Dynamic Impact Response of Inconel 718 Alloy under Low and High Temperatures

Abstract

Dynamic impact response of Inconel 718 alloy is studied at temperatures ranging from −150 to 550°C and strain rates in the range of 1000 to 5000 s−1 using a compressive split Hopkinson pressure bar. It is found that the flow stress increases with increasing strain rate, but decreases with increasing temperature. The highest work hardening rate is observed in the specimen at the lowest temperature (−150°C) and the highest strain rate (5000 s−1). However, the work hardening rate is weakened by the deformation-induced temperature rise under high strain and strain rate conditions. The strain rate sensitivity increases with increasing strain rate, but decreases with increasing temperature. The activation energy varies as a function of the strain rate and temperature, and has a maximum value of 40 kJ/mol. The greatest thermal softening effect occurs at the highest strain rate of 5000 s−1 and temperatures in the range −150∼25°C. The microstructural observations confirm that the mechanical response of the Inconel 718 specimens is directly related to the effects of the strain rate and temperature on the evolution of the impacted microstructure.