Oxidation behavior of thermal barrier coatings with HVOF and detonation-sprayed NiCrAlY bondcoats

Well-adhered gamma-Al2O3 coating layers can be formed on FeCrAl metallic supports for the preparation of structured catalysts in diesel particulate filter (DPF) systems using a three-step method-pre-oxidation, primer deposition and coating deposition. The optimal pre-oxidation is at 950 degreesC for 10 h; the optimal primer sol calcination is at 800 degreesC for 3 h; and the optimal gamma-Al2O3 slurry calcination is at 900 degreesC for 2 h. If the oxidation temperature is 1050 degreesC, only 0.5 h is required to obtain almost the same coating adhesion level as at 950 degreesC for 10 h. The data concerning effects of the major preparation parameters (the pre-oxidation time, temperature, primer calcination temperature and the coating calcination temperature) are presented herein. The coating adhesion was measured by ultrasonic adhesion, thermal shock and interface shear strength tests. (C) 2002 Elsevier Science B.V. All rights reserved.

A method to form well-adhered γ-Al2O3 layers on FeCrAl metallic supports

https://hal.archives-ouvertes.fr/hal-01989245/document

High temperature oxidation of IN 718 manufactured by laser beam melting and electron beam melting: Effect of surface topography

Effect of thermo-mechanical processing on oxidation of austenitic stainless steel 316L in supercritical water

An experimental study of the coking tendency of nine different materials was carried out in a quartz electrobalance setup with a jet stirred reactor (JSR) under industrially relevant ethane steam cracking conditions: Tmaterial = 1159 K, Ptot = 0.1 MPa, χethane = 73%, dilution δ = 0.33 kgH2O/kgHC. A strong influence of the composition of the materials on the coking rate as a function of time on-stream was observed. The initial coking rate varied from 5 × 10–4 g·m–2·s–1 to 27 × 10–4 g·m–2·s–1, while the asymptotic coking rate changed in the range of 2 × 10–4 g·m–2·s–1 to 6 × 10–4 g·m–2·s–1. SEM and EDX analyses of coked and uncoked coupons revealed that the composition of the oxide layer in contact with the cracked gas, formed after the initial preoxidation or decoking, has an important influence on the amount of coke deposited. Materials that formed a thin Al2O3 layer on the coupon surface showed a higher coking resistance. A uniform surface composition and a high resistance to spalling and fractures are o...

Influence of the Reactor Material Composition on Coke Formation during Ethane Steam Cracking

The effect of surface roughness on the properties of the oxide scale formed on Fe–Cr–Al alloys during oxidation in air at high temperatures has been investigated. Large and systematic differences in scale thickness, in the composition of the oxides forming the scale, and in the residual stess levels are found.

Effect of Surface Roughness on Oxidation: Changes in Scale Thickness, Composition, and Residual Stress

Residual stress near edges and corners of thermally grown alumina scaleswere investigated. In this study, an edge is the intersection of twoorthogonal flat surfaces and a corner is the intersection of three suchsurfaces. Microfluorescence measurements, performed on alloys withcomposition Fe–28Al–5Cr (at.%, bal. Fe) oxidized at 900°C,showed a large (>50%) reduction in hydrostatic stress in the vicinity ofedges and corners. Surprisingly, significant stress reduction persists outto distances twenty to fifty times the scale thickness from theedge. Finite-element analysis calculations confirm the experimental resultsand provide a considerably more detailed picture of the stress distributionand its components and show that much of the observed stress reduction nearan edge, is due to plastic deformation of the underlying metal.

Effect of Edges and Corners on Stresses in Thermally Grown Alumina Scales

Using grazing-emission X-ray fluorescence (GEXRF), isothermal oxidation of the alloys 55Fe–25Cr–20Ni and 55Fe–25Cr–20Ni(+0.3Y) (wt.%) were studied as a function of oxidation time at 750 °C in O2. In addition, the effect of thermal cycling was studied. Using GEXRF, oxide thickness, the Cr-depletion zone in the substrate, and Fe and Ni concentrations in the oxide were monitored as a function of oxidation time. Scanning-electron microscopy was used to independently measure the Cr-depletion zone. Raman spectroscopy was used to measure the concentration of Fe2O3 appearing in the oxides in early oxidation (less than 2 h). Both GEXRF and Raman measurements show that the thermally-grown chromium oxide purifies with extended oxidation; initially abundant Fe2O3 became undetectable after 2 h of oxidation. However, the total Fe concentration was still ∼3% after 2 h but systematically decreased with further oxidation. Thermal cycling had no effect on these results.

Chromium-oxide Growth on Fe–Cr–Ni Alloy Studied with Grazing-emission X-ray Fluorescence

Nondestructive optical techniques have been used to study the oxidation of low-index crystal faces of single-crystal β-NiAl as a function of temperature. Using these techniques, residual stress, phase composition, and thickness of the scales were determined at various temperatures. The oxidation of the three low-index surfaces, (001), (110), and (111) exhibit discernible differences. Consistently lower stress values are observed on (001) surfaces. Fluorescence and Raman results indicate a higher concentration of θ-Al2O3 on (001) faces and lower concentrations on (111) faces at all temperatures between 800 and 1200°C. Although the residual stresses are higher on (110) faces, these are the only surfaces which maintain adherence up to 1450°C. All surfaces exhibit a stress anomaly between 1200 and 1250°C.

Optical Investigation of the Effects of Substrate Orientation on Oxidation of Single Crystal β-NiAl

The oxidation of 55Fe–25Cr–20Ni (wt.%) alloys, with and without added reactive element (RE) Y, were studied using grazing-emission X-ray fluorescence (GEXRF). Samples were studied after isothermal treatments at 750°C in O2 and after cyclic-oxidation treatments. In early-stage oxidation, a Ni-rich scale is formed. The distribution of this early-stage Ni deposit is studied as the scale evolves. The Ni deposit, serving as a marker, remains on the outer scale surface in Y-containing alloys, but is not detectable in scales on Y-free alloys. The results indicate that new chromia scale growth occurs at the outer surface in Y-free alloys but, for Y-containing alloys, new growth occurs away from the outer surface. Thus, a shift in the growth mode is apparently observed at 750°C, consistent with higher-temperature observations. However, unlike the high-temperature measurements, scale-growth rates are not significantly affected by the RE.

S. Uran

Papers

Effect of Surface Roughness on Oxidation: Changes in Scale Thickness, Composition, and Residual Stress

Effect of Edges and Corners on Stresses in Thermally Grown Alumina Scales

Chromium-oxide Growth on Fe–Cr–Ni Alloy Studied with Grazing-emission X-ray Fluorescence

Optical Investigation of the Effects of Substrate Orientation on Oxidation of Single Crystal β-NiAl

Influence of a reactive element on the growth of a thermally grown chromia scale: A grazing emission X-ray fluorescence study