Maintaining adhesion of protective Al2O3 scales

Smialek, James L.

doi:10.1007/s11837-000-0110-4

Cited by 51 publications

(18 citation statements)

References 22 publications

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“…In addition, free surfaces of such voids can serve as segregation sites for indigenous sulfur also weakening the adhesion of oxide scale and promoting void formation [14,15]. One solution for improving the scale adherence and thus high temperature resistance of superalloys is desulfurization and/or reactive elements (RE) addition that have been proven to provide significant improvements [16,17].…”

Section: Introductionmentioning

confidence: 99%

Characterization of Alumina Scales Grown on a 2nd Generation Single Crystal Ni Superalloy During Isothermal Oxidation at 1050, 1100 and 1150 °C

Swadźba

Wiedermann

et al. 2014

Oxid Met

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This paper concerns microstructural characterization of alumina scales formed on a 2nd generation single crystal Ni superalloy during isothermal oxidation in dry oxygen at 1050, 1100 and 1150°C for 100 h. Samples for high resolution characterization of Al 2 O 3 scales were prepared using a focused ion beam (FIB) method. High resolution TEM and S/TEM techniques were used for a detailed characterization and a direct comparison of the phase composition and chemistry of the oxide scales formed during high temperature oxidation. The growth of transient h-Al 2 O 3 and its transformation to a-alumina is addressed for each oxidation temperature along with the differences in the diffusion of reactive elements, such as Hf, Zr and Y, through grain boundaries of the a phase. The h to a transformation front was proven to move from the metal-scale to the scale-gas interface. The results presented in this paper indicate that after 100 h of oxidation at 1050 and 1100°C there are still some h-alumina grains remaining and even in the regions where the transformation to a was finished the surface retained the whisker-like morphology.

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Section: Introductionmentioning

confidence: 99%

Characterization of Alumina Scales Grown on a 2nd Generation Single Crystal Ni Superalloy During Isothermal Oxidation at 1050, 1100 and 1150 °C

Swadźba

Wiedermann

et al. 2014

Oxid Met

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“…Thus, many hightemperature materials, such as nickel-based superalloys, rely on a slow-growing a-Al 2 O 3 scale for oxidation protection [2]. This scale serves as a barrier which inhibits further reaction between the substrate metal/alloy and the environment, prevents degradation of mechanical properties and subsequent failure of the components.…”

Section: Introductionmentioning

confidence: 99%

High Temperature Oxidation of Pt–Al–Cr–Ru Alloy: Scale Morphology and Adherence

Odusote

Cornish

Papo

2012

Metallogr. Microstruct. Anal.

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Heat-treated Pt-11Al-3Cr-2Ru (at.%) alloy samples were oxidized in air for periods between 1 and 500 h in a muffle furnace at 1350°C. The morphology of the oxidized samples was examined using light microscopy and scanning electron microscopy equipped with energy dispersive spectroscopy, while an x-ray diffractometer and Raman spectroscopy were used for phase identification. The scale layers were found to be composed mainly of a-Al 2 O 3 ; they were adherent, continuous, and protective with neither a zone of discontinuous oxides nor any other internal oxidation. The alumina scale also grew from a submicron thick thin film after 1 h of oxidation to form large irregular-shaped grains after 500 h exposure, indicating increased scale thickness with oxidation time. Good adhesion of the a-Al 2 O 3 scale to the substrate of the current alloy was found to be dependent on the mechanical keying of the scale to the substrate due to protrusions of the alloy into the scale, which gave rise to an irregular scalesubstrate interface. The results suggest that the current alloy has a promising potential for high-temperature applications.

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“…10. 38 These improvements are commercially significant in that low-sulfur single-crystal superalloys are now in production with <1 ppm S, exhibiting greatly improved cyclic oxidation resistance, but perhaps not yet maximized. Segregation predicted by the McLean-Langmuir isotherm suggests that low segregation levels should result for bulk levels of Ä0.1 ppm 37 ( Fig.…”

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confidence: 99%

Advances in the oxidation resistance of high‐temperature turbine materials

Smialek

2001

Surface & Interface Analysis

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This overview highlights some of the key factors in understanding the protective ability of aluminum oxide scales for current gas turbine engine alloys and coatings. Dense, phase-pure, slow-growing and adherent scales are required. In most cases, solutions have been found through educated empiricism, with more complete understanding often lagging by decades. Nevertheless, the relentless application of new techniques to answer old questions has often provided radically different viewpoints and pointed the way to new engineering developments. Equally important, this understanding prevents prior misconceptions from taking too strong a hold and maintaining a limited perspective. The microstructure, kinetics, shortcircuit diffusion, phase transformation, growth and residual stresses, interfacial segregation and adhesion provide a richness of topics for this singular and effective system. Copyright INTRODUCTIONThe successful application of many materials requires excellent high-temperature properties. For example, the thermal materials used in electric furnaces, waste incinerators, boilers, heat exchangers and heat engines all require long-term mechanical and chemical stability at high temperatures. The surface stability of the candidate material is necessary to prevent rapid material consumption at high temperatures. In general, this dictates that the exposed material is able to form a slow-growing, stable, adherent surface scale that serves to protect the underlying substrate material. The most important and effective scales are oxides; they are easily produced by reaction with the oxygen in air or in other oxygen-containing H 2 O, CO 2 or CO gaseous environments. And the most sought-after oxide scales are Al 2 O 3 , Cr 2 O 3 , and SiO 2 because of their outstanding protective qualities. Many of the high-temperature components used in aircraft and ground power gas turbines rely on these scales for protection.The purpose of the present review is to highlight some of the recent advances that have been made to high-temperature, oxidation-resistant turbine materials. It is intended to be neither comprehensive nor critical, but rather to give a general, albeit parochial, synopsis of a number of key issues seen to rise to prominence from the perspective of this author. In light of this venue, an attempt will be made to give special emphasis to advances in understanding and performance that were associated with and facilitated by various characterization and surface analysis techniques. Oxidation primerA few points regarding the basic tenents of oxidation theory relevant to all systems are worth reviewing before dealing with specific issues. (The cardinal reference text on the subject, elegantly covering all aspects in great detail, is that by Kofstad. 1 ) Very briefly, the pertinent control issues are the thermodynamics of the possible gas-solid reactions and the diffusion rates of the oxide scales in the presence of a large oxygen activity (P O 2 ) gradient. The free energy of formation of binary oxides ranges from abou...

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Maintaining adhesion of protective Al2O3 scales

Cited by 51 publications

References 22 publications

Characterization of Alumina Scales Grown on a 2nd Generation Single Crystal Ni Superalloy During Isothermal Oxidation at 1050, 1100 and 1150 °C

Characterization of Alumina Scales Grown on a 2nd Generation Single Crystal Ni Superalloy During Isothermal Oxidation at 1050, 1100 and 1150 °C

High Temperature Oxidation of Pt–Al–Cr–Ru Alloy: Scale Morphology and Adherence

Advances in the oxidation resistance of high‐temperature turbine materials

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