Characterization Of Oxide Scales Research Articles

On the Early Stage Isothermal Oxidation of APS CoNiCrAlY Coatings

The aim of this study is to analyze the evolution of microstructural and room temperature mechanical properties of air plasma sprayed (APS) CoNiCrAlY coatings before and after early stage high-temperature oxidation. To this purpose, selected samples were isothermally heat treated at 1110 °C for different durations. Phase analysis and oxide scale characterization were performed using x-ray diffraction. Morphological and microstructural features of as-sprayed and oxidized CoNiCrAlY coatings were analyzed by scanning electron microscopy and energy dispersive x-ray spectroscopy. After heat treatment, a duplex oxide scale, composed of an inner α-Al2O3 layer and an outer spinel-type oxide layer, was observed on coating top-surface. The nanoindentation technique was employed to study the evolution of the mechanical properties. An increase in Young’s modulus and hardness with increasing the aging time was observed, this effect was mainly addressed to the partial densification of coating microstructure.

Microstructural characterization of oxide scales formed on steels P91 and P92

In this paper, an in-depth study of steam oxidation of two 9Cr ferritic-martensitic steels (P91 and P92), for advanced power plant, has been carried out. The steels investigated were exposed to a 100% flowing steam environment at 650°C for 1,000 – 3,000 hours. Metallographic analysis showed a multilayered scale was formed on both substrates consisting of an outer Fe-rich phase and inner Fe – Cr spinel, of varying oxide stoichiometry, as well as Cr –Mn-rich bands. The results of scale thickness measurements showed that the oxide formed on the P92 steel was thicker compared to that on the P91 steel. Crystallographic analysis showed that the P91 steel exhibited a martensite to ferrite transformation adjacent to scale – substrate interface which was not observed on the P92 steel. The outer oxide layer on both substrates exhibited a region of equiaxed grains followed by a region of columnar crystal growth. However, on the P91 steel the longer exposure time (3,000 hours) resulted in the outer layer having a region with coarsened equiaxed magnetite grains. The roles of alloying elements (Cr, Mo, W and Mn) were investigated to provide a better understanding of the oxide growth behaviour.

Depth Sensing Indentation of Oxidized Plasma Sprayed CoNiCrAlY Coatings

The aim of the present work is to analyze the evolution of microstructural and mechanical properties of Air Plasma Sprayed (APS) CoNiCrAlY coatings after early stage high-temperature oxidation. Phase analysis and oxide scale characterization were performed by using X-Ray Diffraction (XRD). The microstructural features of CoNiCrAlY coat- ings were analyzed by Scanning Electron Microscopy (SEM), while Nanoindentation (NI) technique was employed to study the evolution of the mechanical properties.

Microstructural characterization of oxide scales formed on steels P91 and P92

In this paper, an in-depth study of steam oxidation of two 9Cr ferritic-martensitic steels (P91 and P92), for advanced power plant, has been carried out. The steels investigated were exposed to a 100% flowing steam environment at 650°C for 1,000 - 3,000 hours. Metallographic analysis showed a multilayered scale was formed on both substrates consisting of an outer Fe-rich phase and inner Fe - Cr spinel, of varying oxide stoichiometry, as well as Cr - Mn-rich bands. The results of scale thickness measurements showed that the oxide formed on the P92 steel was thicker compared to that on the P91 steel. Crystallographic analysis showed that the P91 steel exhibited a martensite to ferrite transformation adjacent to scale - substrate interface which was not observed on the P92 steel. The outer oxide layer on both substrates exhibited a region of equiaxed grains followed by a region of columnar crystal growth. However, on the P91 steel the longer exposure time (3,000 hours) resulted in the outer layer having a region with coarsened equiaxed magnetite grains. The roles of alloying elements (Cr, Mo, W and Mn) were investigated to provide a better understanding of the oxide growth behaviour.

Characterization of oxide scales to evaluate high temperature oxidation behavior of Ti(C,N)-based cermets in static air

Two Ti(C,N)-based cermets with Ni and Ni–20Cr metallic binder were oxidized at 800 °C and 1000 °C for up to 100 h in static air, and the oxide scales and the transition layers formed on both the cermets were characterized to evaluate their high temperature oxidation behavior in static air using XRD, SEM and EDS. The oxide scales formed on both the cermets at 800 °C and 1000 °C were not dense, and were multi-layered, consisting of NiO outerlayer, NiTiO3 interlayer and TiO2-based innerlayer. The transition layers were present between the oxide scales and the substrates with increasing oxidation time, which consisted of Ti-based, Ni-based and Mo-based oxides. Oxidation process of both the cermets was mainly controlled by O inward thermodynamic activity, and oxidation at 1000 °C was faster than that at 800 °C. However, cermet with Ni–20Cr metallic binder was oxidized slower than cermet with Ni metallic binder, due to the richness of Cr in Ni-based binder phase and the rim phase of Ti(C,N) ceramic grains. Cr was completely oxidized to form Cr0.17Mo0.83O2, and was incompletely oxidized to Cr-rich Ti-based oxides, leading to the decrease of O inward thermodynamic activity.

High Temperature Alloys from Nb-Cr-Si System with Minor Additions

Several Nb based alloys (Nb-20Mo-15Si-25Cr, Nb-20Mo-15Si-25Cr-5B, Nb-20Si-20Cr-5Al, and Nb-20Cr-20Si-5Hf) have been prepared to evaluate the oxidation resistance from 700 to 1400°C in air. The phase identification was determined by calculating the isothermal sections in this temperature range using PANDATTM software. The experiments involve static heating for 24 hours (short term oxidation, STO) or 7 cycles of 24 hour heating (long term oxidation, LTO). Weight gain per unit area as a function of either temperature (STO) or time (LTO) has been used to determine their oxidation resistance. However, SEM, EDS on SEM, x-ray mapping, and XRD have been used to evaluate the oxide scale characterization and the influence of various microconstituent effects have been determined. It appears that B addition may be beneficial while Al is advantageous in comparison to Hf addition. The problem of pesting, typically, in a range of temperature from 900 to 1100°C needs to be controlled through minor additions since the alloys exhibit fairly good resistance at lower and higher temperatures up to 1400°C.

Characterization of oxide scales thermally formed on single-crystal silicon carbide

Microstructures of oxide scales thermally formed on single-crystal silicon carbide were investigated using transmission electron microscopy. The oxide scales were formed on the Si-face of 6H-SiC at 1273-1473 K in dry oxygen. Spherical patterns were observed on the surfaces of the oxidized samples by an optical microscope in some regions. In these regions, cross-sectional transmission electron microscopy (TEM) observations show that the oxide scale was divided into two layers; the upper layer (surface side) was composed of crystalline silica, and the lower layer on the silicon carbide substrate was amorphous silica, while the oxide scales in the surroundings of the patterns were composed of only amorphous silica. The oxidation activation energy in the amorphous silica layer of the Si-face of 6H-SiC was found to be 408 kJ/mol by the evolution of thickness directly measured from the cross-sectional scanning electron microscopy and TEM images.

Characterization of Oxide Scale on Alloy 446 by X-Ray Nanobeam Analysis

To understand the potential degradation of metallic interconnects, tubes of alloy 446 were exposed to air/hydrogen dual atmosphere at elevated temperatures for 1030 h. The scale developed on the air side consisted of two layers. Because the two sublayers in the oxide scale were too thin for evaluation by regular X-ray diffraction, nanobeam X-ray diffraction was used to study the phase compositions in the scales that formed on both the air and hydrogen sides of alloy 446. The results indicate that Mn{sub 1-x}Cr{sub 2-x}O{sub 4} spinel is the major phase in the oxide scale on alloy 446. The valence of manganese in the oxide scale was also evaluated by X-ray near-edge absorption.

Microstructural Characterization of Oxide Scale Formed by Early Stage of Oxidation of 17%Cr-Mn-Ni Austenitic Stainless Steel

The microstructure of oxide scale formed in the early stage of oxidation of cold-rolled sheets of 17%Cr-Mn-Ni austenitic stainless steel was examined using SEM and TEM. Samples were oxidized at 973 to1373K for 1 to 15min. Nodules were observed on the surfaces of specimens oxidized at 1173K. The nodules were composed of two layers, which comprised Fe oxides and Cr-rich Fe-Cr-Mn oxides, respectively. The other scale was composed of two layers of Fe-Cr-Mn oxides with different compositions. Nodules were not observed on the surfaces of the specimens oxidized at 973 and 1373K. After oxidation at 1373K for 1min, the scale was composed of three layers. The first layer consisted of Fe-Mn oxides with a spinel structure, the second consisted mainly of Cr oxides, and the third consisted of Cr-Mn oxides containing a small amount of Fe.

Characterization of oxide scales to evaluate high temperature oxidation behavior of Ni–20Cr coated superalloys

Modern thermal spray processes such as plasma spraying are usually considered to deposit high-chromium, nickel–chromium coatings onto the superalloys to enhance their high temperature oxidation resistance. The purpose of these coatings is to form long-lasting oxidation protective scales. In the current investigation, Ni–20Cr alloy powder was deposited on three Ni-base superalloys; Superni 75, Superni 600 and Superni 601 by shrouded plasma spray process. Oxidation kinetics was established for the uncoated as well as the coated superalloys in air at 900 °C under cyclic conditions for 50 cycles by thermogravimetric technique. Each cycle consisted of 1 h heating followed by 20 min of cooling in air. All the coated superalloys nearly followed the parabolic rate law of oxidation. X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive X-ray (SEM/EDAX) techniques were used to characterise the oxide scales. The coating was found to be successful in maintaining its integrity with the superalloy substrates in all the cases. The oxide scales formed on the oxidized coated superalloys were found to be intact and spallation-free in general. The XRD analysis revealed the presence of phase like NiO, Cr 2O 3 and NiCr 2O 4 in the oxide scales. The XRD results were further supported by the SEM/EDAX analyses.

Characterization and properties of oxide scales on hot-rolled strips

The characterization of oxide scale formed on hot-rolled strips is of great importance to subsequent processing such as pickling and cold rolling. The current study indicated that there is a complex relationship of pickling to the scales properties, involving grain size, phases and grain boundary character. By means of electron backscattered diffraction (EBSD), the microstructure and phases were clearly identified. The experimental results show that the oxide scale in large grain size is easily pickled; and FeO is easily resolved in acid than Fe 3O 4. In addition, the scale with high percentage of random grain boundaries is also easily pickled.

Characterization of Oxide Scales Formed on High-Velocity Oxyfuel-Sprayed Ni-Co-Cr-Al-Y + ReTa Coatings

A high-velocity oxyfuel-sprayed 30 wt.% Ni-20 wt.% Co-30 wt.% Cr-10 wt.% Al-2 wt.% Y-4 wt.% Re-4 wt.% Ta coating was oxidized between 1000 and 1200 °C for up to 200 h in air, and the oxide scales were examined. The dense, sprayed coating consisted mainly of Cr3Ni2, Ni3Al, Ni3Ta, Ni, NiO, Al5Y3O12, and Cr2O3. Intermetallics and some oxides formed during spraying. During oxidation, mainly αAl2O3, along with some Al5Y3O12, CoAl2O4, CoCr2O4, Ta2O5, and Ta2O2.2 formed on the coating. The preferential oxidation of Al to form the Al-rich scales resulted in the formation of an Al-depleted region beneath the scales. Rhenium, being the most noble element, was distributed throughout the oxide scale and the coating, without forming any independent oxides.

Characterization of oxide scales formed on low carbon steel between 1100 and 1250 °C in air

A low carbon steel was oxidized isothermally at temperatures of 1100–1250 °C for up to 2 h in air, and the oxide scales were examined. Several hundred micrometer-thick scales formed owing to poor oxidation resistance at high temperatures. Scales consisting mainly of Fe2O3, Fe3O4, and FeO spalled easily, owing to the formation of voids and cracks in the scales. All the alloying elements were also oxidized and incorporated in the iron oxide scales, depending on their local concentration in the matrix.

Oxide scale characterization of hot rolled coils by Raman spectroscopy technique

Abstract The Laser Raman spectroscopy study has shown that different steels have different nature of oxides which leads to the variation in picklability behavior. The present study has shown that Raman spectroscopy is a dependable tool to characterize the oxides.

Characterization of Oxide Scales formed on TiAl-W-Zr Alloys

Characterization of Oxide Scales formed on TiAl-W-Zr Alloys

Characterization of oxide scales formed on HVOF NiCrAlY coatings with various oxygen contents introduced during thermal spraying

NiCrAlY coatings with oxygen contents ranging from 3 to 21 at.% introduced during HVOF spraying were prepared. Oxidation tests at 1000 °C for up to 1000 h showed that the composition and microstructure of the oxide scale formed on the coatings were significantly affected by the oxygen content in the coatings.

Microstructural and microtextural characterization of oxide scale on steel using electron backscatter diffraction.

High-temperature oxidation of steel has been extensively studied. The microstructure of iron oxides is, however, not well understood because of the difficulty in imaging it using conventional methods, such as optical or electron microscopy. A knowledge of the oxide microstructure and texture is critical in understanding how the oxide film behaves during high-temperature deformation of steels and more importantly how it can be removed following processing. Recently, electron back-scatter diffraction (EBSD) has proved to be a powerful technique for distinguishing the different phases in scales. This technique gives valuable information both on the microstructure and on the orientation relationships between the steel and the scale layers. In the current study EBSD has been used to investigate the microstructure and microtexture of iron oxide layers grown on interstitial free steel at different times and temperatures. Heat treatments have been carried out under normal oxidation conditions in order to relate the results to real steel manufacturing in industry. The composition, morphologies, microstructure and microtexture of selected conditions have been studied using EBSD.

Characterization of Oxide Scales Formd on Fe3Al, Fe3Al-Cr, Fe3Al-Cr-Mo, Ni3Al and Ni3Al-Cr Alloys

Alloys of <TEX>$Fe_3$</TEX>Al, <TEX>$Fe_3$</TEX>Al-6Cr, <TEX>$Fe_3$</TEX>Al-4Cr-1Mo, <TEX>$Ni_3$</TEX>Al, and <TEX>$Ni_3$</TEX>Al-2.8Cr were oxidized at <TEX>$1000^{\circ}C$</TEX> in air, and the oxide scales formed were studied using XRD. SEM, EPMA, and TEM. The oxide scales that formed on <TEX>$Fe_3$</TEX>Al-based alloys consisted primarily of <TEX>$\alpha$</TEX>-<TEX>$Al_2$</TEX><TEX>$O_3$</TEX> containing a small amount of dissolved Fe and Cr ions, whereas those that formed on <TEX>$Ni_3$</TEX>Al-based alloys consisted primarily of <TEX>$\alpha$</TEX>-<TEX>$Al_2$</TEX><TEX>$O_3$</TEX>, together with a small amount of <TEX>$NiAl_2$</TEX><TEX>$O_4$</TEX>, NiO and dissolved Cr ions. For the entire alloys tested, nonadherent oxide scales formed, and voids were inevitably existed at the scale-matrix interface.

Characterization of Oxide Scales Formed on Ni3Al-7.8%Cr-1.3%Zr-0.8%Mo-0.025%B

Characterization of Oxide Scales Formed on Ni3Al-7.8%Cr-1.3%Zr-0.8%Mo-0.025%B

Rutherford backscattering spectrometry (RBS) characterization of oxide scale formed on (AISI-304) steel after surface deposition of lanthanum

Oxidized AISI-304 steel samples coated with lanthanum have been investigated by Rutherford backscattering spectrometry (RBS) in order to determine the composition profile of the oxide scale. In this sense, RBS technique has been revealed as a very reliable and nondestructive method for depth profile analysis. Lanthanum deposition, specially over preoxidized specimens, has proven to improve their resistance to high temperature oxidation. The formation of a LaCrO 3 perovskite-like phase uniformly distributed along the oxide scale is proposed as being responsible for this behaviour.