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Jean Yves Guedou

Bio: Jean Yves Guedou is an academic researcher from Snecma. The author has contributed to research in topics: Thermal barrier coating & Superalloy. The author has an hindex of 4, co-authored 4 publications receiving 69 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the effects of net shape surfaces and surface conditioning have been investigated for static parts of aero-turboengines and space propulsion systems using HIPing of nickel base superalloys prealloyed powders.
Abstract: In order to reduce costs and increase the operating temperatures in aero-turboengines and space propulsion systems, net-shape or near net-shape production processes have been developed for static parts through HIPing (Hot Isostatic Pressing) of nickel base superalloys prealloyed powders. The presented results hereafter are related to the manufacturing processes and the mechanical properties (tensile, creep and LCF) characterisation. The effects of net shape surfaces and of surface conditioning have been investigated too. Examples of actual parts (CFM56 turbine casing and Vulcain rocket engine gas generator) illustrate the presentation. This study has confirmed the interest of this production route and future potential for development.

37 citations

Journal ArticleDOI
TL;DR: In this article, the LASAT-2D plots were used to evaluate the interface strength of EB-PVD thermal barrier coating (TBC) applied to turbine blades.
Abstract: The assessment of the interface strength of EB-PVD thermal barrier coating (TBC) is a key issue to control the production and better understand the ceramic spallation that will occur during life duration of coated turbine blades. The Laser Shock Adhesion Test (LASAT) involving bi-dimensional shock wave propagation, namely the LASAT-2D, consists in measuring the interfacial crack diameter when implementing a set of laser shocks with increased laser power densities. From the resulting “LASAT-2D plots”, adhesion strength could be obtained from tensile stress calculated at the interface with a finite element model of shockwave propagation combined to interface cracking criterion. This work is focusing on the qualitative approach to compare adhesion on TBC systems directly through LASAT-2D plots. Two different testing modes were investigated: the conventional MS mode when the laser irradiation is carried out on the metallic side of a TBC coupon and the newly developed CS mode for which the laser shock is implemented onto the ceramic side. The interfacial crack is revealed by the presence of a spot that could be measured on a top-view optical image of the ceramic. In this work, the actual relationship between spot diameter and interfacial inner crack size is clearly established for both MS and CS modes. It was achieved experimentally by examinations of SEM cross-sections or non-destructive piezospectroscopic measurements involving lifetime decay map of the photoluminescence signal. From LASAT-2D curves, the role of the laser conditions like laser shock diameter and substrate thickness is discussed. This discussion is illustrated through the results of the qualitative LASAT-2D method applied on two different TBC samples (as-coated and thermally-cycled). The final objective of this work is to enable a sound and relevant application of the LASAT on TBC systems for both modes. With this goal, the LASAT-2D CS was successfully applied directly on a TBC coated turbine blade.

31 citations

Journal ArticleDOI
TL;DR: In this article, a new protocol of LASAT has been introduced in order to measure the adhesion level of the ceramic coating from the exploitation of the two-dimensional effects that promote a shock wave pressure-dependent size of the damage.
Abstract: Damage prediction, adhesion strength and remaining lifetime of TBC are highly important data for understanding and preventing TBC spallation on blades. LAser Shock Adhesion Test (LASAT) is a powerful method to measure adhesion of coating due to its rapidity, simplicity and capabilities to distinguish different strength levels and the easy damage observation in case of TBCs. A new protocol of LASAT has been introduced in order to measure the adhesion level of the ceramic coating from the exploitation of the two-dimensional effects that promotes a shock wave pressure-dependent size of the damage. Finite element modeling, taking into account the TBCs dimensions, showed the edges effect on interfacial stress applied by laser shock.

6 citations

Journal ArticleDOI
TL;DR: In this article, secondary ion mass spectrometry (SISM) was used to study the sulfur distribution and its evolution after isothermal oxidation using a Ni-based single-crystal superalloy with a (Ni,Pt)Al bond coat.
Abstract: Sulfur distribution and its evolution after isothermal oxidation have been studied using secondary ion mass spectrometry. In this work, the systems consist of a Ni-based single-crystal superalloy with a (Ni,Pt)Al bond coat. Two superalloys are compared: AM1 and MCNG. The latter contains Hf as a reactive element. Isothermal oxidations are performed at 1,100 °C under synthetic air for 1, 10, 50, 500 and 1,000 h. After oxidation, sulfur is detected both in the internal and external zones of the bond coat, at the bond coat/oxide interface and inside the oxide scale. An increase of the sulfur signal with oxidation time is registered at the bond coat/oxide interface for the MCNG-based systems whereas the opposite trend is observed for the AM1-based ones.

6 citations


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BookDOI
01 Jan 2015

128 citations

Journal ArticleDOI
TL;DR: In this paper, a high strength high γ ′ fraction of nickel-based superalloy powder RR 1000 has been hot isotatically pressed (HIPed) at different temperatures.
Abstract: A high strength high γ ′ fraction nickel-based superalloy powder RR 1000 has been hot isotatically pressed (HIPed) at different temperatures. Microstructural analysis and assessment of the tensile properties were performed on these samples. It was found that HIP led to the formation of (Hf,Zr)O 2 particles on prior particle boundaries (PPBs) which were not present in the as-received powder. It is suggested that the oxides are formed by the diffusion of Hf and Zr from the interior of powder particles to the particle surfaces where oxygen level is usually high. When different HIP temperatures were used, no obvious effect on oxide size and distribution was observed but there was an effect on the microstructure and tensile properties. Thus, HIPing at super-solvus temperatures reduced the density of PPBs over the density observed in samples HIPed at sub-solvus temperatures by making grains within the original powder particles grow beyond the precipitates on PPBs, resulting in larger grains with serrated boundaries. Slow cooling from HIPing temperatures also led to the formation of irregular-shaped γ ′. The 0.2% yield strengths at room temperature and at 700 °C were found to decrease with increase of HIP temperature but the high temperature ultimate tensile strengths and elongation increased considerably. Increasing HIPing temperature from sub-solvus to super-solvus temperatures also led to the transition of fracture mode from interparticle debonding to transgranular fracture mode.

98 citations

Journal ArticleDOI
TL;DR: In this article, a nickel-based superalloy powder RR1000 has been hot isostatically pressed (HIPed) and heat treated to produce different microstructures using a scanning electron microscope (SEM).

65 citations

Journal ArticleDOI
TL;DR: Inconel 718 powders have been hot-isostatic-pressed (HIPed) at representative temperatures to investigate the variations in microstructure, tensile properties and tensile fracture mode of the powder compact as discussed by the authors.
Abstract: Inconel 718 powders have been hot-isostatic-pressed (HIPed) at representative temperatures to investigate the variations in microstructure, tensile properties and tensile fracture mode of the powder compact. Microstructure of the powder compacts were characterized by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and so on. The results showed that the interdendritic precipitates inherited from the powders were partially retained in the powder compacts when the powders were HIPed at or below 1210 °C but were eliminated when HIPed at and above 1260 °C. The grain size uniformity of the powder compacts first increases and then decreases with increasing HIPing temperature. Prior particle boundaries (PPBs) were observed in the powder compacts HIPed at and below 1260 °C but was eliminated when HIPed at 1275 °C. The PPBs were decorated with carbide particles, the amount of the carbide particles at the PPBs decreases with increasing HIPing temperature. Most of the PPBs were pinned by the carbide particles in the compacts HIPed at 1140 °C. When the HIPing temperature was increased to 1210 °C and 1260 °C, a large number of PPBs de-pinned and moved beyond the pinning carbide particles, leading to grain growth and leaving carbide particles at the site of the original PPBs within the new grains. With increasing HIPing temperature, the 0.2% yield strength of the powder compacts at 650 °C decreases, the tensile elongation increases, and the tensile fracture mode changed from inter-particle dominant fracture to fully dimple ductile fracture.

62 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of strain distribution in a simple forging geometry on the propensity for recrystallization, and its impact on mechanical properties has been investigated in a newly developed experimental nickel-based superalloy.
Abstract: In the current study, the effect of strain distribution in a simple forging geometry on the propensity for recrystallization, and its impact on mechanical properties has been investigated in a newly developed experimental nickel-based superalloy. The new alloy was produced via a Powder Metallurgy (PM) route and was subsequently Hot Isostatic Processed (HIP), isothermally forged, and heat treated to produce a coarse grain microstructure with average grain size of 23–32 μm. The alloy was examined by means of Electron Back-Scatter Diffraction (EBSD) to characterise the microstructural features such as grain orientation and morphology, grain boundary characteristics and the identification of potential Prior Particle Boundaries (PPBs) throughout each stage of the processing route. Results at the central region of the cross-section plane parallel to the loading direction showed significant microstructural differences across the forging depth. This microstructural variation was found to be highly dependent on the value of local strain imparted during forging such that areas of low effective strain showed partial recrystallisation and a necklace grain structure was observed following heat treatment. Meanwhile, a fully recrystallised microstructure with no PPBs was observed in the areas of high strain values, in the central region of the forging.

52 citations