. The apparent activation energy in this domain is estimated to be 183kJ/ mol, which is close to that for self-diffusion in β. The re-crystallized grain size may be governed by competing of diffusion and dynamic re-crystallization rate at deforming conditions. (2) In the α+β phase field, the alloy exhibits super-plastic deformation behavior at 0.001-0.01s-1 and 980°C -850°C, and the apparent activation energy estimated in this domain is about 600 kJ/mol, which is much higher than that for self-diffusion in α-titanium due to β volume fraction is not constant over the test temperature range.
Authors: Zhou Li, Guo Qing Zhang, Shi Fan Tian, Ming Gao Yan
Abstract: Microstructures and hot deformation behaviors of spray formed superalloy GH742 have been studied in this paper. The results indicate that the spray formed superalloy GH742 has high relative density, low oxygen pickup, refined microstructure, and good forgeability. The fully inhibited coarsening of microstructure in spray formed superalloy GH742 has also been found in this study. 32wt% γ¢ and 0.5wt% carbonitrides, (Nb,Ti)(C,N) and Ti(C,N) were found in the as-deposited GH742, and most of them are sub-micrometer.
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