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  • 1
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 345-346 (Aug. 2007), p. 1035-1038 
    ISSN: 1013-9826
    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: Thermal barrier coating (TBC) of a gas turbine blade suffers from high temperatureoxidation. It is known that thermally growth oxidation (TGO) grows at the interface between ZrO2-8%Y2O3 and CoNiCrAlY, and the TGO degrades the adhesive strength. The purpose of this study isto clarify the TGO growth process. Thermal aging tests of ZrO2-8%Y2O3 / CoNiCrAlY TBCsystems under various temperature conditions were carried out. TGO growth process was observedby an electron probe micro analyzer (EPMA). Both TGO of Al and TGO of other elements wereexamined, and the thickness of the TGOs were examined. Results are summarized as follows. (1)The delamination occurred at a ZrO2-8%Y2O3 layer beside the interface. (2) The growth rate ofcomplicated TGO which consisted of Co, Ni and Cr increased with an increase of temperature.However, the complicated TGO wasn’t related with the delamination life. (3) The delaminationcould occur if the thickness of Al TGO increased more than about 3 μm
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 261-263 (Apr. 2004), p. 453-458 
    ISSN: 1013-9826
    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: A surface strain measurement approach to understanding of delamination processes of thermal barrier coatings (TBCs) under heat cycle conditions was described in this paper. Heat cycle tests between the high temperature ranged from 1473K to 1073K and the relatively low temperature (573K) was carried out on thermal barrier coated type 304 stainless steel specimens. 8mass%Y〈sub〉〈/sub〉2O〈sub〉〈/sub〉3-ZrO〈sub〉〈/sub〉2 and Al〈sub〉〈/sub〉2O〈sub〉〈/sub〉3 coatings were used for the TBCs. The surface strain behavior during the heat cycle test was measured using a laser speckle strain/displacement gauge (SSDG). It was found that the thermal expansion of a substrate was almost reflected on a surface strain if a delamination wasn't initiated, while the value of a surface strain decreased to the value of the thermal expansion of a ceramics-coating if the delamination of the ceramics-coating was initiated. The state of a subsurface delamination was able to be nondestructively inferred by the surface strain behavior. The delamination life of a ceramics-coating in the specimen with a low-pressure-plasma-sprayed (LPPS)bond-coating was found to be longer than that with an atmospheric-plasma-sprayed (APS) bond-coating. The large roughness of a bond-coating was also found to be effective in improving the delamination life of a ceramics-coating owing to the restriction of a crack propagation parallel to the interface between the ceramics-coating and the bond-coating
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 353-358 (Sept. 2007), p. 495-498 
    ISSN: 1013-9826
    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: Plasma sprayed CoNiCrAlY coating can prevent oxidation and corrosion of turbine bladesin a gas turbine plant. Cracking and delamination of coatings are affected by the residual stresses inthe coatings. In this study, the arising mechanism of residual stress in the plasma sprayed coating wasdiscussed. The residual stresses in CoNiCrAlY coatings were measured by X-ray diffraction method.The coatings were deposited by either low pressure plasma spraying (LPPS) or atmospheric plasmaspraying (APS). Each elastic constant which was used for determining the X-ray stress constant wasmechanically measured by a bending test. Two kinds of substrates were prepared for each coating inorder to examine the effect of thermal expansion coefficient of a substrate. Results were as follows.The residual stresses of the coatings on steel substrates were tensile. On the other hand, the residualstresses on stainless substrates were lower than those on steel substrates. Arising mechanism of theresidual stresses can be explained by both the linear expansion coefficient and the range of changingtemperature. It was also found that the absolute residual stresses were affected by the spraying powdersize and increased with a decrease of the spraying powder size. It was principally caused by thedifference in the elastic constants
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 306-308 (Mar. 2006), p. 387-392 
    ISSN: 1013-9826
    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: Thermal barrier coating (TBC) on the element for high temperature service, such as a gas turbine blade, has become an indispensable technology. In this study, adhesive strengths of plasmasprayed CoNiCrAlY coatings were examined using an indentation method. In order to examine the effects of the spraying process on the adhesive strength of a sprayed coating, coatings were deposited by both atmospheric plasma spraying (APS) and low pressure plasma spraying (LPPS). The half number of CoNiCrAlY(LPPS) specimens were thermally aged for diffusion treatment. The load-displacement curves during the indentation were measured, and the delamination energy per unit area of delamination was estimated. The delamination load was high when the distance from an edge of a specimen was long, however the energy per unit delamination area was almost independent of the distance from the edge and was uniquely determined. The delamination energy of CoNiCrAlY(APS) and CoNiCrAlY(LPPS) coatings were found to be approximately the same. The delamination energy of CoNiCrAlY(LPPS) with diffusion thermal treatment was widely scattered as compared with foregoing two coatings, however the energy of the CoNiCrAlY(LPPS) coating with diffusion thermal treatment was found to be about three times higher than those of bothCoNiCrAlY(APS) and CoNiCrAlY(LPPS) coatings. It was concluded that diffusion thermal treatment was effective in improving the delamination strength. The CoNiCrAlY(LPPS) coating with diffusion thermal treatment was also found to be effective in improving the fatigue fracture life of a thermal-barrier-coated material
    Type of Medium: Electronic Resource
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