A5037373736- High-Temperature Coating Behaviors
- Intermetallics and Advanced Alloy Properties
- Nuclear Materials and Properties
- Catalytic Processes in Materials Science
- Advanced ceramic materials synthesis
- Microstructure and mechanical properties
- Nuclear materials and radiation effects
- High-Velocity Impact and Material Behavior
- High Temperature Alloys and Creep
- Metal and Thin Film Mechanics
- Fatigue and fracture mechanics
- Luminescence Properties of Advanced Materials
- Glass properties and applications
- Advanced materials and composites
- Recycling and utilization of industrial and municipal waste in materials production
- Numerical methods in engineering
- Advancements in Solid Oxide Fuel Cells
- Force Microscopy Techniques and Applications
- Semiconductor materials and devices
- Nonlocal and gradient elasticity in micro/nano structures
- Tribology and Lubrication Engineering
- Pigment Synthesis and Properties
- Engineering Applied Research
- Diamond and Carbon-based Materials Research
- Ultrasonics and Acoustic Wave Propagation
GE Global Research (United States)
2010-2017
General Electric (United States)
1997-2017
Harvard University Press
2012
University of California, Santa Barbara
1995-1998
American Ceramic Society
1997
University of Trieste
1997
The stresses in the aluminum oxide formed during high-temperature oxidation of a bond-coated superalloy are shown to be measurable through zirconia thermal barrier coatings. basis for measurements is piezospectroscopic shift R-line fluorescence (photoluminescence) from Cr3+ impurities incorporated into growing scale. Measurements coating feasible because (partially stabilized) coatings have some transparency at both excitation and frequencies.
The temperature capability of yttria‐stabilized zirconia thermal barrier coatings (TBCs) is ultimately tied to the rate evolution “nontransformable” t ′ phase into a depleted tetragonal form predisposed monoclinic transformation on cooling. phase, however, has been shown decompose in small fraction time necessary phase. Instead, modulated microstructure consisting coherent array Y‐rich and Y‐lean lamellar phases develops early process, with mechanistic features suggestive spinodal...
The relationship between yttria concentration and the unit cell parameters in partially fully stabilized zirconia has been reassessed, motivated by need to improve accuracy of phase analysis upon decomposition t′ ‐based thermal barrier coatings. Compositions ranging from 6 18 mol% YO 1.5 were synthesized examined means high‐resolution X‐ray diffraction. Lattice determined using Rietveld refinement method, a whole‐pattern fitting procedure. revised empirical relationships fall within range...
Phase evolution accompanying the isothermal aging of free‐standing air‐plasma sprayed ( APS ) 7–8 wt% yttria‐stabilized zirconia (8 YSZ thermal barrier coatings TBC s) is described. Aging was carried out at temperatures ranging from 982°C to 1482°C in air. The high‐temperature kinetics phase metastable t′ into a mixture transformable Y‐rich (cubic) and Y‐lean (tetragonal) phases are documented through ambient temperature X‐ray diffraction XRD characterization. A Hollomon–Jaffe parameter...
An analytical model is presented to describe the influence of sample-probe interactions on shape spectroscopic lines. By considering discrete sampling spatial property variations using a focused probe, predicts gradient-induced line broadening, as well probe channeling near free surfaces. The magnitude governed by two system parameters: size and gradient. Furthermore, certain heterogeneities are found contribute appreciably signal its associated over distances several times size....
The correlation between microstructural and phase evolution in aged, yttria‐partially‐stabilized zirconia, air plasma‐sprayed coatings is discussed. Freestanding with the dense, vertically cracked structure were isothermally aged at 1482°C (2700°F) air. Characterization of resulting microstructures was conducted using transmission electron microscopy, then compared a parallel analysis via synchrotron X ‐ray diffraction ( XRD ) described Part I. Additional context provided by related studies...
During the early stages of oxidation (111) NiAl at 1100 °C, an alumina scale forms and undergoes a series allotropic phase transformations. In final development, metastable Θ-alumina transforms to equilibrium α-alumina phase. Images formed using photoluminescence from trace Cr3+ impurities in scale, conjunction with scanning electron microscopy, indicate that by nucleation growth process within matrix. Lateral impingement growing islands coincides reported drop kinetics those characteristic...
Continuum concepts are used to evaluate the competition between crack advance and dislocation nucleation at tip of a having finite curvature. The analysis reveals that favorability propagation versus emission depends upon bluntness tip. One implication is may initially emit dislocations only reinitiate cleavage reaching sufficiently blunted geometry. present framework classify crystals as intrinsically ductile or brittle in terms unstable stacking energy, surface peak cohesive stresses...
The mechanisms of phase destabilization upon aging the metastable t′ yttria‐stabilized zirconia ( YSZ ) are poorly understood, despite its broad application in thermal barrier coatings. To provide insight, synchrotron X‐ray diffraction XRD with a quadrupole lamp furnace is used to examine temperature response, including expansion and evolution, 9 mol% (8 wt%) YO 1.5 t′‐ 8 . equilibrated powders ranging from 0 18.4 also investigated better understand effect composition on anisotropy. T c/t...
Abstract We invoke the Lifshitz theory of van der Waals forces to derive a simple, analytical expression for adhesion across planar metal-ceramic interface. The energy is conveniently expressed as function readily accessible bulk properties respective materials. Application several non-reactive metal-sapphire systems shows predicted provide good lower-bound estimate measured energy. Apart from platinum and palladium, where strong metal-aluminium interactions have been predicted, energies in...
Using the technique of fluorescence piezospectroscopy, we determine distribution thermal residual stresses across edges three laminated alumina/zirconia composites. We develop a methodology for separating measured stress state into microstresses that result from grain‐to‐grain mismatch and macrostresses lamination‐induced between individual plies. Comparison edge‐stress distributions those calculated based on simple force‐superposition model shows good agreement, indicating laminate system...
Characteristic photostimulated luminescence (fluorescence) in the visible range is reported from theta transition alumina prepared by using a variety of methods. The associated with trace concentrations chromium and can be intensified intentional doping. theta‐alumina similar to, albeit considerably weaker than, R‐line alpha‐alumina. spectrum characterized doublet at ∼14575 14645 cm −1 77 K blue‐shifted R‐lines alpha‐alumina ∼150 . attributed to Cr 3+ ions octahedral coordination used for...
A systematic study of factors affecting the delamination energy release rate and mode mix a thermal barrier coating attached to substrate is presented accounting for influence gradients combined with rapid hot surface cooling. Transient induce stress through substrate, which produce overall bending if not very thick it constrained. Due their influences on stresses, thickness constraint are important aspects mechanics coating-substrate systems, must be considered when laboratory tests...
Abstract Under the sponsorship of U.S. National Science Foundation, a workshop on emerging research opportunities in ceramic and glass science was held September 2016. Reported here are proceedings workshop. The report details eight challenges identified through discussions: Ceramic processing: Programmable design assembly; defect genome: Understanding, characterizing, predicting defects across time length scales; Functionalizing for unprecedented properties; flatlands: Defining...