The cyclic stress-strain behavior of nickel-base superalloys—I. Polycrystals

Abstract

The cyclic stress-strain behavior of a wrought, nickel-base superalloy has been investigated at ambient temperature and 843°C with a constant cyclic ramp rate of 10 −2/s. At ambient temperature, the derived cyclic stress-strain curve exhibits three stage behavior, as has been reported under similar conditions for f.c.c. metals. At elevated temperature, the curve is reduced to a power law function with no indication of three stage behavior. The dislocation substructure produced in the intermediate strain range region consists, at both temperatures, of strong persistent slip bands shearing the strengthening γ′ precipitates in the grain interiors and dense dislocation tangles necessitated by near grain boundary strain accommodation. The shapes of the cyclic stress-strain curves are shown to be consistent with the observed dislocation substructures. The cyclic hardening response and details of hysteresis loop shapes were found to be substantially unchanged with temperature.