Hot deformation characteristics of INCONEL alloy MA 754 and development of a processing map

Abstract

The characteristics of hot deformation of INCONEL alloy MA 754 have been studied using processing maps obtained on the basis of flow stress data generated in compression in the temperature range 700°C to 1150°C and strain rate range 0.001 to 100 s^-1. The map exhibited three domains. (1) A domain of dynamic recovery occurs in the temperature range 800°C to 1075°C and strain rate range 0.02 to 2 s^-1, with a peak efficiency of 18 pct occurring at 950°C and 0.1 s^-1. Transmission electron microscope (TEM) micrographs revealed stable subgrain structure in this domain with the subgrain size increasing exponentially with an increase in temperature. (2) A domain exhibiting grain boundary cracking occurs at temperatures lower than 800°C and strain rates lower than 0.01 s^-1. (3) A domain exhibiting intense grain boundary cavitation occurs at temperatures higher than 1075°C. The material did not exhibit a dynamic recrystallization (DRX) domain, unlike other superalloys. At strain rates higher than about 1 s^-1 the material exhibits flow instabilities manifesting as kinking of the elongated grains and adiabatic shear bands. The material may be safely worked in the domain of dynamic recovery but can only be statically recrystallized.