Low-cycle fatigue of a nickel-based superalloy at high temperature: Simplified micromechanical modelling

TL;DR

This paper develops a simplified micromechanical model to predict low-cycle fatigue behavior of a high-temperature nickel-based superalloy, considering internal stresses and slip system activation.

Contribution

It introduces a novel simplified composite approach to model internal stresses and slip activation in superalloys during low-cycle fatigue at high temperatures.

Findings

Predicted slip system activation patterns under various loading conditions.

Demonstrated the influence of internal stresses on fatigue behavior.

Correlated microstructural evolution with experimental data.

Abstract

This work is focused on the micromechanical modelling of the low cycle fatigue of the nickel based $\gamma/\gamma'$ superalloy AM1 at high temperature. The nature of the activated slip systems in the different types of channels of the $\gamma$ phase is analysed, taking into account the combined effects of the applied and internal stresses. The latter are split into two contributions, misfit stresses and compatibility stresses between the elastic $\gamma'$ phase and the elasto-plastic $\gamma$ phase, which are estimated within a simplified composite approach. Internal stresses may induce slip activity and/or be relaxed by it, which results in a complex sequence of slip activation events in the different channels under increasing applied stress. The consideration of these effects leads to a prediction of the nature and distribution of the active slip systems within the channels in [001] tension, compression and during low cycle fatigue. The resulting microstructural behaviour and its consequences regarding the anisotropic nature of the coalescence of the $\gamma'$ precipitates are discussed with respect to the available experimental data.