Thin Oxide Scale Research Articles

Oxidation-dominated wear behaviors of carbide-based cermets: A comparison between WC-WB-Co and Cr3C2-NiCr coatings

A WC-40WB-12Co coating has been developed and demonstrated to have comparable oxidation resistance, remarkably enhanced hardness (over 2 times higher) and improved wear resistance (2–4 times higher) than the widely used Cr3C2-25NiCr coating at elevated temperatures. Wear failure of Cr3C2-NiCr coating was dominated by severe subsurface cracking due to oxidation and its poor high-temperature mechanical properties. By contrast, in the WC-WB-Co coating, the thin oxide scale formed on the surface increased lubrication and hindered further oxidation. The WC-WB-Co coating provided strong mechanical support for the oxide layer. The coating thereby achieved an outstanding high-temperature wear performance. Based on detailed comparisons, the wear mechanisms of these carbide-based cermet coatings at elevated temperatures were proposed.

Study of titanium alloy Ti6242S oxidation behaviour in air at 560°C: Effect of oxygen dissolution on lattice parameters

High temperature oxidation of titanium alloy Ti6242S was studied in air at 560 °C up to 10000 h. Oxidation kinetics obeys a parabolic law (kp = 8.7 × 10−15 g². cm−4.s-1). Oxygen dissolution in the metal was found to represent between 80 and 90% of the total mass gain. Thin oxide scales are mainly composed of TiO2, in top of which some alumina is present. Titanium nitride was detected as a very thin layer at the outer part of the metallic substrate. Underneath, the oxygen dissolution area was found to reach the maximum brittleness after 1000 h of oxidation.

Electrophoretic co-deposition of Fe2O3 and Mn1,5Co1,5O4: Processing and oxidation performance of Fe-doped Mn-Co coatings for solid oxide cell interconnects

Fe-doped Mn1,5Co1,5O4 coatings on Crofer22APU were processed by an electrophoretic co-deposition method and the corrosion resistance was tested at 750 °C up to 2000 h.The “in-situ” Fe-doping of the manganese cobalt spinel was achieved by electrophoretic co-deposition of Mn1,5Co1,5O4 and Fe2O3 powders followed by a two-step reactive sintering treatment. The effects on the coating properties of two different Fe-doping levels (5 and 10 wt.% respectively) and two different temperatures of the reducing treatment (900 and 1000 °C) are discussed. Samples with Fe-doped coatings demonstrated a lower parabolic oxidation rate and thinner oxide scale in comparison with both the undoped Mn1,5Co1,5O4 spinel coating and bare Crofer 22 APU. The best corrosion protection was achieved with the combined effect of Fe-doping and a higher temperature of the reducing step at 1000 °C.

Characteristics and high temperature oxidation behavior of Ni-Cr-Y2O3 nanocomposite coating prepared by cathode plasma electrolytic deposition

Ni-Cr-Y2O3 nanocomposite coating, with Y2O3 nano-particles finely dispersed, was prepared by cathode plasma electrolytic deposition from environmental-friendly nickel-trivalent chromium sulfate electrolyte directly. The coating is dense and uniform with typically molten morphology, possessing a nanocrystalline structure with an average grain size of about 30–50 nm. Owing to the synergy effect of the fine-grained structure of the coating and the reactive-element effect of the addition of Y2O3 nano-particles, a thin, compact, uniform and continuous Cr2O3 oxide scale can be formed during 200 h oxidation at 750 °C. Such Cr2O3 oxide scale provides effective protection to the inner alloy and substrate.

Internal Oxidation Prediction by Cellular Automata Approach in Energy Materials at High Temperatures

Aim of the study is the adaptation of a modeling concept to internal oxidation during steam oxidation using the cellular automata (CA) approach. The CA system is implemented for the alloys that undergo most severe corrosion degradation. In this work, steam oxidation process for two solid‐solution strengthened alloys; Haynes® 230®, 617 alloy, two γ’‐strengthened alloys; 263 and Haynes® 282®, and three austenitic steels rich in Cr: 309S, 310S, and HR3C, are analyzed. The study shows that the exposure in steam environment leads to a thin oxide scale formation consisting mainly Cr2O3 and MnCr2O4 spinel type oxide, except alloy 617, where NiCr2O4 spinel is observed. The modeling studies of internal oxidation development are applied to γ’‐strengthened alloys, Haynes® 282® and alloy 263, and are shown to be in good agreement with the experimentally observed pronounced internal oxidation attack.

Steam Oxidation of Austenitic Heat-Resistant Steels TP347H and TP347HFG at 650⁻800 °C.

Steam oxidation of austenitic heat-resistant steels TP347H and TP347HFG at 650–800 °C was investigated. Comprehensive micro-characterization technologies containing Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), X-ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS) were employed to observe and analyze the oxidation products. Results show that breakaway oxidation behaviors were observed on TP347H at 700 °C and 800 °C. The oxidation kinetics of TP347HFG at 650–800 °C followed a parabolic law. The oxide scales formed on TP347HFG were composed of MnCr2O4 and Cr2O3. A thin and protective Cr-rich oxide scale was replaced by Fe2O3 nodules due to the insufficient outward migration of metallic ions, including Cr and Mn at the subsurface of coarse-grain TP347H. Smaller grain of TP347HFG promoted the formation of the compact Cr-rich oxide scales. At higher temperatures, the incubation period for breakaway oxidation of the Cr-rich oxide scale was much shorter because of quick evaporation of the Cr2O3 oxide scale and the slower outward diffusion of metallic ions via the grain boundaries.

Removal of thin oxide scale by ultrasonic cleaning with diluted hydrochloric acid in hot stamping of bare 22MnB5 sheet using resistance heating

A descaling process using ultrasonic cleaning with a diluted hydrochloric acid solution was developed to remove the thin oxide layer formed from the hot stamping of a bare 22MnB5 sheet using resistance heating. The oxide film removal performance and subsequent weldability and paintability were investigated. Since the oxide layer formed by resistance heating is thin, the oxide layer was successfully removed by ultrasonic cleaning with the acidic solution. The occurrence of spattering during resistance spot welding was suppressed, and sufficient weld strength was obtained.

Porosity Developments within 9Cr-1Mo Steel Exposed to CO<sub>2</sub>

When 9Cr-1Mo steel is exposed to CO2-rich advance gas-cooled reactor (AGR) gases it forms a duplex oxide which consists of an outer Fe rich layer and an inner Cr rich spinel which provides oxidation resistance allowing the steel to resist the corrosive atmosphere of the plant. The oxide scale develops, growing both into the substrate and outwards from the initial metal/air interface. The spinel develops porosity through the coalescence of Fe vacancies which over time alters the properties of the oxide and potentially allows a transport network to form within the oxide. The porosity of the duplex oxide was measured using scanning electron microscopy of oxides on 9Cr steel samples oxidised in a CO2 atmosphere. Results show that samples which have suffered breakaway oxidation show larger oxide scales with alternating Fe/Cr bands whereas samples which have yet to suffer from breakaway show higher peak porosity values but thinner oxide scales. Furthermore the samples which are currently under protective oxidation show a high max porosity peak in comparison to those which have suffered breakaway.

The Influence of Thermal Oxidation Parameters on Structural, Friction, and Wear Characteristics of Oxide Layers Produced on the Surface of Ti–6Al–7Nb Alloy

The effects of thermal oxidation of a biomedical titanium alloy (Ti–6Al–7Nb) on its morphology, structure, mechanical properties, and sliding friction and wear against alumina were investigated. It was found that at 600 °C, the surface of the alloy was characterized with a thin inhomogeneous oxide scale. Increasing the temperature of oxidation to 700 °C and 800 °C allowed obtaining homogeneous layers, which fully covered the examined surfaces. By contrast, the oxide scale obtained at 800 °C was composed of big oxide particles with a developed surface. Thermal oxidation process allows a fourfold increase in the hardness of Ti–6Al–7Nb alloy. It was shown that the oxide scale on the examined alloy efficiently enhances its resistance to sliding wear against alumina.

Blanking immediately after heating and ultrasonic cleaning for compact hot-stamping systems using rapid resistance heating

To produce ultra-high-strength steel parts for improving fuel consumption and collision safety of automobiles, a compact hot-stamping process having resistance heating was developed. In this process, a blanking operation was introduced immediately after heating to deal with non-rectangular blanks in resistance heating. By blanking, not only were the blank shapes optimised for stamping but the formability was also improved by removing both non-heating edges in contact with the electrode. A rectangular quenchable steel sheet was resistance-heated; the sheet was immediately blanked into the desired shape, and the blank was hot-stamped. In addition, reinforcements used for a body-in-white were hot-stamped using the proposed process to examine the applicability. The reduction in thickness of the hot-stamped reinforcement using a hot-blanked sheet was reduced compared with that using a rectangular blank. The formability was improved by blanking immediately after heating. Moreover, ultrasonic cleaning with diluted hydrochloric acid removed the thin oxide scale caused by resistance heating, and the spot-resistance weldability and electrodeposition paintability were improved. Blanking immediately after heating and ultrasonic cleaning are useful for practical hot-stamping processes using resistance heating.

Effect of water vapor on the oxidation behavior of HVAF‐sprayed NiCr and NiCrAlY coatings

Isothermal oxidation behavior of NiCr and NiCrAlY coatings deposited onto low alloy 16Mo3 steel by high‐velocity air fuel (HVAF) process was investigated in 5% O2 + 20% H2O + N2 at 600 °C for 168 h. Whereas NiCrAlY showed lower mass gain compared to NiCr, both coatings succeeded in maintaining the integrity with the substrate during the exposure without any breakaway oxidation. A thin Cr‐rich oxide scale (Cr2O3) formed on NiCr, and a thin mixed oxide scale (Al2O3 with NiCr2O4) formed on NiCrAlY significantly increasing the oxidation protection in the presence of water vapor.

Effect of V-addition on the thermal stability and oxidation resistance of CrAlN coatings

Since the superiority of tribological properties, V-containing coatings, with the potential to generate lubricious Magnéli oxides at elevated temperatures, are regarded as excellent candidates for machining applications. Here, a study was conducted to shed light on the intrinsic thermal stability, mechanical properties and oxidation resistance of V-alloyed CrAlN coatings deposited by cathode arc evaporation. The hardness of Cr0.48Al0.52N and Cr0.44Al0.50V0.06N coatings with a single-phase face-centered cubic structure is 30.8 ± 0.9 and 33.0 ± 1.3GPa, respectively. Upon annealing in Ar atmosphere, Cr0.44Al0.50V0.06N coating reveals a retarded precipitation of wurtzite AlN as well as a postponement in Cr–N disintegration as compared to V-free Cr0.48Al0.52N coating, owing to the solid solution of V with a stronger binding capacity with nitrogen. The improved structural stability of Cr0.44Al0.50V0.06N coating contributes to the mild decline in hardness and elastic modulus upon annealing. When exposed to air, the incorporation of V into CrAlN promotes the formation of (Al, Cr)2O3 mixed oxide as well as additional V2O5, leading to a significantly lower onset temperature for oxidation. The existence of V2O5 degrades the protective of (Al, Cr)2O3 oxide layer and causes a complete oxidation of Cr0.44Al0.50V0.06N coating at 950°C, where only a dense and thin oxide scale can be detected in Cr0.48Al0.52N coating.

Oxidation behavior of ferritic stainless steels in simulated automotive exhaust gas containing 5 vol.% water vapor

In this study, the effect of alloying elements, cerium (Ce) and tungsten (W), on the oxidation behavior of medium chromium ferritic stainless steel in simulated automotive exhaust gases containing 5 vol.% H2O was studied in the temperature range of 950–1100 °C for 5 h. The oxidation kinetics and oxide film characteristics were analyzed by means of thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM) and elemental probe micro-analyzer (EPMA). The growth rate of oxidation and oxidation mass gain were significantly decreased on the addition of Ce. A dense, uniform, and thin oxide scale formed on Ce-containing steels. The steel containing Ce and ∼0.5 wt% W displayed similar oxidation behavior compared to the steel containing only Ce. A large number of cracks and pores existed in the oxide film and oxide/metal interface leading to the spallation of oxide film, when the addition of W reached ∼1.0 wt%.

Steam Oxidation Resistance of Advanced Steels and Ni-Based Alloys at 700\xa0\xb0C for 1000\xa0h

The aim of the work was to investigate corrosion resistance of highly alloyed steels and Ni-based alloys in a steam atmosphere for 1000 h at 700 °C. In these steam oxidation experiments, two solid solution strengthened alloys; Haynes® 230®, 617 alloy, two gamma-prime (γ′) strengthened alloys; 263 and Haynes® 282® and three Cr+Ni- rich stainless steels: 309S, 310S and HR3C austenitic steels were exposed. The study showed that the materials exposed commonly developed thin oxide scales; in Ni-based alloys, these consisted of mainly MnCr2O4 spinels and Cr2O3, with the exception of 617 alloy where NiCr2O4 spinels and Cr2O3 were found. In Fe-based alloys, Cr2O3, MnCr2O4 spinels, Fe,Mn(SiO)4, and finally Fe3O4 developed. No evaporation of chromia has been found within 1000 h test period. Furthermore, the development of TiO2 was not observed into a large extent in Haynes® 282® and 263 alloy, in contrast to the study performed at 800 °C under the same steam environment conditions.

Effect of Pressure on Metal Dusting Initiation on Alloy 800H and Alloy 600 in CO-rich Syngas

The effect of pressure on metal dusting initiation was studied by exposing conventional alloys 600 and 800H in CO-rich syngas atmosphere (H2, CO, CO2, CH4, H2O) at ambient and 18 bar total system pressure and 620 °C for 250 h. It was verified that, at constant temperature, increasing the total system pressure increases both oxygen partial pressure (pO2) and carbon activity (a C), simultaneously. Both samples exposed at ambient pressure showed very thin oxide scale formation and no sign of metal dusting. By contrast, samples exposed in the high-pressure experiment showed severe mass loss by metal dusting attack. Iron- and chromium-rich oxides and carbides were found as corrosion products. The distinct pressure-dependent behavior was discussed by considering both thermodynamic and kinetic aspects with respect to the protective oxide formation and pit initiation.

Oxidation performance of repaired aluminide coatings on austenitic steel substrates

The repairability of slurry aluminide coatings on austenitic stainless steels (ASS) and their oxidation behaviour were investigated in this work. Slurry aluminide coatings were deposited on IN-800HT and HR3C substrates to obtain a B2-(Fe,Ni)Al phase. Chemical stripping of the coatings was thereafter conducted with diluted nitric acid. Dissolution occured at the interface between the diffusion and interdiffusion layers of the coating due to the penetration of the nitric solution through the tensile cracks of the coatings. The greater the NiAl content in such interface the greater the dissolution. This was proved by thermodynamic calculations and experimentally with model NiAl and FeAl. Realuminization of the stripped samples resulted in somewhat thicker coatings with similar microstructures as the fresh ones. The oxidation behaviour of the fresh and the repaired coatings was compared under isothermal conditions (650°C and 700°C for, respectively, the IN-800HT and HR3C alloys) in air for 2000h. The loss of Cr from the surface of the coatings and the delayed transformation of the aluminas suggest that there was some chromium evaporation. However, the oxidation behaviour was similar on the new and the repaired coatings. The oxidation kinetics appeared to follow a parabolic law for the HR3C samples. The coatings grew very thin Al2O3 oxide scales at the coating/gas interface but some spallation occurred in IN-800HT. It thus appears that the slurry aluminide coatings can be repaired and supply protection to ASS in air at 650 and 700°C.

Influence of oxidation temperature on the oxide scale formation of NiCoCrAl coatings

Intermetalic coatings of NiCoCrAl have been successfully developed on low carbon steel substrate to improve oxidation resistance in extreme environments. The influence of oxidation temperature on the oxide scale formation was studied in the temperature range of 600-1000 °C. The measurements were made in air under isothermal oxidation test for 100 h. The surface morphology showed that a cauliflower like structure developed entire the oxide scale of sample oxidized at 800 °C and 1000 °C, while partly distributed on the surface of sample oxidized at 600 °C. The XRD analysis identified Cr2O3 phase predominantly formed on the oxidized sample at 600 °C and meta-stable Al2O3 with several polymorphs crystalline structures: η, δ, θ, κ, and α-Al2O3 at relatively high temperatures, i.e. 800 °C and 1000 °C. A Cross-sectional microstructure showed that complex and porous structures formed on the top surface of 600 °C and 1000 °C samples. In contrast, a very thin oxide scale formed on 800 °C oxidized samples and it appeared to act as a diffusion barrier of oxygen to diffuse inward, hence could increase in the service life of carbon steel substrate.

High Temperature Oxidation Behavior of Mg-6%Al-1%Zn-1%CaO Alloys

The magnesium-base AZ61 alloy was cast while adding 1% CaO powder into the melt. It was hot extruded, and oxidized at 550-650℃ in air in order to study its microstructure and oxidation behavior. Initially added CaO powder reacted with Al in the melt to Al₂Ca particles that aligned along the extrusion direction. The formed Al₂Ca particles increased the oxidation resistance through forming the superficial CaO scale at the upper part of the thin MgO oxide scale.

Behavior of Slurry Aluminized Austenitic Stainless Steels under Steam at 650 and 700 °C

Slurry aluminide coatings were deposited on IN-800HT and HR3C austenitic stainless steels. The additive layers were based on B2-(Fe,Ni)Al and contained tensile cracks in a greater extent in HR3C than in IN-800HT. The oxidation kinetics of the aluminized and uncoated steels were then evaluated under 1 bar of steam at 650 and 700 °C till 2000 h. The overall mass gain of the Al-coated IN-800HT was about half that of the uncoated substrate at 650 °C. The oxidation kinetics of the Al-coated IN-800HT were parabolic, but a sub-parabolic regime was found in the uncoated counterparts. In the former, α-Al2O3 grew while the latter developed a very thin scale that could not be accurately characterized. The Al-coated HR3C accumulated a greater specific mass gain than the uncoated steel at 700 °C. However, it is believed that the presence of cracks and of a rougher surface of the coating is responsible for the greater mass gains. Indeed, both the Al-coated and the uncoated HR3C substrates followed sub-parabolic oxidation rate indicative of a very thin oxide scale. The scales were composed of α-Al2O3 in the Al-coated material, while Fe3O4, Fe2O3 and Cr2O3 were found in the uncoated HR3C. No evidence of Cr loss by evaporation of CrO2(OH)2 or of hydrogen permeation was found under the experimental conditions studied here. The aluminide coatings appeared though stable from a metallurgical point of view after the 2000 h of exposure to steam.

High-Temperature Oxidation Behavior of Refractory High-Entropy Alloys: Effect of Alloy Composition

The high-temperature oxidation behavior of a new family of refractory high-entropy alloys (HEAs) with compositions of W–Mo–Cr–Ti–Al, Nb–Mo–Cr–Ti–Al and Ta–Mo–Cr–Ti–Al was studied at 1000 and 1100 °C. Based on these equimolar starting compositions, the main incentive of this study was to select the most promising alloy system whose properties may then be successively improved. Despite the high amount of refractory elements, Ta–Mo–Cr–Ti–Al showed good oxidation resistance at 1000 and 1100 °C. Moderate values of mass gain and complex oxidation kinetics were observed for the W- and Nb-containing HEAs. These alloys formed inhomogeneous oxide scales possessing regions with thick and porous layers as well as areas revealing quite thin oxide scales due to the formation of discontinuous Cr- and Al-rich scales. The most promising behavior was shown by the alloy Ta–Mo–Cr–Ti–Al which followed the parabolic rate law for oxide growth due to the formation of a thin and compact Al-rich layer.