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2119 |
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Tuesday, May 04, 2010, Sophia Room 4:20 PM Gas Turbines 2 |
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Effect of Ca addition in CoNiCrAlY powder for high temperature oxidation resistance HVOF coatings |
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Luca Lusvarghi / University of Modena and Reggio Emilia , Italy Carlo Giolli / Turbocoating S.p.A, Italy Andrea Scrivani*/ Turbocoating S.p.A, Italy Gabriele Rizzi/ Turbocoating S.p.A, Italy Giovanni Bolelli/ Università di Modena e Reggio Emilia, Italy Ugo Bardi/ Università di Firenze, Italy A. Fossati/ Università di Firenze, Italy Alessandro Lavacchi/ Università di Firenze, Italy M. Di Ferdinando/ Università di Firenze, Italy |
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MCrAlY coatings are used as single overlay coating or as bond coat for thermal barrier coating (TBC) systems. Vacuum plasma spray (VPS) MCrAlY coatings are considered today the state of art. Nevertheless high velocity oxygen fuel (HVOF) sprayed MCrAlY coating is getting always more importance due to its quality and the possibility to reduce costs. On the other hand HVOF process shows some limits. In particular the final coating results to be richer in oxides in comparison with LPPS/VPS MCrAlY coating and it can compromise the high temperature oxidation resistance. This study shows the effect of calcium addition in the commercial CoNiCrAlY powder (AMDRY 995). It is expected that the calcium acts as oxygen getter during the HVOF deposition dwell time saving elements as Al and Y from the oxidation getting better the high temperature oxidation (HTO) resistance of the HVOF coating in comparison with the commercial one. It was study the effect of the Ca during the dwell time of HVOF deposition using TGA and XRF techniques. The HTO resistance of commercial CoNiCrAlY coated by HVOF and VPS on Inconel 738 LC nickel super-alloy was compared with HVOF CoNiCrAlY coating added with Ca. The modified powders showed comparable HTO resistance with VPS coating and better HTO resistance in comparison with HVOF coating. The addition of Ca seems to improve the HTO resistance of commercial CoNiCrAlY coating prepared by HVOF. |