Effects of segregating elements on the adhesive strength and structure of the α-Al2O3/β-NiAl interface

Carling, Karin M.; Carter, Emily A.

doi:10.1016/j.actamat.2006.12.020

Cited by 101 publications

(43 citation statements)

References 47 publications

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“…They concluded that pre-oxidation of Ni 3 Al and thus formation of a thin Al 2 O 3 layer improved the resistance towards carbon attack. The adhesion of -Al 2 O 3 (0001)/ -NiAl was investigated by DFT in a study by Carling and Carter [28].…”

Section: Introductionmentioning

confidence: 99%

First-principles investigations of Ni3Al(111) and NiAl(110) surfaces at metal dusting conditions

et al. 2011

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We investigate the structure and surface composition of the -Ni 3 Al(111) and -NiAl(110) alloy surfaces at conditions relevant for metal dusting corrosion related to catalytic steam reforming of natural gas. In regular service as protective coatings, nickel-aluminum alloys are protected by an oxide scale, but in case of oxide scale spallation, the alloy surface may be directly exposed to the reactive gas environment and vulnerable to metal dusting. By means of density functional theory and thermochemical calculations for both the Ni 3 Al and NiAl surfaces, the conditions under which C O and O H adsorption is to be expected and under which it is inhibited, are mapped out. Because C O and O H are regarded as precursors for nucleating graphite or oxide on the surfaces, phase diagrams for the surfaces provide a simple description of their stability. Specifically, this study shows how the C O and O H coverages depend on the steam to carbon ratio (S/C) in the gas and thereby provide a ranking of the carbon limits on the different surface phases.

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Section: Introductionmentioning

confidence: 99%

First-principles investigations of Ni3Al(111) and NiAl(110) surfaces at metal dusting conditions

et al. 2011

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“…2), the adhesion energy drops precipitously (W sep ∼ 0.18 J∕m 2 ) (17), confirming similar findings by Zhang et al (28) for an Nið111Þ∕Al 2 O 3 interface. This direct and dramatic decrease in adhesion is due to electron-pair-electron-pair repulsions between S atoms and O 2− ions in alumina, which prevent formation of covalent bonds across the interface (17). The weakened adhesion and a spatial gap that develops at the interface helps explain Auger electron spectroscopy and electron microscopy measurements on TBCs that find S present near voids between the bond coat alloy and the oxide.…”

Section: Resultsmentioning

confidence: 86%

“…Electron pair repulsions between the nearly filled 2p shell of the O anions and the nearly filled 3d shell of the Ni atoms are responsible for the very weak adhesion at the TGO/BC interface. In fact, the only useful crossinterface bonding was found to involve metal-metal interactions between the Ni in the BC and the Al cations in the TGO (17). The oxygen anions only destabilized the interface.…”

Section: Resultsmentioning

confidence: 98%

“…We therefore concluded that Pt does not directly increase interface adhesion. Its beneficial role must involve affecting other processes, possibly modifying diffusion processes in the TBC or preventing S segregation to the interface (17). In retrospect, and based on our earlier insights about why the alumina∕Ni interface is weak, it seems obvious that Pt should not improve TBC adhesion directly: It has a nearly filled d shell like Ni and therefore cannot form strong bonds to oxygen.…”

Section: Resultsmentioning

confidence: 99%

“…Early on we evaluated the work of separation (W sep ) for bulk zirconia phases (13) and α-Al 2 O 3 (14), as well as for models of the relevant heterogeneous interfaces, YSZ/TGO (15) and TGO/BC (16,17). This series of calculations quantified that the weak links are the interfaces, with the latter being weakest of all.…”

Section: Resultsmentioning

confidence: 99%

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Atomic-scale insight and design principles for turbine engine thermal barrier coatings from theory

Marino

Hinnemann

Carter

2011

Proc. Natl. Acad. Sci. U.S.A.

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To maximize energy efficiency, gas turbine engines used in airplanes and for power generation operate at very high temperatures, even above the melting point of the metal alloys from which they are comprised. This feat is accomplished in part via the deposition of a multilayer, multicomponent thermal barrier coating (TBC), which lasts up to approximately 40,000 h before failing. Understanding failure mechanisms can aid in designing circumvention strategies. We review results of quantum mechanics calculations used to test hypotheses about impurities that harm TBCs and transition metal (TM) additives that render TBCs more robust. In particular, we discovered a number of roles that Pt and early TMs such as Hf and Y additives play in extending the lifetime of TBCs. Fundamental insight into the nature of the bonding created by such additives and its effect on high-temperature evolution of the TBCs led to design principles that can be used to create materials for even more efficient engines.A ircraft and power plants share a common source of usable energy: Both employ turbine engines that combust fuel to either propel airplanes or produce electricity. At a time in which efficient use of energy is paramount, improving the efficiency of turbine engines is one means to contribute to this global challenge. Turbine engines operate via the Brayton cycle, which offers lower carbon dioxide emissions and lower cost for power generation than other possible alternatives. Their efficiency can be increased by increasing the inlet temperature, which allows more expansion of gas that creates more pressure to drive the turbine. However, high-temperature operation, under oxidizing conditions, poses serious demands on the materials used to construct jet engine components. Materials must be found that are robust under such harsh operating conditions. Engineers over the past few decades have improved greatly the thermomechanical properties of the metal alloy comprising, e.g., the turbine blades, and have created a multilayer coating for the blades that protects against both heat and corrosion, referred to as a thermal barrier coating (TBC). These materials advances, along with internal component cooling, have been astonishingly successful, allowing the gas temperature to exceed the melting point of the metal alloy from which the engine components are constructed! Despite these advances, more robust TBCs are desired, either to extend TBC service lifetime under present-day operating conditions or to operate at even higher temperatures to achieve more efficient energy conversion. As a result, characterization and optimization of TBC properties have continued to be active areas of research. As is the case for most materials development, the usual path to improve TBCs relies on trial and error. Many materials compositions are fabricated, characterized, and tested. Unfortunately, characterization typically is performed postmortem, as virtually no instruments exist to characterize a TBC in situ during operation. The lack of in situ probes makes...

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Oxidation‐Induced Stresses in Thermal Barrier Coating Systems

Evans¹

2010

Advanced Ceramic Coatings and Interfaces V

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Effects of segregating elements on the adhesive strength and structure of the α-Al2O3/β-NiAl interface

Cited by 101 publications

References 47 publications

First-principles investigations of Ni3Al(111) and NiAl(110) surfaces at metal dusting conditions

First-principles investigations of Ni3Al(111) and NiAl(110) surfaces at metal dusting conditions

Atomic-scale insight and design principles for turbine engine thermal barrier coatings from theory

Oxidation‐Induced Stresses in Thermal Barrier Coating Systems

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