High‐Resolution Transmission Electron Microscopy Studies of a Near Σ11 Grain Boundary in α‐Alumina

Höche, Thomas; Kenway, Philip R.; Kleebe, Hans‐Joachim; Rühle, M.; Morris, Patricia A.

doi:10.1111/j.1151-2916.1994.tb07001.x

Cited by 74 publications

(28 citation statements)

References 31 publications

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“…A number of papers have been reported for bicrystal experiments to investigate the grain boundary energy, [5][6][7][8][9] atomic structure, [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] grain boundary sliding [27][28][29][30][31][32][33][34][35] and so on. Although most of them focused on metals, and some papers have reported for ceramics.…”

Section: Introductionmentioning

confidence: 99%

Grain Boundary Sliding and Atomic Structures in Alumina Bicrystals with [0001] Symmetric Tilt Grain Boundaries

et al. 2002

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Orientation controlled alumina bicrystals were fabricated by a hot joining technique at 1773 K in air to obtain [0001] symmetric tilt boundaries including coincidence grain boundaries. The grain boundary energies were measured by the thermal grooving technique, and they were found to strongly depend on the grain boundary character. Atomic structures of those grain boundaries were observed by high-resolution electron microscopy (HREM). It was found that the atomic structures did not always correlate with the grain boundary energies. This finding indicates that the grain boundary energy originates not only from the atomic bonding on the grain boundary but also from the strain of the grain interior in the vicinity of the boundary. The grain boundary sliding was also investigated by the high-temperature creep test. As the results, the grain boundaries with the same energy showed different sliding behavior. The occurrence of grain boundary sliding is considered to depend on the atomic bonding of a grain boundary.

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Section: Introductionmentioning

confidence: 99%

Grain Boundary Sliding and Atomic Structures in Alumina Bicrystals with [0001] Symmetric Tilt Grain Boundaries

et al. 2002

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“…Of the many GBs formed in α-Al 2 O 3 , we chose the Σ11 tilt GB-the subject of previous experimental (35) and theoretical (36)(37)(38) work-to test our findings. A detailed scan of possible translations parallel to the GB interface revealed a previously undescribed structure (39) for the clean GB that is lower in energy than previously proposed structures based on transmission electron microscope (TEM) data and classical potential simulations (36).…”

Section: Resultsmentioning

confidence: 99%

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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“…The composition and structure of A1203 surfaces and interfaces have been the topic of numerous studies and are found to be strongly dependent upon the ambient environment [3,16,[38][39][40][41][42][43][44][45]. In conditions of high oxygen partial pressure, most surfaces are believed to be oxygen terminated.…”

Section: Introductionmentioning

confidence: 99%

“…Atomic transport and interface energy are clearly related to defect chemistry but a correlation between the detailed atomic structure, the chemical bonding, the stoichiometry, cation disorder, and impurity solute segregation is still poorly understood because of the difficulty of getting informative data. Chiang and co-workers [10,11] have shown there to be a strong influence of chemical composition and space charge on the grain boundary mobility of magnesium aluminate spinels during heat treatments and a number of groups (for example [3,[12][13][14][15][16][17][18][19]) have paid attention to elucidating the detailed atomic structures at various ceramic-oxide interfaces and grain boundaries. In particular, Li et al [20] have recently described the atomic structure of the magnèsium aluminate/sapphire boundary formed between a MgO / Alz 03 couple by a solid state interdiffusion process that had been activated by the irradiation of the electron microscope.…”

Section: Introductionmentioning

confidence: 99%

Spectrum-Line Profile Analysis of a Magnesium Aluminate Spinel Sapphire Interface

Bruley

Tseng

Williams

1995

Microsc. Microanal. Microstruct.

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Abstract. 2014 Spatially resolved chemical composition and spectroscopic line profiles have been gathered from the space charge region across a spinel/sapphire interface using a dedicated scanning transmission electron microscope. The electron energy-loss spectra reveal an excess of Mg (relative to stoichiometric spinel) along with Cr segregated to the interfacial zone. A quantitative least squares decomposition of a spectrum-line profile of the Al L2, 3 absorption edge fine structures into two standard components clearly highlights the transition from sapphire into spinel; further analysis indicates that the degree of site inversion, which is the fractional occupancy of tetrahedral sites by trivalent Al, increases within 5 nm of the boundary. The overall charge neutrality at the interface is maintained by the increased concentration of negative charge, probably interstitial O anions which are also present in excess quantity relative to stoichiometric spinel and sapphire.

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High‐Resolution Transmission Electron Microscopy Studies of a Near Σ11 Grain Boundary in α‐Alumina

Cited by 74 publications

References 31 publications

Grain Boundary Sliding and Atomic Structures in Alumina Bicrystals with [0001] Symmetric Tilt Grain Boundaries

Grain Boundary Sliding and Atomic Structures in Alumina Bicrystals with [0001] Symmetric Tilt Grain Boundaries

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

Spectrum-Line Profile Analysis of a Magnesium Aluminate Spinel Sapphire Interface

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