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  • 2005-2009  (4)
  • 1
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 595-598 (Sept. 2008), p. 77-85 
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Ceramic Thermal Barrier Coatings (TBCs) have been developed for advanced gas turbineengine components to improve the engine efficiency and reliability. The integrity and reliability ofthese coatings is of paramount importance. Accurate prediction of service lifetimes for thesecomponents relies upon many factors, and is not straightforward as knowledge of the serviceconditions and accurate input data for modelling are required. The main cause of failure of coatingsis through debonding which develops as a consequence of thermally induced strains between themetallic bondcoat and the alumina TGO layers due to the differences in the thermal expansioncoefficients of the individual layers. Thermal transients due to the power cycles of turbines will thencause these fractures to grow between the TGO and the bondcoat. When these fractures reach acritical size they can grow rapidly and cause the TBC to spall off. Thermal cycling of TBCs is usedtherefore to evaluate and rank TBC performance. Within the laboratory this is often conductedunder isothermal conditions. Whilst this test method has performed adequately in the past it doesnot fully simulate service conditions. Work has been underway therefore to develop a morecomplex test method, which better simulates the service conditions experienced by the TBC. Theapproach here employs a gas torch to heat the operating face of the TBC whilst cooling the rear ofthe substrate with compressed air, thereby imparting a heat flux on the specimen. The specimen isthen cycled by removing the gas torch and cooling with compressed air on the front and rear faces.Tests have been conducted on a TBC system consisting of an IN738 substrate with a CN334bondcoat and EBPVD TBC. Thermal cycling tests have been performed under both isothermal andheat flux conditions. During the course of the tests the samples were examined non-destructivelyusing a thermal camera to identify early indications of spallation. This paper reports on theperformance of the flame rig equipment and the results from the exposures on the TBC system
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Applied mechanics and materials Vol. 3-4 (Aug. 2006), p. 105-110 
    ISSN: 1662-7482
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Hole drilling is one of the most widely used techniques for measuring residual stress, but the conventional approach is limited in the near surface detail that can be resolved. Because of concerns about the levels of induced residual stress that might develop during machining and surface treatment processes, there is significant interest in developing a technique that can obtain near-surface residual stress information by the application of fine-increment hole drilling. Critical information can be lost if conventional, large depth increments are used and the fine incremental hole drilling approach, using depth increments as small as 20µm, offers a cost effective and rapid solution, with the possibility of measuring near surface stresses. Results focus on three different machining studies and a shot peened specimen, all cases where the stress field changes rapidly through the depth, particularly close to the surface. A systematic assessment of machining parameters is not within the scope of this paper and is not presented, but work has focused on highlighting the application and potential of the fine increment hole drilling approach
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 522-523 (Aug. 2006), p. 129-138 
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Three commercial martensitic steels have been oxidised in steam at 600 and 650 °C for times up to10000 h. The partition of minor elements within the oxide scales has been determined. Siliconforms an additional oxide layer beneath the spinel. Chromium, molybdenum and tungstenconcentrate in the spinel and manganese is present in both the spinel and magnetite. Severalproposed mechanisms for steam oxidation have been examined to explain the observed effects ofalloy composition. Modification of the oxide defect structure and oxidant gas penetration throughmicrocracks were identified as the mechanisms most able to explain the influence of alloycomposition
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 524-525 (Sept. 2006), p. 531-537 
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Hole drilling along with X-Ray diffraction, is one of the most widely used techniques formeasuring residual stress, but the conventional approach is limited in the near surface detail that canbe resolved. Because of concerns regarding the levels of induced residual stress that might developduring machining and surface treatment processes, there is significant interest in developing atechnique that can obtain near surface residual stress information by the application of fineincrement hole drilling. Through a cross comparison with X-ray diffraction and neutron diffractionthe procedure of fine incremental drilling has been validated, and the advantages of this techniquedemonstrated
    Type of Medium: Electronic Resource
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