Anisothermal high-temperature cyclic behavior of a ni-based single crystal superalloy

Abstract

Dwell-fatigue tests and variable strain rate tensile tests followed by cycling tests were performed using 〈001〉-oriented specimens made of a first-generation Ni-based single crystal superalloy. A short thermal jump from the nominal temperature of 1050°C to 1200°C was introduced along the lifetime of dwell-fatigue experiments and at the beginning of tensile tests. Once such thermal loading was applied, a fine γ′ precipitation occurred in the γ matrix and induced a large transient strengthening effect on the mechanical properties. Indeed, a transient decrease of the plastic strain rate, corresponding to a reduced magnitude in the hysteresis loops, was measured due to the temperature peak during the dwellfatigue experiments. In addition, a temperature peak produced a large hardening effect during the tensile tests since a hardening of 160 MPa was created. These transient phenomena are due a temporary additional strengthening provided by fine γ′ precipitates lasting for the time necessary for their dissolution.