Recent Advances in Creep Modelling of the Nickel Base Superalloy, Alloy 720Li.

Steve Williams,William Harrison,Mark Whittaker

doi:10.3390/ma6031118

Steve Williams, William Harrison + Show 1 more

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https://doi.org/10.3390/ma6031118

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Abstract

Recent work in the creep field has indicated that the traditional methodologies involving power law equations are not sufficient to describe wide ranging creep behaviour. More recent approaches such as the Wilshire equations however, have shown promise in a wide range of materials, particularly in extrapolation of short term results to long term predictions. In the aerospace industry however, long term creep behaviour is not critical and more focus is required on the prediction of times to specific creep strains. The current paper illustrates the capability of the Wilshire equations to recreate full creep curves in a modern nickel superalloy. Furthermore, a finite-element model based on this method has been shown to accurately predict stress relaxation behaviour allowing more accurate component lifing.

Highlights

Nickel-base superalloys perform a key role in gas turbine aero engines due to their superior mechanical properties at elevated temperatures and good corrosion resistance
This stress redistribution will be as a result of creep deformation at the high temperatures experienced in the component, at stress raising features such as blade loading slots, which experience the highest temperatures due to their proximity to the disc rim, and the hot gas stream
The stress and temperature dependence of the creep properties of Alloy 720Li predicted using a traditional power law approach are expressed by the stress exponent n and the activation Qc in Equation (2)

Summary

Introduction

Nickel-base superalloys perform a key role in gas turbine aero engines due to their superior mechanical properties at elevated temperatures and good corrosion resistance. This high temperature strength is usually provided by a distribution of γ’(Ni3(Al,Ti)) precipitates which hinder dislocation movement. Whilst the operating life of the disc will be fatigue dominated, in order to affect an accurate fatigue life prediction it is critical that the redistribution of stresses at high temperatures be well understood This stress redistribution will be as a result of creep deformation at the high temperatures experienced in the component, at stress raising features such as blade loading slots, which experience the highest temperatures due to their proximity to the disc rim, and the hot gas stream

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