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Investigation of Techniques and Procedures to Obtain á-Al2O3 Scales on Coatings with Improved Oxidation Resistance

Jackson, Erika Meier (2007) Investigation of Techniques and Procedures to Obtain á-Al2O3 Scales on Coatings with Improved Oxidation Resistance. Master's Thesis, University of Pittsburgh. (Unpublished)

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In this study, two types of coating systems were investigated for their ability to withstand cyclic oxidation conditions. NiCoCrAlY coatings with either 0.1 or 0.5 weight percent yttrium as well as platinum modified aluminide coatings were examined. All of the samples were exposed cyclically, in a bottom-loading furnace at 1100°C in laboratory air. Optical and scanning electron microscopy (SEM) were used to characterize the samples. Various surface treatments were performed on the coatings prior to their exposure. Samples were either exposed as-received, with no treatment, light grit blasted (LGB), light grit blasted and etched with NaOH, or fine polished.The samples containing 0.5 wt.% Y in the as received, LGB and LGB and etched condition, failed by the formation of large oxide protrusions caused by the preferential oxidation of yttrium and by cracking in the coating. The fine polished NiCoCrAlY coatings containing 0.5 wt.%Y did not develop protrusions and did not fail in test. None of the 0.1 wt.%Y coatings with any treatment developed protrusions and none of these failed in test. The PtAl coatings all failed by the formation of large voids at the coating/substrate interface that coalesced and broke through the coating surface, regardless of surface treatment. It was concluded that, in the NiCoCrAlY system, the roughness of the coating surface as well as the amount of yttrium present to oxidize in the coating plays a large role in the coating lifetime. In the PtAl coatings, surface preparation did not appear to have an effect on the coating lifetime. The PtAl coatings and the rough NiCoCrAlY coatings containing 0.5 wt.%Y were found to have similar lifetimes of a few thousand cycles. The polished 0.5 wt.%Y NiCoCrAlY coating and all of the 0.1 wt.%Y coatings exhibited exceptionally long lifetimes, with none of them failing in test.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Jackson, Erika
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairPettit, F.S.pettit@engr.pitt.eduPETTITFS
Committee MemberNettleship, I.nettles@pitt.eduNETTLES
Committee MemberLeonard,
Date: 25 September 2007
Date Type: Completion
Defense Date: 21 May 2007
Approval Date: 25 September 2007
Submission Date: 24 May 2007
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Materials Science and Engineering
Degree: MSMSE - Master of Science in Materials Science and Engineering
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: corrosion; high temperature oxidation; NiCoCrAlY Coating; Platinum Aluminide Coating
Other ID:, etd-05242007-145432
Date Deposited: 10 Nov 2011 19:45
Last Modified: 15 Nov 2016 13:43


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