Hot Deformation Behavior of Superalloy 718

The hot deformation behavior of Alloy 718 was characterized on the basis of the dynamic materials model and compression data in the temperature range of 900 to 1177C and strain rate range of 0.005 to 5s'. The flow curves at all temperatures and strain rates showed little dependence on strains larger than 0.3. Constitutive equations were used to characterize the dependence of flow stress on strain, strain rate and temperature. A threedimensional distribution of strain rate sensitivity with strain rate and temperature revealed a decrease in sensitivity with an increase in strain rate and a decrease in temperature. A processing (power dissipation) map constructed from the dynamics materials model and the corresponding isoefficient contours at a strain of 0.5 exposed a domain of peak efficiency of 35 % at temperatures of 1132 to 1177C and the strain rates of 0.05 to 0.5 set", which would be optimum parameters for hot working. These results are in good agreement with previous recrystallization-temperature-time maps reported in the literature. The activation energy for plastic flow in the 900 to 1177C range was about 483 KJ/mole, and the constitutive relationship between flow stress and temperature compensated strain rate (Zener-Hollomon parameter) was found to be valid in the temperature range of 900 to 1177C.