The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Philippe Lours - One of the best experts on this subject based on the ideXlab platform.
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Spallation Process of Thermally Grown Oxides by In-Situ CCD Monitoring Technique
Journal of Iron and Steel Research International, 2009Co-Authors: Qi Yu-hong, Philippe Lours, Yannick Le MaoultAbstract:In cooling process of Fe-Cr-Al alloy oxidized at 1 300 degrees C, the effect of cooling speed and exposure time on oxide spalled area fraction and successive variety of the spalled region were studied by investigating evolvement of the thermally grown oxide using in-situ CCD monitoring technique. The results showed that oxide Spallation can be restrained by controlling cooling speed and the critical temperature drop of Spallation initiation which is closely related to the oxide thickness or exposure time, and the-Spallation process of a little region may be described in more detail as two routes: from the oxide/substrate interface micro-decohesion, micro-buckles, buckle spreading, buckle crack to Spallation and from the interface micro-decohesion, micro-buckles, buckle crack and Spallation to the residual oxide decohesion and Spallation.
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Spallation Process of Thermally Grown Oxides by In-Situ CCD Monitoring Technique
Journal of Iron and Steel Research International, 2009Co-Authors: Philippe Lours, Yannick Le MaoultAbstract:Abstract In cooling process of Fe-Cr-Al alloy oxidized at 1 300 °C, the effect of cooling speed and exposure time on oxide spalled area fraction and successive variety of the spalled region were studied by investigating evolvement of the thermally grown oxide using in-situ CCD monitoring technique. The results showed that oxide Spallation can be restrained by controlling cooling speed and the critical temperature drop of Spallation initiation which is closely related to the oxide thickness or exposure time, and the Spallation process of a little region may be described in more detail as two routes: from the oxide/substrate interface micro-decohesion, micro-buckles, buckle spreading, buckle crack to Spallation and from the interface micro-decohesion, micro-buckles, buckle crack and Spallation to the residual oxide decohesion and Spallation.
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Direct obervations and analysis of the Spallation of alumina scales grown on PM2000 alloy
MATERIALS SCIENCE AND ENGINEERING. A STRUCTURAL MATERIALS, 2008Co-Authors: Philippe Lours, Yannick Le Maoult, Julien Sniezewski, Bernard PieraggiAbstract:The Spallation during cooling or thermal cycling of alumina scales grown at high temperature on PM2000 alloy is directly observed and recorded using CCD cameras. This simple and direct method permits to determine easily and accurately the scale Spallation kinetics. In addition, it provides many insights on the Spallation mechanisms and processes and their evolution as well as on the effect of substrate microstructure on Spallation.
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Direct observations and analysis of the Spallation of alumina scales grown on PM2000 alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007Co-Authors: Philippe Lours, Yannick Le Maoult, Julien Sniezewski, Bernard PieraggiAbstract:The Spallation during cooling or thermal cycling of alumina scales grown at high temperature on PM2000 alloy is directly observed and recorded using CCD cameras. This simple and direct method permits to determine easily and accurately the scale Spallation kinetics. In addition, it provides many insights on the Spallation mechanisms and processes and their evolution as well as on the effect of substrate microstructure on Spallation.
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Oxidation and oxide Spallation of heat resistant cast steels for superplastic forming dies
Materials Science and Engineering: A, 2002Co-Authors: Stéphane Baleix, Gérard Bernhart, Philippe LoursAbstract:The oxidation and oxide Spallation behaviour of austenitic and ferritic heat resistant cast steels used for manufacturing superplastic forming dies is investigated in isothermal and cyclic conditions. Gravimetric, microstructural and mechanical approaches are utilised to address the oxidation and Spallation kinetics, to determine the nature of oxides grown at the surface of the materials and to discriminate the different routes to Spallation depending on the substrate metallurgical structure and the oxidation conditions. It is shown that both types of material develop similar oxide scales with similar kinetics. The ferritic alloys appear to be more resistant to oxide Spallation than the austenic alloys. The decrease of the fracture energy at the interface substrate/oxide during oxidation resulting from an aggregation of interfacial defects, causes Spallation by wedging and buckling for thin and thick oxide layers, respectively.
Rizhi Wang - One of the best experts on this subject based on the ideXlab platform.
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Fracture Behavior of Diamond-like Carbon Films on Stainless Steel Under a Micro-tensile Test Condition
Diamond and Related Materials, 2006Co-Authors: Heon Woong Choi, Kwang-ryeol Lee, Rizhi WangAbstract:We investigated the stability of the DLC film coated on 304 stainless steel substrate by r.f. PACVD method. Fracture and Spallation behaviors of the coating were observed during micro-tensile test of the film/substrate composite. As the tensile deformation proceeded, the cracks of the film appeared in the perpendicular direction to the tensile axis. Further deformation resulting in the local necking with shear band of 55° inclined to the tensile axis, induced the Spallation of the film, which was initiated at the cracks of the film, and was aligned along the slip directions. We found that both the cracking and the Spallation behaviors are strongly dependent on the pretreatment condition, such as Ar plasma pretreatment or Si buffer layer deposition. The Spallation of the film was significantly suppressed in an optimized condition of the substrate cleaning by Ar glow discharge. These results show that the Spallation behavior during the tensile test can be used to estimate the interfacial strength of the coating with relatively poor adhesion.
Yanhong Wei - One of the best experts on this subject based on the ideXlab platform.
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Finite element analysis of anti-Spallation thermal barrier coatings
Surface and Coatings Technology, 2003Co-Authors: Aiguo Liu, Yanhong WeiAbstract:Unpredictable failure due to delamination and Spallation of thermal barrier coating (TBC) systems used in hot parts of aircraft engines limits their service lifetime. Research in recent years has suggested that the residual stresses in the TBC system were affected by the presence of the thermally grown oxide (TGO) and which causes the Spallation. A new idea to improve the anti-Spallation character of the TBC system by applying an anti-Spallation layer was presented in the current study and the stress distribution in TBCs produced with and without this layer was analyzed using the finite element method. The results show that the stress-state can be improved by the introduction of an additional anti-Spallation layer on top of the partially stabilized zirconia (PSZ). The ultra high tensile stress after heating and compressive stress after cooling could be reduced from several GPa to several hundreds MPa or less. The stress perpendicular to the interface was also reduced. This would minimize the tendency of crack initiation on the interface, and hence the tendency of delamination and Spallation of the TBC system.
J. B. Gnanamoorthy - One of the best experts on this subject based on the ideXlab platform.
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Synergistic influence of alloy grain size and Si content on the oxidation behavior of 9Cr−1Mo steel
Oxidation of Metals, 1994Co-Authors: R.k. Singh Raman, J. B. Gnanamoorthy, S. K. RoyAbstract:The synergistic influence of prior-austenite grain size and silicon content of 9Cr−1Mo steel on the resistance to scale Spallation has been studied in air at 773 K (for 500 hr) and 973 K (12 hr). Two steels, irrespective of their grain size and Si content, did not show Spallation during oxidation at 773 K. Spallation occurred at 973 K, and fine-grain steels exhibited less Spallation resistance than coarse-grain ones (in low-as well as high-Si steels). Among the four possible combinations of grain size ans Si content, the steel with low Si and fine grains showed least resistance to Spallation, while the steel with high Si and coarse grains showed the best resistance. Spallation was found to initiate in the areas adjoining the oxide ridges formed at the alloy grain boundaries. Oxide scales at the ridges and within the grains were analyzed by scanning electron microscopy (SEM/EDX) and secondary-ion mass spectrometry (SIMS). These analyses suggest depletion of silicon from the areas adjoining grain boundaries, resulting in thicker scaling that triggers Spallation in such areas. For similar grain-size materials, the necessary thickness for Spallation was attained earlier with low-Si steel rather than in high-Si steel.
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Influence of prior-austenite grain size on the oxidation behavior of 9 wt.% cr-1 wt.% Mo steel
Oxidation of Metals, 1992Co-Authors: R.k. Singh Raman, J. B. GnanamoorthyAbstract:The effect of grain size on the oxidation of 9 wt.% Cr-1 wt.% Mo steel (with prior-austenite grain sizes of 90, 210, and 360 μm) has been studied at 973 K in air. After the initial stages of oxidation (up to 60 min), the fine-grain specimen (90 μm) suffered heavy Spallation. A similar Spallation took place after 120 min in the case of the specimen with intermediate grain size (210 μm), and after 360 min in a coarse-grain (360 μm) specimen. This increase in the duration for the onset of pronounced Spallation with grain size has been attributed to the smaller area of the grain boundaries which are the locations of higher growth stresses leading to Spallation. This dependence of Spallation characteristics on the alloy grain size has been confirmed by the incidence of higher acoustic-emission activity during AE monitoring. Scanning electron microscopy (SEM) has confirmed the occurrence of pronounced Spallation of the oxides formed in the areas adjoining the grain boundaries.
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influence of prior austenite grain size on the oxidation behavior of 9 wt cr 1 wt mo steel
Oxidation of Metals, 1992Co-Authors: R Singh K Raman, J. B. GnanamoorthyAbstract:The effect of grain size on the oxidation of 9 wt.% Cr-1 wt.% Mo steel (with prior-austenite grain sizes of 90, 210, and 360 μm) has been studied at 973 K in air. After the initial stages of oxidation (up to 60 min), the fine-grain specimen (90 μm) suffered heavy Spallation. A similar Spallation took place after 120 min in the case of the specimen with intermediate grain size (210 μm), and after 360 min in a coarse-grain (360 μm) specimen. This increase in the duration for the onset of pronounced Spallation with grain size has been attributed to the smaller area of the grain boundaries which are the locations of higher growth stresses leading to Spallation. This dependence of Spallation characteristics on the alloy grain size has been confirmed by the incidence of higher acoustic-emission activity during AE monitoring. Scanning electron microscopy (SEM) has confirmed the occurrence of pronounced Spallation of the oxides formed in the areas adjoining the grain boundaries.
Frank W. Zok - One of the best experts on this subject based on the ideXlab platform.
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transition from penetration cracking to Spallation in environmental barrier coatings on ceramic composites
Surface & Coatings Technology, 2019Co-Authors: William D Summers, Matthew R. Begley, Frank W. ZokAbstract:Abstract The article addresses the competition between driving forces for penetration cracking and for Spallation in bilayer environmental barrier coatings on SiC-based composites. Coatings of interest consist of an outer rare-earth monosilicate (MS) and an inner rare-earth disilicate (DS). Finite element analysis is used to compute energy release rates (ERR) for cracking as functions of misfit strains, layer thicknesses and size of putative cracks. The results indicate that, for certain property combinations, ERRs for Spallation in the DS layer exceed those for continued penetration. The implication is that penetration cracks could branch and cause coating Spallation. A case study comparing bilayers of Yb- and Y-silicates reveals domains in which (i) the tolerable thickness of MS is high, but eventual Spallation could potentially remove the entire DS coating along with the adjoining MS, and (ii) the tolerable thickness of MS is low, but, if it were to occur, Spallation would follow a path near the MS/DS interface, leaving most of the DS intact. The behaviors prove to be sensitive to the thermal expansion coefficient of the underlying composite, even over the rather narrow range of values typical of SiC-based composites.
