Application-oriented description of time-/temperature dependent crack growth in a conventionally cast nickel-based superalloy

Abstract

The estimation of crack growth (CG) in conventionally cast nickel-based superalloys is of particular interest, since their low ductility and large grain size makes them prone to quasi-brittle fracture. Components made from this material class are often subjected to complex thermo-mechanic fatigue (TMF) loads. CG-testing under TMF loads is expensive and not yet standardized. In addition, many damage mechanisms contribute to the crack growth process under TMF conditions. Nevertheless the need for validated crack growth estimations increases with the demand for flexible load cases.In this work, isothermal and TMF fatigue CG test data of the nickel-based cast alloy C1023 are described by a linear-accumulative CG-model. In this model, fatigue crack growth is treated as temperature-independent. Additionally, two temperature-dependent CG-contributions from creep crack growth and through oxidation damage are considered. γ′-depletion caused by surface oxidation was found to play a dominant role. By dissecting given load cycles into time steps, a revised calculation procedure was implemented to realize estimations for isothermal and thermo-mechanical crack growth, independent from the cyclic time-temperature evolution.The procedure is validated against a variety of CG-experiments, including various TMF-tests with and without hold times. It is also possible to assess the crack evolution and the dominant driver of crack propagation.