Deposition and Oxidation of Oxide-Dispersed CoNiCrAlY Bondcoats
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itsutoshi Okada, Robert Vassen, Matthias Karger, Doris Sebold, Daniel Mack, Maria Ophelia Jarligo, and Francesco Bozza (Submitted May 9, 2013; in revised form September 20, 2013) CoNiCrAlY powder and nano-size alumina powder were milled by a high-energy-attrition ball-mill, and an oxide-dispersed powder was produced with a mixed structure of metal and alumina in each particle. The oxide-dispersed bond coat powder was deposited by HVOF. Pores, however, were observed in the coating since the alumina was deposited without sufficient melting. Isothermal oxidation tests were carried out for the bond coat specimens at a temperature of 1373 K up to 1000 h in air. As a result, oxidation proceeded inside the coating, since oxygen penetrated through pores formed in the dispersed alumina. However, the authors find that another deposition using higher power levels led to a bond coat without pores. A commercially available oxide-dispersed CoNiCrAlY powder was also deposited by HVOF and VPS, and isothermal oxidation tests were performed. The analysis clarifies that the HVOF bond coat exhibited the thinnest thermally grown oxide than those of the VPS bond coat and conventional metallic bond coat. Furnace cycling tests were conducted using the specimens with an additional ceramic thermal-barrier coating. The specimen with the bond coat sprayed by VPS using commercial oxide-dispersed powder showed almost same number of cycles to delamination compared with the specimen with the conventional metal bond coat.
Keywords
Ball milling, Bondcoats, Composites, Cyclic heating, Oxidation, Powder processing
1. Introduction Thermal-barrier coating (TBC) is applied as well as internal cooling to protect hot-gas-path parts such as blades, vanes, and combustors of gas turbines subjected to high-temperature combustion gas flow. A TBC typically consists of a metallic bondcoat deposited on a nickel- or cobalt-based superalloy and a ceramic topcoat having low thermal conductivity deposited on top. MCrAlY (M is nickel, cobalt, or a combination of the two) is often used as the bondcoat. Since the turbine inlet
This article is an invited paper selected from presentations at the 2013 International Thermal Spray Conference, held May 13-15, 2013, in Busan, South Korea, and has been expanded from the original presentation. Mitsutoshi Okada, Energy Engineering Research Laboratory, Central Research Institute of Electric Power Industry, Yokosuka, Kanagawa, Japan; Robert Vassen, Matthias Karger, Doris Sebold, Daniel Mack, and Maria Ophelia Jarligo, Forschungszentrum Ju¨lich GmbH, IEK-1, Ju¨lich, Germany; and Francesco Bozza, University of Modena and Reggio Emilia, Modena, Italy. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
temperature is increasing for higher thermal efficiency of a combined-cycle power plant, TBCs play increasingly important role. However, topcoat can undergo delamination owing to thermal cycling caused by the startup and shutdown of the power plant, and the microstructural change such as the formation o
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