Hot deformation behaviour of alloy 718 under compression

Compression tests were conducted on Alloy 718 to investigate the high temperature deformation behaviors under wide range of test conditions. Compressive loads were applied up to an axial true strain of 0.7 within the temperature range 954 degrees C to 1066 degrees C and strain rare range 5x10(-4) s(-1) to 5x10(0) s(-1). For most of the test conditions, strain softening occured throughout the deformation due to dynamic recrystallization and recovery processes. The deformed microstructures showed dependence both on strain rate and on test temperature for the given test conditions. At low strain rates, deformation was rather uniform and the deformed microstructure showed a typical view of dynamic recrystallization, In this case, the strain rate sensitivity was about 0.25 and the activation energy was about 432 kJ/mol. With increasing strain rate, deformation became localized and microbands started to form near the grain boundaries, At high strain rate around 5x10(0) s(-1), deformation twins operated as a deformation mechanism.