Application of small punch creep testing to a thermally sprayed CoNiCrAlY bond coat

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 585; pp. 205 - 213
• Main Authors: Chen, H., Hyde, T.H., Voisey, K.T., McCartney, D.G.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15-11-2013; Elsevier
• Subjects: Applied sciences; Bonding; Coating; Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder; Creep; Creep (materials); Cross-disciplinary physics: materials science; rheology; Electron back scatter diffraction; Exact sciences and technology; Failure; Fractures; HVOF thermal spraying; Materials science; MCrAlY bond coat; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Mechanical testing; Metals. Metallurgy; Microstructure; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Phase transformation; Physics; Production techniques; Rupture; Surface treatment; Voids; HVOF thermal spraying; MCrAlY bond coat; Phase transformation; Mechanical testing; Creep; FCC lattices; Bond coating; HVOF spraying; Creep test; Creep rate; Crystal defect; Spray coating; EBSD; Grain boundary; Deposition process; Creep fracture; Gamma phase; Test method; Stress effects; Void; Power law; Thermocompression; Grain size; Scanning electron microscopy; Interphase; Cavitation; Mechanical test; Microstructure; Punching test
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2013.06.080

High velocity oxy-fuel thermal spraying was used to prepare free-standing CoNiCrAlY (Co–31.7% Ni–20.8% Cr–8.1% Al–0.5% Y (wt%)) bond coat alloy samples approximately 0.5mm thick. Creep tests were conducted at 750°C on these samples using a small punch (SP) creep test method. The samples were characterised before and after creep testing using scanning electron microscopy with electron backscatter diffraction (EBSD). EBSD revealed a two phase fcc γ-Ni and bcc B2 β-NiAl microstructure with grain sizes ~1–2μm for both phases, which did not change significantly following testing. The constant temperature SP test data were characterised by a minimum creep strain rate, ε̇min, and a total time to failure, tf, at different applied stresses. The data are fitted to conventional power law equations with a stress exponent for creep close to 8 in the Norton power law and between 7 and 10 in the Monkman–Grant creep rupture law. Creep rupture was predominantly due to creep cavitation voids nucleating at both the γ–β interphase boundaries and the γ–γ grain boundaries leading to final failure by void linkage. However, rupture life was influenced by the quantity of oxide entrained in the coating during the spray deposition process.