An investigation into static crack growth and dwell-fatigue in the nickel based superalloy RR1000 at elevated temperatures

Baker, Scarlett (2011). An investigation into static crack growth and dwell-fatigue in the nickel based superalloy RR1000 at elevated temperatures. University of Birmingham. M.Res.

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Abstract

This study aims to investigate the crack growth performance of the high strength superalloy RR1000 at elevated temperatures. Within the aero-engine RR1000 is subjected to fatigue and dwell-fatigue where crack growth can occur via creep and oxidation in addition to fatigue. The potentially dominating static crack growth mechanism has resulted in a focus upon static load testing in this study. Post-testing fractography, grain size measurements and metallographic examination have been carried out in order to better understand crack growth behaviour.
Parent specimens were tested under fatigue-dwell conditions over the temperature range 600-700°C. The tests revealed that extended periods of dwell have a detrimental effect upon crack growth resistance in air. Such crack growth exhibited a fully intergranular cracking mechanism. It has been shown that dwell-fatigue loading conditions are greatly influenced by increasing test temperature and therefore suggested that the rate of oxygen diffusion is a controlling factor causing crack growth.
Inertia welded (IW) specimens were tested in air over the temperature range 500-700°C with two samples also tested in vacuum at 700°C. IW specimens exhibited a significantly lower crack growth resistance compared to the parent alloy with evidence that sustained loading has a dominant effect on crack growth for high values of stress intensity factor, K. A vast improvement in crack growth resistance is apparent for the vacuum samples in comparison to the samples tested in air.
Welding processing parameters were investigated by static load testing as-welded and post-weld heat treated (PWHT) linear friction welded (LFW) specimens over a range of welding energy input rates. It was revealed that energy input rate has a notable effect on crack growth in the as-welded condition but a negligible effect after PWHT. The more symmetrical crack profiles produced as a result of PWHT have suggested a controlling influence of residual stress upon such crack growth resistance curves

Type of Work:

Thesis (Masters by Research > M.Res.)

Award Type:

Masters by Research > M.Res.

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