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Title: Examination of the platinum effect on the oxidation behavior ofnickel-aluminide coatings

Abstract

Oxidation resistant nickel-aluminide coatings are designed to develop a protective alumina scale during high temperature exposure. It is well established that platinum additions, typically about 6-8 at%, provide substantial improvements in oxidation resistance of such coatings, yet the nature of the platinum effect is still not fully understood. In this work, the oxidation behavior of two commercial NiAl and NiPtAl coatings deposited on the same Ni-base single crystal alloy CMSX-4 was analyzed. Cyclic and isothermal oxidation tests were conducted at 1150 C in air. Microstructure development and alumina/coating interface chemistry were studied as a function of oxidation time. Numerous voids developed at the Al{sub 2}O{sub 3}/NiAl interface, and sulfur was found to segregate at the void surfaces and at the contact interface, leading to spallation of the scale over the convex areas along ridges on the coating surface. The presence of platinum prevented sulfur segregation and void formation at the Al{sub 2}O{sub 3}/NiPtAl interface. As a result, the Al{sub 2}O{sub 3} scale on the NiPtAl coating remained adherent and virtually no spallation was observed even after prolonged cyclic oxidation.

Authors:
;
Publication Date:
Research Org.:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org.:
USDOE Director. Office of Science. Basic EnergySciences
OSTI Identifier:
923207
Report Number(s):
LBNL-62479
R&D Project: 503001; BnR: KC0201020; TRN: US200804%%1027
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Conference
Resource Relation:
Conference: International Conference on MetallurgicalCoatings and Thin Films, San Diego, CA, April 23-27,2007
Country of Publication:
United States
Language:
English
Subject:
36; AIR; ALLOYS; CHEMISTRY; COATINGS; MICROSTRUCTURE; MONOCRYSTALS; OXIDATION; PLATINUM; PLATINUM ADDITIONS; SEGREGATION; SPALLATION; SULFUR; THIN FILMS

Citation Formats

Hou, Peggy Y., and Tolpygo, V.K. Examination of the platinum effect on the oxidation behavior ofnickel-aluminide coatings. United States: N. p., 2007. Web.
Hou, Peggy Y., & Tolpygo, V.K. Examination of the platinum effect on the oxidation behavior ofnickel-aluminide coatings. United States.
Hou, Peggy Y., and Tolpygo, V.K. Tue . "Examination of the platinum effect on the oxidation behavior ofnickel-aluminide coatings". United States. doi:. https://www.osti.gov/servlets/purl/923207.
@article{osti_923207,
title = {Examination of the platinum effect on the oxidation behavior ofnickel-aluminide coatings},
author = {Hou, Peggy Y. and Tolpygo, V.K.},
abstractNote = {Oxidation resistant nickel-aluminide coatings are designed to develop a protective alumina scale during high temperature exposure. It is well established that platinum additions, typically about 6-8 at%, provide substantial improvements in oxidation resistance of such coatings, yet the nature of the platinum effect is still not fully understood. In this work, the oxidation behavior of two commercial NiAl and NiPtAl coatings deposited on the same Ni-base single crystal alloy CMSX-4 was analyzed. Cyclic and isothermal oxidation tests were conducted at 1150 C in air. Microstructure development and alumina/coating interface chemistry were studied as a function of oxidation time. Numerous voids developed at the Al{sub 2}O{sub 3}/NiAl interface, and sulfur was found to segregate at the void surfaces and at the contact interface, leading to spallation of the scale over the convex areas along ridges on the coating surface. The presence of platinum prevented sulfur segregation and void formation at the Al{sub 2}O{sub 3}/NiPtAl interface. As a result, the Al{sub 2}O{sub 3} scale on the NiPtAl coating remained adherent and virtually no spallation was observed even after prolonged cyclic oxidation.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}

Conference:
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  • Cyclic oxidation behavior of aluminide, platinum modified aluminide, and MCrAlY coating has been investigated at three temperatures. Aluminide and platinum modified coating were deposited on GTD 111 material using an outward diffusion process. CoCrAlY coating was applied on GTD-111 by Electron Beam Physical Vapor Deposition (EB-PVD). The oxidation behavior of these coatings is characterized by weight change measurements and by the variation of {beta} phase present in the coating. The platinum modified aluminide coating exhibited the highest resistance to oxide scale spallation (weight loss) during cyclic oxidation testing. Metallographic techniques were used to determine the amount of {beta} phase andmore » the aluminum content in a coating as a function of cycles. Cyclic oxidation life of these coatings is discussed in terms of the residual {beta} and aluminum content present in the coating after exposure. These results have been used to calibrate and validate a coating life model (COATLIFE) developed at the Material Center for Combustion Turbines (MCCT).« less
  • The adhesion of alumina scales to aluminide bond coats is a life-limiting factor for some advanced thermal barrier coating systems. This study investigated the effects of aluminide bond coat sulfur and platinum contents on alumina scale adhesion and coating microstructural evolution during isothermal and cyclic oxidation testing at 1150 C. Low-sulfur NiAl and NiPtAl bond coats were fabricated by chemical vapor deposition (CVD). Lowering the sulfur contents of CVD NiAl bond coatings significantly improved scale adhesion, but localized scale spallation eventually initiated along coating grain boundaries. Further improvements in scale adhesion were obtained with Pt additions. The observed influences ofmore » Pt additions included: (1) mitigation of the detrimental effects of high sulfur levels, (2) drastic reductions in void growth along the scale-metal interface, (3) alteration of the oxide-metal interface morphology, and (4) elimination of Ta-rich oxides in the Al{sub 2}O{sub 3} scales during thermal cycling. The results of this study also suggested that the microstructure (especially the grain size) of CVD aluminide bond coatings plays a significant role in scale adhesion.« less
  • The present study focused on the effect of N in ferritic Fe-9Cr-1Mo and austenitic 304 L alloy substrates on the formation and cyclic oxidation behavior of aluminide coatings fabricated by chemical vapor deposition (CVD). Relatively high N contents in the commercial alloys caused the formation of AlN precipitates in the CVD aluminide coating, which adversely affected the adhesion of the as-deposited coatings, particularly on 304 L. The reduction of N content in the substrate alloys resulted in a cleaner coating layer with fewer precipitates and Kirkendall voids. However, the cyclic oxidation behavior of the aluminide coatings in air + 10more » vol.% H{sub 2}O at 700 C was not noticeably changed by the N reduction« less
  • The isothermal and cyclic oxidation behavior of a new class of damage-tolerant niobium aluminide (Nb{sub 3}Al-xTi-yCr) intermetallics is studied between 650 C and 850 C. Protective diffusion coatings were deposited by pack cementation to achieve the siliciding or aluminizing of substrates with or without intervening Mo or Ni layers, respectively. The compositions and microstructures of the resulting coatings and oxidized surfaces were characterized. The isothermal and cyclic oxidation kinetics indicate that uncoated Nb-40Ti-15Al-based intermetallics may be used up to {approximately}750 C. Alloying with Cr improves the isothermal oxidation resistance between 650 C and 850 C. The most significant improvement inmore » oxidation resistance is achieved by the aluminization of electroplated Ni interlayers. The results suggest that the high-temperature limit of niobium aluminide-based alloys may be increased to 800 C to 850 C by aluminide-based diffusion coatings on ductile Ni interlayers. Indentation fracture experiments also indicate that the ductile nickel interlayers are resistant to crack propagation in multilayered aluminide-based coatings.« less
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