Hot deformation behavior of the post-cogging FGH4096 superalloy with fine equiaxed microstructure

Hot deformation behavior of the post-cogging FGH4096 superalloy with fine equiaxed microstructure has been characterized by isothermal compression in the temperature (T-d) ranging 1050-1140 degrees C and strain rates ((epsilon) over dot) ranging 0.001-1.0 s(-1). The apparent activation energy of deformation was calculated to be 750 kJ/mol. This value is well above that for the HIPed superalloy, which is believed to attribute to the refinement of grain size and boundary structure after cogging treatment. The constitutive equation that described the flow stress as a function of the strain rate and deformation temperature was proposed for high temperature deformation. The processing maps were constructed to evaluate the efficiency of power dissipation (eta) and recognize the instability regimes for the final-forging process. Optimum parameters were predicted in temperatures of 1080-1110 degrees C and strain rates of 0.1-1.0 s(-1), in which the eta values were higher than others. Otherwise, the plasticity instability was predicted in two regimes, the first of the temperatures of 1100-1120 degrees C and strain rate higher than 0.4 s(-1), and the second of the temperatures lower than 1060 degrees C and strain rates of 0.001-0.4 s(-1). (c) 2011 Elsevier Inc. All rights reserved.