Insight into the Process-Microstructure-Property Relationship: Single Splat Analysis, Adhesion Testing, and Thermal Cycling of Inner Diameter (ID) Thermal Barrier Coatings

Insight into the Process-Microstructure-Property Relationship: Single Splat Analysis, Adhesion Testing, and Thermal Cycling of Inner Diameter (ID) Thermal Barrier Coatings | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Insight into the Process-Microstructure-Property Relationship: Single Splat Analysis, Adhesion Testing, and Thermal Cycling of Inner Diameter (ID) Thermal Barrier Coatings Maheshwar Rao Bagathi, Jonas Frederik Zajaczkowski, Wolfgang Tillmann, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8250483/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Although inner-diameter (ID) thermal barrier coating (TBC) processes are well-established for large aero/land-based turbine liners, the relationships between the processes, microstructures, and properties of coatings applied to smaller, highly confined passages (ID < 200 mm), such as combustor liners, exhaust manifolds, and pipes that face comparable thermal loads, remain largely undocumented. This study examines 8 wt.% YSZ topcoats, which are deposited using an ID-atmospheric plasma spray (APS) torch, as well as bond coats, which are deposited using an ID-high velocity oxyfuel (HVOF) torch, inside 200 mm diameter, 8 mm wall tubes. The results are then compared with those of flat substrates sprayed under otherwise identical conditions. Single splats of YSZ demonstrate that oblique impact angles imposed by the tube create splashed lamellae, resulting in slightly higher local porosity than on flat substrates. Pull-off tests reveal the adhesion strengths of ID TBCs when sprayed using the two ID spraying systems. Two types of topcoat microstructures were developed using a lower-power ID-APS torch: porous variants with different porosities ranging from 9% to 17 vol% and a dense, vertically cracked (DVC) variant. The microstructures were subjected to (i) burner-rig thermal-gradient cycling and (ii) 1100°C furnace cycling. In the burner rig, lifetime scales with the through-thickness temperature gradient and bond-coat thickness. The best porous ID coating endured 246 cycles, while the specimen with a thin bond coat failed abruptly after 101 cycles. Furnace tests impose uniform oxidation; all porous coatings spalled between 60 and 100 cycles, and the DVC cracked after 40 cycles. The failure modes indicate, respectively, oxidation-driven delamination of the ceramic from the bond coat and cracking through the ceramic topcoat. In conclusion, disk-type splat formation, adequate bond coat thickness, and sufficient top coat porosity are microstructural prerequisites for durable ID-TBCs, providing a process map for future ID applications. Materials Engineering Internal-diameter (ID) thermal-barrier coating systems (TBC) atmospheric plasma spraying (APS) splat morphology coating adhesion burner-rig cycling isothermal oxidation porous top coat dense vertical cracked top coat (DVC) bond coat Full Text Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8250483","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":553415214,"identity":"651cf1e6-b6dd-4106-a2ef-3d2e06ad4d73","order_by":0,"name":"Maheshwar Rao Bagathi","email":"","orcid":"","institution":"Forschungszentrum Jülich GmbH","correspondingAuthor":false,"prefix":"","firstName":"Maheshwar","middleName":"Rao","lastName":"Bagathi","suffix":""},{"id":553415215,"identity":"122f1b7b-a69e-4c4a-80e5-3655ba25ef43","order_by":1,"name":"Jonas Frederik Zajaczkowski","email":"","orcid":"","institution":"TU Dortmund 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Coatings\u003c/p\u003e","fulltext":[],"fulltextSource":"","fullText":"","funders":[{"identity":"8d5f59fb-afab-42df-9378-a7b989ad7a20","identifier":"10.13039/501100001659","name":"Deutsche Forschungsgemeinschaft","awardNumber":"456827225","order_by":0}],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Forschungszentrum Jülich","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Internal-diameter (ID), thermal-barrier coating systems (TBC), atmospheric plasma spraying (APS), splat morphology, coating adhesion, burner-rig cycling, isothermal oxidation, porous top coat, dense vertical cracked top coat (DVC), bond coat","lastPublishedDoi":"10.21203/rs.3.rs-8250483/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8250483/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAlthough inner-diameter (ID) thermal barrier coating (TBC) processes are well-established for large aero/land-based turbine liners, the relationships between the processes, microstructures, and properties of coatings applied to smaller, highly confined passages (ID\u0026thinsp;\u0026lt;\u0026thinsp;200 mm), such as combustor liners, exhaust manifolds, and pipes that face comparable thermal loads, remain largely undocumented. This study examines 8 wt.% YSZ topcoats, which are deposited using an ID-atmospheric plasma spray (APS) torch, as well as bond coats, which are deposited using an ID-high velocity oxyfuel (HVOF) torch, inside 200 mm diameter, 8 mm wall tubes. The results are then compared with those of flat substrates sprayed under otherwise identical conditions. Single splats of YSZ demonstrate that oblique impact angles imposed by the tube create splashed lamellae, resulting in slightly higher local porosity than on flat substrates. Pull-off tests reveal the adhesion strengths of ID TBCs when sprayed using the two ID spraying systems. Two types of topcoat microstructures were developed using a lower-power ID-APS torch: porous variants with different porosities ranging from 9% to 17 vol% and a dense, vertically cracked (DVC) variant. The microstructures were subjected to (i) burner-rig thermal-gradient cycling and (ii) 1100\u0026deg;C furnace cycling. In the burner rig, lifetime scales with the through-thickness temperature gradient and bond-coat thickness. The best porous ID coating endured 246 cycles, while the specimen with a thin bond coat failed abruptly after 101 cycles. Furnace tests impose uniform oxidation; all porous coatings spalled between 60 and 100 cycles, and the DVC cracked after 40 cycles. The failure modes indicate, respectively, oxidation-driven delamination of the ceramic from the bond coat and cracking through the ceramic topcoat. In conclusion, disk-type splat formation, adequate bond coat thickness, and sufficient top coat porosity are microstructural prerequisites for durable ID-TBCs, providing a process map for future ID applications.\u003c/p\u003e","manuscriptTitle":"Insight into the Process-Microstructure-Property Relationship: Single Splat Analysis, Adhesion Testing, and Thermal Cycling of Inner Diameter (ID) Thermal Barrier Coatings","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-02 14:09:31","doi":"10.21203/rs.3.rs-8250483/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"416b5895-a3b1-4788-b1b4-8d1bcdbeac8b","owner":[],"postedDate":"December 2nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":58886045,"name":"Materials Engineering"}],"tags":[],"updatedAt":"2025-12-02T14:09:31+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-02 14:09:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8250483","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8250483","identity":"rs-8250483","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}