| In order to understand more clearly the hot deformation mechanism of Alloy 718 and consequently to determine the "safe" process design window, a number of compression tests were carried out in the range of temperature, 927℃-1066℃ and strain rate, 5×10^-4/s-5/s up to the true strain of 0.7. Based on dynamic materials model, the optimal process design windows, where the deformation is stable, were proposed through the analysis of the constitutive relationships among true stress, true strain, strain rate and temperature. The instability of deformation was confirmed by observing the microstructure of the compression tested samples. Some characteristic microstructures of the localized deformation, such as twinning and shear band, were observed in the samples deformed under the unstable deformation conditions. |
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