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Fatigue damage accumulation in nickel base superalloys.

Lambert, David (1994) Fatigue damage accumulation in nickel base superalloys. PhD thesis, University of Sheffield.

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Abstract

Tangentially oriented Waspaloy specimens taken from the bore section of a turbine disc were subjected to low cycle fatigue in the form of cyclic four point bend tests. Substantial differences in grain size and structure occurred across the section of the disc. Fatigue damage occurred primarily as a result of persistent slip band formation, cell formation, Orowan looping and precipitate shearing. A small number of grains exhibited dislocation cells, normally associated with higher stacking fault energy materials. The number and width of persistent slip bands increased with the number of cycles, but varied both between grains and stress levels. It is proposed that initially looped precipitates were subsequently sheared. Crack initiation was observed as early as 1/12 of fatigue lifetime, predominantly from inclusions. A stage-I/stage-II crack propagation transition occurred at approximate 4Kl values of 30MPa.m1/ 2 , when the plastic zone size was comparable to the material grain size. Results imply that short crack growth requires prior slip band formation.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Materials Science and Engineering (Sheffield)
Identification Number/EthosID: uk.bl.ethos.681739
Depositing User: EThOS Import Sheffield
Date Deposited: 18 Nov 2016 16:42
Last Modified: 18 Nov 2016 16:42
URI: http://etheses.whiterose.ac.uk/id/eprint/15129

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