Neutron methods link microstructure to processing and performance for thermal barrier coatings. (News Briefs).Although coatings are used in the electric utility and aircraft industries to protect advanced gas turbines from increasingly high operating temperatures, there is presently no single industrial technique that can quantify the component void microstructures that control thermal barrier coating Thermal barrier coatings are highly advanced material systems applied to metallic surfaces, such as gas turbine or aero-engine parts, operating at elevated temperatures. These coatings serve to insulate metallic components from large and prolonged heat loads by utilizing thermally performance and reliability. NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. researchers have developed advanced small-angle neutron and x-ray scattering methods which, with appropriate models, provide a microstructure characterization for thick, free-standing material. Two innovations now extend these studies to submillimeter-thick coatings in situ on the substrate, and suggest that such characterization can provide calibration and validation of the partial information available from other methods. In near-surface small-angle neutron scattering Small angle neutron scattering (SANS) is a laboratory technique, similar to the often complementary techniques of small angle X-ray scattering (SAXS) and light scattering. These are particularly useful because of the dramatic increase in forward scattering that occurs at phase (NS-SANS), reflection geometry is used to determine apparent internal void surface area distributions within thermal barrier coatings to typical mean depths of 0.1 mm. The method has been used to study the effects of thermal cycling on an yttria-stabilized zirconia plasma sprayed thermal barrier coatings deposited on a nickel superalloy su·per·al·loy n. Any of several complex temperature-resistant alloys. substrate. The NS-SANS measurement has revealed a marked increase in intra-splat cracking perpendicular to the substrate, arising from thermal mismatch strains between the coating and the substrate. This effect contrasts with a preferential sintering sintering, process of forming objects from a metal powder by heating the powder at a temperature below its melting point. In the production of small metal objects it is often not practical to cast them. of intra-splat cracks for free-standing deposits and it significantly modifies the properties and performance of thermal barrier coatings subjected to elevated service temperatures. For 0.3 mm to 0.4 mm thick thermal barrier coatings on substrates, microstructures can also be determined using a modified form of ultra-small-angle x-ray scattering (USAXS), suitable for the study of anisotropic Refers to properties that differ based on the direction that is measured. For example, an anisotropic antenna is a directional antenna; the power level is not the same in all directions. Contrast with isotropic. materials. It has been applied to thermal barrier coatings fabricated by plasma spray and by electron-beam physical vapor deposition  This article or section is in need of attention from an expert on the subject.Please help recruit one or [ improve this article] yourself. See the talk page for details. . By combining conventional SANS studies of freestanding thermal barrier coating microstructures with NS-SANS and anisotropic USAXS studies of the modifications introduced when the thermal barrier coating is in situ on the substrate, a valuable validation tool is becoming available to support industrial thermal barrier coating design. CONTACT: Andrew Allen, (301) 975-5982; andrew.allen@nist.gov. |
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