An Empirical Approach to Correlating Thermo-Mechanical Fatigue Behaviour of a Polycrystalline Ni-Base Superalloy

Abstract

Assessment of thermo-mechanical fatigue behaviour of the polycrystalline nickel alloy RR1000 reveals a significant effect of phase angle on fatigue life. The current paper explores two scenarios: the first where the mechanical strain range is held constant and comparisons of the fatigue life are made for different phase angle tests; and secondly, the difference between the behaviour of In-phase (IP) and −180° Out-Of-Phase (OOP) tests over a variety of applied strain ranges. It is shown that different lifing approaches are currently required for the two scenarios, with a mean stress based approach being more applicable in the first case, whereas a Basquin-type model proves more applicable in the second. However, it is also demonstrated that the crack propagation phase should also be considered in these types of tests for high strain ranges and projects that future modelling approaches should attempt to unify mean stress, stress range and a crack propagation phase.

A holistic approach to Thermo-Mechanical Fatigue phase angle effects for an aerospace nickel superalloy

“…For IP and OOP tests of ∆ε=0.8-1.4% and T= 300-700°C, the OOP cycle showed a longer life than IP for ∆ε>1%, but was reversed at lower ∆ε [9]. SC-TMF tests performed at phase angles between IP and OOP showed a consistent increase in TMF life for ∆ε=1% when phase angle progresses from IP to OOP [10]. Examining the mean stress of these tests under stabilised conditions (σ 1/2 life mean ), for CW and IP angles it became more compressive, and, for ACW and OOP angles more tensile, suggesting a potential correlation between σ 1/2 life mean and TMF life [10].…”

Lifing the Effects of Crystallographic Orientation on the Thermo-Mechanical Fatigue Behaviour of a Single-Crystal Superalloy

“…One of the more traditional procedures for the estimation of TMF life is empirical correlation with isothermal low cycle fatigue (LCF) data [7,8]. For polycrystalline alloys, this method has been reasonably successful [4,9,10] but in the case of single crystal superalloys, there are many types of intricate TMF failure mechanisms that can contribute to material damage and make direct correlations with isothermal data difficult. In addition, given the strong anisotropic nature of directionally solidified materials, and the preferred <001> growth orientation of many Ni-based superalloys, an added complexity is present when attempting to derive a model for data that is generated from multiple crystallographic orientations.…”

Advanced Methods for Creep in Engineering Design

“…The shape of a creep curve can vary significantly depending on material and applied conditions [8]. This can have a considerable influence when calculating the lives of engineering components, especially in components where the effects of creep deformation and damage interact with other phenomenon such as fatigue during high-temperature fatigue or thermomechanical fatigue (TMF) [9].…”