Effects of temperature and strain rate on deformation behaviour of Inconel 718 alloy

Cylindrical Inconel 718 specimens are compressed dynamically at temperatures ranging from -150 to 550 °C and strain rates in the range of 1000-5000s^-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 impacted at the lowest temperature (-150 °C) and the highest strain rate (5000s^-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^-1 under the considered test conditions. The greatest thermal softening effect occurs in the specimens deformed at the highest strain rate of 5000s^-1 at temperatures of -150 °C and 25 °C, respectively. The microstructural observations confirm that the mechanical response of Inconel 718 is directly related to the effects of the strain rate and temperature on the evolution of the impacted microstructure.