Effect Of Pre-oxidation Treatment Research Articles

Improvement of the durability of thermal barrier coating by pre-oxidation

To suppress thermally grown oxides (TGO) in thermal barrier coatings (TBCs), the effect of pre-oxidation treatment was investigated for different thermal spray processes, such as high-velocity oxy-fuel spraying (HVOF) and low-pressure plasma spray (LPPS). A pre-oxidation treatment was applied before or after the top coat processing. When the pre-oxidation treatment was applied before top coat processing, TGO growth was suppressed during isothermal oxidation compared to when pre-oxidation was applied after the top coat process. Thermal spray processing did not affect the TGO growth behavior.

Microstructure and oxidation response of Mo-Si-B-ZrB2 alloy at 900 °C: Effect of pre-oxidation treatment

Microstructure and oxidation response of Mo-Si-B-ZrB2 alloy at 900 °C: Effect of pre-oxidation treatment

Effect of Pre-Oxidation Treatment on Corrosion Resistance of FeCoSiBPC Amorphous Alloy

In this paper, the corrosion resistance of FeCoSiBPC amorphous alloy after pre-oxidation and non-oxidation heat treatment is investigated. The corrosion behaviors of Fe80Co3Si3B10P1C3 amorphous alloys in 1 mol/L NaCl solution were investigated by the electrochemical workstation. The pre-oxidation heat treatment can improve the corrosion resistance of FeCoSiBPC amorphous alloy through an increase in the Ecorr value from −0.736 to −0.668 V, which makes it easy to reach a passive state. The corroded morphology and products of amorphous alloys were tested by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM/TEM analysis showed that, after pre-oxidation treatment, the oxide layer was divided into two layers: the inner layer was amorphous, the outer layer appeared crystalline, and the main oxide was Fe2O3. During the oxidation process, Co and P elements diffused from the inner layer to the outer layer, forming phosphorus and cobalt oxides with high corrosion resistance on the surface of the ribbon, thereby improving the corrosion resistance of the ribbon.

Effect of pre-oxidation treatment on the hot corrosion behavior of pack-cemented aluminide coatings on the K438 alloy in salt mixture

The hot corrosion test was carried out for the pack-cemented aluminide coatings on the K438 Ni-based alloy containing 50 wt.% NaCl + 50 wt.% Na2SO4 salt mixture at 1050 ℃ in air. This study aimed to add the salt mixture only once to the surface of the as-received and pre-oxidation aluminide coatings to investigate the influence on the subsequent and long-term hot corrosion behavior of coatings. The specimens were studied using a combination of gravimetry and several surface-analytical techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), focused ion beam (FIB), and transmission electron microscopy (TEM). The oxide scale on the surface of the pre-oxidation aluminide coating was denser and maintained better integrity after hot corrosion. The rod-like precipitate phase of CrS was mainly formed in the substrate of the two coatings. The sulfur was concentrated around Cr2O3 and corrosion cavities were observed in the oxide scale on the surface of the as-received aluminide coatings. Furthermore, a schematic mechanism of the hot corrosion process of the aluminide coatings was proposed, emphasizing the effect of pre-oxidation.

Effect of preoxidation treatment with H2O2 on ruthenium ion-catalyzed oxidation of Yima long flame coal

Environmental concerns have led researches to investigate carbon neutral and sustainable strategies to satisfy well-being of present and future generations, in which coal oxidation becomes a promising approach to achieve this goal. In this study, Yima long flame coal (YLFC) was subjected to ruthenium-ion-catalyzed oxidation (RICO) after peroxidation with H2O2 (PO). The results indicate that the organic matter in YLFC is mainly oxidized into benzenecarboxylic acids, accounting for 70.36% of all the oxidation products, and the yields of the valuable resulting carboxylic acids are significantly elevated by PO from 12.99 wt% to 35.06 wt%, leading to a higher utilization of carbon and lower CO2 emission. Moreover, PO can enhance remarkably the reactivity of the macromolecular precursors of coals, especially highly condensed aromatic species to produce benzenepentacarboxylic acid and mellitic acid more efficiently with a 20-fold increase and 200-fold increase, which is ascribed to the formation of carboxyl groups from other oxygen-containing groups or bonds in coals via PO. The reactive intermediates OH and OOH generated from H2O2 decomposition can attack the carbon atom of alkyl side chains, ether bonds, C=O bonds, and the bridged linkages to undergo a preliminary degradation of macromolecular networks in coals and produce more active sites for the subsequent RICO, leading to the yield and species number increase of carboxylic acids via PO.

High temperature oxidation behavior of Ni-based superalloy Nimonic95 and the effect of pre-oxidation treatment

The high-temperature oxidation behaviors of Nimonic95 alloy at 800 °C, 900 °C and 1000 °C were studied. The diffusion process of alloying elements in different stages of oxidation was studied and analyzed, and the pre-oxidation process was established. The results showed that multilayer oxide films formed in the air at 800 °C, 900 °C and 1000 °C, the outer layer was mainly Cr2O3 with a small amount of Al2O3, TiO2 and composite oxides such as CrTi spinel. The inner layer was mainly Al2O3. Nimonic95 alloy has excellent oxidation resistance at 800 °C and 900 °C, but poor oxidation resistance at 1000 °C and the oxide film peeled off in a short time. The oxidation resistance of Nimonic95 alloy at 1000 °C can be improved significantly by pre-oxidation at 800 °C for 140 h.

High temperature corrosion of Hastelloy C22 in molten alkali salts: The effect of pre-oxidation treatment

The optimum protective oxide layer was expected to provide protection and reduce the corrosion damage of superheater material. The corrosion behaviour of raw and pre-oxidised Hastelloy C22 was investigated by exposing the selected samples to molten alkali salts (95.5 wt% KCl +4.5 wt% NaCl) at 700 °C for 100 h. The pre-oxidised Hastelloy C22 exhibited better corrosion resistance than raw Hastelloy C22 during exposure to molten alkali salt. The pre-oxidation treatment delayed the penetration of the corrosive reagent into the superalloy substrate. Schematic models of oxidation behaviour and corrosion mechanism in molten salts were presented in this work.

The tribological properties of bulk Fe2B with pre-oxidation treatment at 750°C in air

Purpose The purpose of this study was to investigate the tribological properties of bulk Fe2B with pre-oxidation treatment.Design/methodology/approach Bulk Fe2B was oxidized in an electric box furnace with a soaking time of 9 min under 750°C in air. Then, the tribological experiments were carried out on an UMT-Tribolab tester.Findings The oxide layer was composed of Fe, Fe2O3, Fe3O4, B2O3 and H3BO3. The oxidative direction of bulk Fe2B was perpendicular to the sample surface. But, the oxidative direction of Fe2B crystals was irregular. At 0.1 m/s, the friction coefficient was the lowest. The effects of shortening the running-in period of friction and reducing the friction coefficient by pre-oxidation treatment at 0.1 m/s were remarkable. Nevertheless, the effect of pre-oxidation treatment was futile at 0.2 m/s. Wear mechanisms of oxidized Fe2B mainly were adhesive and abrasive wear.Originality/value The effects of shortening the running-in period of friction and reducing the friction coefficient by pre-oxidation treatment were remarkable.

Influence of alloyed Fe on corrosion of Ni-Cr alloys in molten silicates and the effects of pre-oxidation treatment

The corrosion of Ni-Cr-xFe alloys (x = 6, 16, 25 wt.%) with a pre-oxidation treatment was studied in molten silicates at 1000 °C and 1050 °C. The microstructure of oxide scales following pre-oxidation treatment changes with an increase in Fe content. This content affects the mode of failure of the oxide scales at the beginning of corrosion. A failure mechanism of oxide scales is proposed, based on the microstructure evolution during corrosion. In addition, the temperature increase from 1000 °C to 1050 °C leads to an accelerated dissolution of the oxide scales without affecting the corrosion mode itself.

The Effect of Pre-oxidation Treatment on Corrosion Behavior of Ni–Cu–Fe–Al Anode in Molten CaCl2 Salt

This article presents Ni–Cu–Fe–Al alloy as a novel inert anode used in FFC process (the Fray Farthing Chen) in molten calcium chloride salts for producing titanium. The alloy was prepared by vacuum induction melting; then utilized as anode material in molten CaCl2 for 16 h at 900 °C. Morphology and the corrosion behavior of the samples were analyzed using scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The product on the cathode was analyzed using X-ray diffraction (XRD). After 16 h electrolysis of anodes, EDS and SEM analysis of the samples showed that the corrosion depth of the non-oxidized sample was shorter. Corrosion attacks more severe for the pre-oxidized sample than the non-oxidized sample, which indicated that the corrosion resistance of outer layer is higher on the non-oxidized sample. The XRD results show that the TiO2 pellets were successfully reduced to the lower oxides using the Ni–Cu–Fe–Al inert anode.

Improvement of oxidation resistance of 9 mass% chromium steel for advanced-ultra supercritical power plant boilers by pre-oxidation treatment

Effect of pre-oxidation treatment on oxidation resistance in steam at 650°C has been investigated for 9 mass% chromium (Cr) steel for advanced ultra-supercritical power plants. The formation of thin scale of Cr2O3-rich oxides is achieved by pre-oxidation in argon gas containing 0.3ppm oxygen, which significantly improves the oxidation resistance of the steel in steam at 650°C for a long time exceeding 20,000h. Effects of pre-oxidation conditions, such as oxygen concentration in argon gas and pre-oxidation temperature and time, and of silicon concentration in the steel on the oxidation resistance in stream are systematically investigated.

Electrochemical Corrosion of HVOF-Sprayed NiCoCrAlY Coatings in CO2-Saturated Brine

The effect of pre-oxidation treatment and surface preparation of optimized NiCoCrAlY coatings deposited by high-velocity oxygen fuel (HVOF) spraying and exposed to a low-temperature corrosive environment is reported herein. Coatings with two surface finish conditions (as-sprayed and ground) were heat treated under two different oxygen partial pressures (air and argon). The electrochemical corrosion behavior was evaluated in CO2-saturated brine via potentiodynamic polarization, polarization resistance, and electrochemical impedance measurements. The results show that the grinding process and pre-oxidation treatment in argon enhanced growth and formation of α-Al2O3 scale. The potentiodynamic polarization results show that both pre-oxidation and surface treatment had a positive influence on the corrosion resistance of the coating. The reduction of the porosity and the formation of a dense, uniform, and adherent oxide scale through pre-oxidation treatment led to an increase of the corrosion resistance due to a decrease in active sites and blocking of diffusion of reactive species into the coating. However, according to the results, complete transformation from metastable alumina phases to α-Al2O3 in addition to formation and growth of dense α-Al2O3 is required to ensure full protection of the coating and base material over long periods.

The effect of pre-oxidation treatment on the corrosion behavior of amorphous Al1−xZrx solid-solution alloys

The electrochemical behavior of as-deposited and pre-oxidized amorphous Al1−xZrx solid-solution alloys (x=0.25, 0.32, 0.49, 0.65, 0.74) in 1M HCl was investigated by the micro-electrochemical technique. It was found that, for higher Zr alloying contents, x≥0.49, the as-deposited Al1−xZrx alloys exhibit passive corrosion behavior due to the formation of a protective Zr-rich passive film on the Zr-rich alloy surface. The native oxide layer on the as-deposited Al-rich Al1−xZrx alloys (x<0.49) is much less stable, which rapidly results in a total break-down of the protective character of the native Al-rich oxide layer upon anodization in 1M HCl. The pre-oxidized am-Al1−xZrx alloys all exhibited superior corrosion behavior as compared to their as-deposited pendants, attaining passive current densities as low as 3.5×10−2μA/cm2 at 1000mV. The superior corrosion resistance of the pre-oxidized alloys is attributed to a combination of characteristics of the thermally-grown amorphous (Al0.33Zr0.67)O1.83 overlayer: (i) a relatively high Zr fraction, (ii) a structurally and chemically uniform microstructure, (iii) a stable, minimal residual growth defect structure (in the surface region) established by a sufficiently large time of oxidation.

A Study on Graphitization of 4H-SiC(0001) Surface under Low Pressure Oxygen Atmosphere and Effects of Pre-Oxidation Treatment

Effects of residual oxygen in an annealing chamber on graphitization of SiC along with surface pre-treatment process have been investigated. As a pre-treatment process, SiO2 was formed on 4H-SiC(0001) substrates by thermal oxidation before graphene formation annealing. Epitaxial graphenes were formed in several O2 pressures and effects on graphitization of SiC were evaluated. It is shown that quality of graphene on SiC substrates which formed without pre-oxidation degraded by the presence of residual O2 in the chamber. It is demonstrated that SiO2 pre-oxidation films (about 10nm) were effective to prevent such degradations, for all O2 pressures that we examined in this work. In addition, at O2 pressure of 1.1x10-1Pa, with SiO2 pre-oxidation, a graphene growth rate was increased, which indicates that a certain level of O2 pressure enhances graphene growth.

Effect of pre-oxidation treatment on the bonding strength and thermal shock resistance of SiC coating for C/C–ZrC–SiC composites

To improve the bonding strength and thermal shock resistance of SiC coating for C/C–ZrC–SiC composites, a transition layer with mechanical interlocking structure was constructed at the interface by pre-oxidation treatment and chemical vapor deposition. For the coated specimens with pre-oxidation treatment at 1073K for 5min, the bonding strength increased from 2.0 to 4.0N, and the mass loss percentage decreased by 52.5% after 12-time thermal cycling between 1773K and room temperature in air. The transition interlocking structure can effectively alleviate the mismatch between the coefficients of thermal expansion of SiC coating and C/C–ZrC–SiC substrate, improving the bonding strength and thermal shock resistance. As the pre-oxidation time increases, a rugged and loose ZrO2–SiO2 layer will be formed at the interface, which is disadvantageous to the bonding strength and thermal shock resistance of SiC coating for C/C–ZrC–SiC composites, and results in the debonding and collapse of the coating.

Effect of pre-oxidation on the oxidation resistance of spinel-coated Fe–Cr ferritic alloy for solid oxide fuel cell applications

Low-temperature-sintered MnCo2O4–MnO2 coatings have been prepared on pre-oxidized SUS430 ferritic alloy by slurry coating. The effect of pre-oxidation treatment before slurry coating is then investigated. Microstructural and electrical characterizations show that 25 h of pre-oxidation at 800 °C could significantly improve the oxidation resistance of the coated alloy and effectively inhibit the increase in area-specific electrical resistance during long-term oxidation. These effects can be explained by the interfacial reactions between the coating and the pre-oxidized alloy during sintering and oxidation tests. Furthermore, this study suggests that the dense reaction layer at the coating-alloy interface could be the key to improving the oxidation resistance of metallic interconnects with low-temperature-sintered spinel coatings.

The effect of pre-oxidation treatment on the plasticity behavior of B2 iron aluminide

The paper presents the structure and morphology of scale layers formed as a result of isothermal oxidation in the air of a FeAlCrZrB alloy in the temperature range 700–1100 °C, during 200 h. The scale consisted of three aluminium oxide forms (γ, θ and α), existing together as a mixture or separately, depending on the oxidation temperature. The compression tests showed that an improvement in the plasticity of a B2 FeAl-based alloy at room temperature can be achieved by forming aluminium oxide layers on the specimen surface.

The Effect of Pre-Oxidation Treatment on the High-Temperature Oxidation of Co–Re–Cr Model Alloys at Laboratory Air

The aim of a pre-oxidation treatment at low oxygen partial pressure is to promote the formation of a Cr2O3 (or Al2O3) scale in such a way that the oxide layer can reliably prevent the contact of oxygen with the metallic substrate also at high oxygen partial pressure. In this study, the pre-oxidation treatment was applied to the two alloys Co–17Re–23Cr and Co–17Re–30Cr (at.%). Pre-oxidation of the Co–Re–xCr alloys was found to be non-protective for the metallic substrate at high oxygen partial pressure despite the formation of a Cr2O3 layer. Different kinds of Cr2O3 scale damage were observed depending on the Cr concentration. The Cr2O3 scale formed on the alloy Co–17Re–23Cr loses its protective properties as a result of cation transport by lattice and grain boundary diffusion, while the Cr2O3 scale formed on the alloy Co–17Re–30Cr degraded as a consequence of scale cracking. In addition, the effect of alloying with Si was investigated and found to be promising.

Effect of Pre-Oxidation Treatment on the Thermal Shock Resistance of Thermal Barrier Coatings in a Combustion Gas Environment

Thermal barrier coatings (TBCs) were deposited by an Air Plasma Spraying (APS) technique. The TBC coating comprised of 92 wt.% ZrO2 and 8 wt.% Y2O3 (YSZ), CoNiCrAlY bond coat, and MarM247 nickel base super alloy. After APS of YSZ two batches of TBC specimens were tested, one batch of which was pre-oxidised in air for 10h at 1080 oC. Both types of the specimens were directly pushed into a combustion gas at 1150 oC for 25 min and then out to the natural air for quenching. The combustion gas was produced by burning jet fuel with high speed air in a high temperature wind tunnel, which simulates the real service conditions in an aeroengine. Results show that TBCs prepared by the APS had good thermal shock resistance in the combustion gas. The pre-oxidation treatment of the TBC had a significant effect on its thermal shock life. The as-oxidised TBCs always had worse thermal shock resistance than the as-sprayed ones after thermal shock cycles.

Effect of pre-oxidation treatment on the corrosion behaviour of Ni–Ti alloys in eutectic (Li, K)2CO3 mixture at 650°C

The effect of pre-oxidation treatment at 650°C in air on the corrosion behaviour of binary Ni–Ti alloys containing 5, 10, and 15 wt-%Ti in eutectic (Li, K)2CO3 at 650°C in air has been investigated. The results indicate that the pre-oxidation of the alloys can produce an almost pure TiO2 scale. Nevertheless, this TiO2 scale cannot hinder the formation of NiO outside and beneath the TiO2 scale during subsequent molten salt corrosion. The corrosion rates of the alloys decrease with increasing content of titanium in the alloys. The corrosion of the alloys proceeds mainly by inward diffusion of oxygen through the TiO2 layer, forming large quantities of NiO beneath the TiO2 layer. Compared with Ni–5Ti and Ni–10Ti, the formation of NiO on Ni–15Ti is inhibited significantly, especially in the initial stages.