Characterization of thermally cycled alumina scales

Pint, Bruce A.; More, Karren L.; Wright, I.G.; Tortorelli, P.F.

doi:10.1179/mht.2000.024

Cited by 33 publications

(14 citation statements)

References 29 publications

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“…The results of grain boundary elemental mappings indicate temperature dependence of segregant types. However, contrary to this study other studies of Rene N5 oxidized at 1100°C for 100 h did not reveal significant [25] or any [39] Y segregation even at its higher content in the alloy (50 ppm). Additionally no Ta was detected in study [25] at 1100°C while Zr was detected.…”

Section: Reactive Element Effectcontrasting

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: Reactive Element Effectcontrasting

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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“…While MCrAlY-based coatings represent an important class of coatings for current applications, results from this lab suggest that scale adhesion on MCrAlYs is inherently inferior to that on aluminides at 1100°-1200°C [ 6,7] and therefore this coating approach does not represent the most fruitful option for developing high temperature bond coats. Figure 1 compares the temperature dependence of the coefficient of thermal expansion (CTE) of René N5 (Table I) and castings of generic bond coat compositions: NiAl+Hf and NiCoCrAlY.…”

Section: Resultsmentioning

confidence: 99%

“…Similar behavior has been observed for all RE additions. [7,10,17,[23][24][25][26][27][28][29][30] The segregation of Hf ions is the most likely explanation for the low scale growth rate; however, its benefit over other dopants (e.g. Y and Zr), which also segregate at similar levels, has not been explained.…”

Section: Resultsmentioning

confidence: 99%

“…Though not well recognized, the alumina scale adhesion on NiCrAlY-type alloys is decidedly inferior to that formed on REdoped NiAl or FeCrAlY. [6,7] Cast NiCrAlY spalls readily at 1100°C while RE-doped NiAl only spalls after >1000 1h cycles at 1200°C. While Pt does improve scale adhesion in aluminides, its potential is limited compared to Hf additions.…”

Section: Discussionmentioning

confidence: 99%

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Compositional Effects on Aluminide Oxidation Performance: Objectives for Improved Bond Coats

Pint¹,

Haynes²,

More³

et al. 2000

Superalloys 2000 (Ninth International Symposium)

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In order to achieve long thermal barrier coating lifetimes, underlying metallic bond coats need to form adherent, slowgrowing A l 2 O 3 layers. A set of guidelines for developing aluminide bond coat compositions is proposed in order to maximize oxidation performance, i.e. forming a slow-growing adherent alumina scale. These criteria are based on results from cast, model alloy compositions and coatings made in a laboratoryscale chemical vapor deposition facility. Aluminide coatings are thought to have more long-range potential because of their lower coefficient of thermal expansion compared to MCrAlYs. The role of Pt in improving alumina scale adhesion and countering the detrimental role of indigenous sulfur is discussed. However, the improvements associated with Pt are minimal compared to reactive element doping. One strategy which has great promise for improvement is to incorporate Hf into the coating. From an oxidation standpoint, this would preclude the need for Pt in the coating and also reduce the scale growth rate. While excellent oxidation performance was observed for cast Hf-doped NiAl, its benefits can be compromised and even eliminated by co-doping with elements such as Cr,Ti, Ta and Re. Creating a pure Hf-doped NiAl is one promising approach for improving the oxidation performance of bond coats.

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“…For NiAl, these grains result from the transformation of cubic Al 2 O 3 phases (c-and/or h), which form during the initial exposure. Due to the difference between the stable and transient alumina lattice parameters, a layer containing voids is formed between the two regions [2,6,[22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

Grain Boundary Chemistry and Transport Through Alumina Scales on NiAl Alloys

et al. 2017

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It is widely accepted that the growth of protective a-Al 2 O 3 scales on Nibased alloys is governed by the inward diffusion of oxygen through the oxide grain boundaries (GB). However, there is also some outward diffusion of metal ions to the surface, but it is difficult to quantify. In this work we apply atomic force microscopy, scanning electron microscopy and transmission electron microscopy to investigate the outward flux of Al, which manifests as the growth of small ridges along the alumina GBs after the removal of the outermost oxide layer by mechanical polishing or focused ion beam techniques followed by additional oxidation. As a model alumina-former, NiAl with Hf and Zr additions was investigated. In comparison to Zr, Hf was found to reduce the outward Al diffusion. This outward diffusion was six orders of magnitude smaller than the O inward diffusion.

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Characterization of thermally cycled alumina scales

Cited by 33 publications

References 29 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

Compositional Effects on Aluminide Oxidation Performance: Objectives for Improved Bond Coats

Grain Boundary Chemistry and Transport Through Alumina Scales on NiAl Alloys

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