Abstract No.:

Influence of oxidation treatments and surface roughness on the properties of NiCoCrAlY coatings deposited by HVOF

Juan Muñoz Saldaña* / Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico
A.G. Mora-García / Centro de Investigación y de Estudios Avanzados del IPN, México
J.E. García-Herrera/ Centro de Investigación y de Estudios Avanzados del IPN, México
J.M. Alvarado-Orozco/ University of Pittsburg, U.S.A.
C. Poblano-Salas/ Centro de TecnologíaAvanzada, México
G. Trápaga-Martínez/ Centro de Investigación y de Estudios Avanzados del IPN, México
F.J. Espinoza-Beltrán/ Centro de Investigación y de Estudios Avanzados del IPN, México

NiCoCrAlY coatings deposited by high velocity oxygen fuel (HVOF) are widely used in structural applications due to their oxidation and corrosion resistance. These coatings have the ability to form a dense, slow growing and protective oxide scale, typically a-Al2O3 [1]. However, the oxide scale formation is greatly influenced by the oxidation treatments and the surface roughness. Besides this, the formation of such scale is linked to the properties andquality of the coatings which in turn are affected by the deposition conditions [2]. Based on this, the aims of this study are: a) to optimize the properties of NiCoCrAlY coatings by controlling three of the most important HVOF parameters, (fuel-oxygen ratio and spray distance) and b) to evaluate the effect of the oxygen partial pressures (e.g., air and argon), and the surface finishing (e.g., as-coated and as-grinded) on the oxidation behavior, structural, and microstructural properties of optimized NiCoCrAlY coatings. The results show that the as-coated samples oxidized in air developed a thermally grown oxide (TGO) containing mixed oxides such as a-Al2O3, NiO, NiAl2O4 and CoAl2O4 leading to non-protective conditions. Coatings treated in argon mainly show a-Al2O3 formation. Surface treatment by grinding of the coatings prior the oxidation treatment enhanced growth of alumina scale. However, air atmosphereleads totransient alumina and a-Al2O3oxide mixture,while the low oxygen content (argon) allowedthe formation of purea-Al2O3. The microstructural characterization reveals that independent of the oxygen partial pressure, a g/g Al-depleted region was observed at the TGO-coating interface as a result of the bàg transformation.

[1] J.R. Nicholls, N.J. Simms, W. Y. Chang and H. E. Evans, Smart overlay coatings  Concept and practice, Surface and coatings technology,149 (2002) 236-244
[2] L. Pawlowski, The science and engineering of thermal spray coatings, John Wiley & Sons Ltd (2008).

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