Formation Of Oxide Scale Research Articles

Influence of Si on the oxidation behavior of TM-Si-B2±z coatings (TM = Ti, Cr, Hf, Ta, W)

The concept of Si alloyed transition metal (TM) diborides – well explored for bulk ceramics – is studied for five different physical vapor deposited TM-Si-B2±z (TM = Ti, Cr, Hf, Ta, W) coatings, focusing on the oxidation behavior up to 1200 °C. In their as deposited state, all coatings exhibit single phased AlB2 prototype structures, whereby the addition of Si results in dense, refined morphologies with no additional phases visible in the X-ray diffractograms. With already low amounts of Si, the slope of the mass increase during dynamic oxidation flattens, especially for Ti-Si-B2±z, Cr-Si-B2±z, and Hf-Si-B2±z. Above distinct Si contents, the formation of a steady state region exhibiting no further mass increase is promoted (starting at around 1000 to 1100 °C). Best results are obtained for Hf0.21Si0.18B0.61 and Cr0.26Si0.16B0.58 (both around 2.4 μm thick in the as deposited sate), revealing drastically retarded oxidation kinetics forming 400 nm thin oxide scales after 3 h at 1200 °C in ambient air (significantly lower compared to bulk ceramics). This highly protective oxidation mechanism is attributed to the formation of an amorphous Si rich oxide scale. The Si content needed to form these oxide scales largely differs between the TM-Si-B2±z coatings investigated, also diversifying the prevalent oxidation mechanism, especially for Cr-Si-B2±z.

Influence of oxygen content on structure, thermal stability, oxidation resistance, and corrosion resistance of arc evaporated (Cr, Al)N coatings

(CrxAl1-x)(OyN1-y)ε coatings with different oxygen fractions were prepared by cathodic arc evaporation through variation of injected oxygen flux, and elaborated concerning structure, mechanical properties, thermal stability, oxidation resistance, and electrochemical properties. A moderate addition of O into (Cr, Al)N coatings generates a (Cr, Al)(O, N) solid solution with a face-centered cubic structure, whereas an additional corundum-structured (Cr, Al)2O3 solid solution is formed with superfluous oxygen introduced. The addition of O effectively improves the thermal stability by retarding the formation of w-AlN as well as the dissociation of the CrN bond, allowing the oxynitride coatings to maintain higher hardness after annealing. Notably, a small fraction of O-addition (e.g. 8 or 21 at.% in non-metal sublattice) enhances significantly the resistance against oxidation to above 1100 °C by facilitating the formation of a protective Al-rich oxide scale. Further incorporation of O gives rise to a development of oxide scale with unity elemental distribution and hence results in inferior oxidation resistance. Nevertheless, the O-rich oxynitride coatings provide better protection against electrochemical corrosion while the N-rich coatings exhibit higher corrosion current as well as lower polarization resistance compared to the CrAlN coating.

Evaluation on steel corrosion in water-based drilling fluids: Inhibitors and scale involvement

The purpose of this research is to investigate the behaviour of steel corrosion protection in four different fluids; seawater, tap water, 10 ppg sodium chloride (NaCl) and 12 ppg potassium formate (HCOOK) which are typically used as drilling fluid in oil and gas platform. Corrosion assessment of steel exposed to simulated underbalanced drilling (UBD) wells has been examined via immersion test by weight loss technique. The experiment was carried out in high pressure-high temperature (HPHT) for 30 h in the laboratory stirred autoclave. Two commercial corrosion inhibitors were used in studying the behaviour of the surface protection. Results showed the corrosion rate was dependent on the types of fluids and inhibitors used. The order of corrosion severity or rate of steel corrosion in the individual fluids are; tap water < HCOOK < seawater < NaCl. The observation on the surface morphology through electron microscope depicted the uniform corrosion was the predominantly attack rather pitting and oxide scale formation. The scale formation on the steel surface were discussed.

High-temperature oxidation behaviour of nanostructure surface layered austenitic stainless steel

The present study investigates the high-temperature oxidation behaviour of nanostructure surface layered AISI 304L stainless steel. A severely deformed layer of ∼300 μm thickness, consisting of nanoscale grains (∼40 nm size) in the topmost region, is successfully developed using the surface mechanical attrition treatment (SMAT) process. The SMATed layer is substantially stable up to 700 °C; however, the surface hardness is reduced by ∼37% at 800 °C for 25 h oxidation duration. Glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy analysis revealed the considerable difference in the chemistry and elemental distribution across the oxide scale of SMATed and non-SMATed specimens. Adherent, denser, and thinner scale, dominated by nanocrystals of Cr- and Mn-rich oxides, is formed on the SMATed steel. However, the Fe-oxide dominated scale containing micro-crystals is found on the non-SMATed specimens, which shows noticeable exfoliation. A high density of grain boundaries and lattice defects in the SMATed layer display admirable reactive diffusion properties of Cr and Mn during oxidation of steel, instigating the formation of a protective oxide scale. The SMATed specimens exhibit multiple zones in the oxide scale: (i) Cr/Mn depleted outer layer, (ii) Cr-/Mn-rich inner layer, and (iii) gradually decreasing Cr/Mn region.

Protective TixSiy coatings for enhanced oxidation resistance of the ɣ-TiAl alloy at 900 °C

Due to well-balanced mechanical properties and density ratio, ɣ-TiAl alloys have been extensively investigated for potential aircraft jet engine applications. However, their use is restricted by limited oxidation resistance at temperatures above 750 °C. The present study focuses on the development of titanium silicide protective coatings using different Si reservoirs (3.0 μm, 6.0 μm and 9.5 μm of initial Si thickness) deposited by magnetron sputtering, followed by different periods (2 h to 24 h) of vacuum thermal annealing at 950 °C. The growth of titanium silicides and evolution of the composition and microstructure following oxidation was investigated using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD) techniques. The initial Si thickness and annealing time have an influence on the formation of different zones of composition, assigned as the TixSiy layer, interdiffusion zone and TiAl2 zone, which are correlated with their oxidation behavior at 900 °C in laboratory air after 100 h. The ɣ-TiAl substrates with Si-based coatings presented a protective inner layer of TixSiy. The coatings with initial 3 μm of Si show formation of mixed Si and Ti oxides as well as minor Al content, and traces of Cr at the oxide scale. The oxidation process is described by the parabolic oxidation coefficient, kp, with values of kp = 3.5–8.9 × 10−12 g2·cm−4·s−1 for the coated surfaces, one order of magnitude lower than for the bare substrate. In comparison, the coating systems possessing a higher initial Si thickness (6.0 μm and 9.5 μm) mainly exhibit the mixed formation of dense Si and Al oxide scales with significant Cr enrichment.

Formation of thermal oxide scale and its adhesion to hot-rolled low carbon steels with different final strip thicknesses

Currently, the steelmaking industry produces iron oxide waste scale resulting in pollution to the environment. It was necessary to have a good understanding of the composition, characteristics and properties of the oxide scale. This study focused on the formation of scale and its adhesion to the hot-rolled steel strip with different thicknesses. The oxide scale formed on an as-received hot-rolled steel strip was investigated by X-ray diffraction (XRD), scanning electron microscopy equipped with energy dispersive X-ray (SEM-EDS). Magnetite, hematite and iron were found from the XRD results of all samples, which had the thickness strip of 8, 10 and 12 mm. The scale was thinner for the thinner strip. The adhesion test was conducted by a tensile testing machine adapted with an observation set. The strain initiating the first spallation and mechanical adhesion energy was lowest for the sample with the highest thickness (12 mm). These results indicate that the waste scale produced by hot rolled steel industry can be controlled by the final strip thickness. There was a need to control the scale of waste in a reasonable way to protect the environment.

A Study of the Mechanism of Formation of Composite Oxide Scale on Heat-Resistant Steel 25Cr18Ni9Si2

A Study of the Mechanism of Formation of Composite Oxide Scale on Heat-Resistant Steel 25Cr18Ni9Si2

Oxidation kinetics and microstructure evolution of high Mn stainless-steel alloy in CO2 at 700 °C

Oxidation kinetics and scale formation were examined in 21–2N Stainless Steel alloys in a CO2 environment at 700 °C. Several characterization techniques were used to identify the morphology, crystallographic structure, and chemical composition of the oxide scale formation during exposures up to 1925 h. High manganese content played an important role in homogenous oxide scale formation of Mn3O4 and MnCr2O4 at the scale/gas and scale/alloy interfaces and as an FCC stabilizer in the alloy. Depletion of Mn resulted in an FCC to BCC phase transformation at the scale/alloy interface. No carburization was observed, indicating that the oxide layer is preventing carbon uptake.

Insights on the effect of water content in carburizing gas mixtures on the metal dusting corrosion of iron

Constituents of syngas, such as water, carbon monoxide and sulfides, can cause the degradation of the steel pipes they move through, leading to carbon dusting and corrosion. In spite of considerable attention to this process, many questions remain about its origin. We conduct reactive molecular dynamics simulations of multi-grain iron systems exposed to carburizing gas mixtures to investigate the effect of water content on metal dusting corrosion. To simulate carbon monoxide (CO) dissociation followed by carbon diffusion, we employ an extended-ReaxFF potential that allows accounting for both the high C atoms coordination in bulk iron as well as the lower C coordination at the iron surface and interfaces. The reactions happening in the sample at different water concentrations and at different time frames are explored. We demonstrate that the presence of water on a clean Fe surface promotes different catalytic reactions at the beginning of the simulations that boost the C, H, O diffusion into the sample. At later stage, the formation of oxide scale leads to an elevated concentration of H2O/OH molecules on the surface due to the decrease in Fe affinity to dissociate water. This results into blocking the Fe catalytic sites leading to lower C and O diffusion to the bulk of the sample.

Influence of Water Vapor and Temperature on the Oxide Scale Growth and Alpha-Case Formation in Ti-6Al-4V Alloy

The Ti-6Al-4V alloy is extensively used in aerospace, automotive and biomaterial applications. In the aerospace industry, the service temperature of Ti-6Al-4V is currently limited to 350 °C due to its insufficient oxidation resistance. Oxidation at higher temperatures causes the formation of a fast-growing oxide scale and an oxygen-enriched subsurface layer, which is known as the “alpha-case.” Additionally, the effect of water vapor on the oxidation behavior is critical. In the present study, the oxidation behavior of Ti-6Al-4V in dry air and air containing 10 vol.% H2O at 500, 600 and 700 °C for up to 500 h has been investigated. The main focus of this study is the examination of the different oxide scale morphologies along with the oxygen enrichment in the subsurface zone. It has been observed that spallation of the oxide scale is more severe in a water vapor-containing environment. In dry air, the oxide morphology shows the typical layered TiO2/Al2O3 structure after exposure at 700 °C for 300 h, while Al2O3 precipitates are present in the outermost part of the TiO2 scale when oxidized in wet air. This indicates that the solubility and diffusivity of Al3+ ions in TiO2 are influenced by water vapor. In addition, the extent of oxygen enrichment in the subsurface zone (alpha-case) as a function of temperature and time is determined by nanoindentation profiles. It was shown that in contrast to the scale formation, the alpha-case thickness is not affected by the presence of water vapor in the atmosphere.

Formation of high-temperature inner oxide scale on low alloy steels: Segregation, partitioning and transformation reactions

High-temperature oxide scales on two low-alloy steels were carefully studied. For the first time, the FeO inner scale on the steel with low Cr and Si contents is observed to incur a eutectoid reaction in a divorced mode during cooling, resulting into a bimodal Ni distribution near the scale/substrate interface. In contrast, a combination reaction of oxygen and FeO layer occurs on the steel with high Cr and Si contents where cracks in scales provide pathway for oxygen transport, and a fine-grained nanocomposite oxide band develops near the interface. Dealloying, partition and segregation during the scale formation are comprehensively addressed.

High temperature erosion of T22 steel coated by Cr–Ni electroplating, HVOF sprayed stellite–6 and WC–12Co

In present study, erosion behavior of ASTM–A213–T22 steel (T22 steel) coated by different coating processes was evaluated at high temperature. Cr–Ni electroplating and high–velocity oxy–fuel (HVOF) spraying using Stellite–6 and WC–12Co powders were chose as coating processes. Average coating thicknesses of the Cr–Ni electroplated coating and the HVOF sprayed Stellite–6 and WC–12Co coatings were 40 µm, 226 µm and 200 µm respectively. Oxide scale formation on an uncoated T22 steel specimen and coated specimens was done by covered the specimens with a synthetic coal ash and then annealed under a synthetic flue gas at temperatures of 700 °C with annealing times of 24 h 72 h and 123 h. After oxide scale formation process, the specimens were eroded in erosion tester at temperature of 700 °C using SiC erodent particle with average particle size of 60 µm at impingement velocity of 40 m s−1 and impingement angles of 30° and 90°. The experimental results showed that erosion rate of the specimens dramatically increased with increasing of exposure time at 700 °C. Erodent impingement angle was unaffected to erosion rate of the uncoated T22 steel, the Cr–Ni electroplated and the HVOF sprayed Stellite–6 and WC–12Co coatings. Microcracks, debonding of coating as well as deep cavities were observed on eroded surface of the uncoated T22 steel, the Cr–Ni electroplated and the HVOF sprayed Stellite–6 and WC–12Co coatings. Erosion resistance of the HVOF sprayed Stellite–6 coating was highest compared with that of the Cr–Ni electroplated and the HVOF sprayed WC–12Co coating. The superior erosion resistance of the HVOF sprayed Stellite–6 coating was due to high hardness, more thickness and low porosity of the deposited coating.

High-temperature wear and cyclic oxidation behavior of (Ti, W)C reinforced stainless steel coating deposited by PTA on a plain carbon steel

(Ti, W)C reinforced stainless steel coatings were fabricated by plasma cladding for investigating the role of (Ti, W)C particles on microstructure, cyclic oxidation and high-temperature wear resistance of the coatings. (Ti, W)C particles were uniformly dispersed in the coatings and exhibited a diffusion-metallurgical bond with the (Fe, Ni) matrix. Although adding (Ti, W)C to the coating reduced the oxidation resistance due to the low thermal stability of these carbides , the rapid formation and thickening of oxide scale could alleviate the sticking problem in actual rolling condition. Moreover, (Ti, W)C addition resulted in the rapid formation and excellent maintenance of the tribo-oxide glaze during the sliding process, which remarkably improved the wear resistance and reduced the coefficient of friction . • (Ti, W)C particles were uniformly dispersed in the coatings and exhibited ametallurgical bond with the (Fe, Ni) matrix. • Adding (Ti, W)C to the coating reduced the oxidation resistance due to low thermal stability of the (Ti, W)C particles. • The rapid formation and thickening of oxide scale caused by (Ti, W)C addition could alleviate the sticking problem. • The rapid formation and excellent maintenance of the glaze was performed on the worn surface by (Ti, W)C addition. • (Ti, W)C addition significantly improved the high-temperature wear resistance and reduced the coefficient of friction.

Proving the Availability of Ni–Fe Anode for Electro-Reduction of Solid V2O3 in Molten Fluoride Salts

The availability of casting Ni–Fe alloy as inert anode for direct electro-reduction of V2O3 in molten Na3AlF6-K3AlF6-AlF3 was investigated. The electrochemical oxidation behavior of anode as well as microstructural evolutions of formed oxide scale were systematically studied. The electrochemical characterization and reaction mechanism of the cathode oxide were also investigated to evaluate the influence of alloy anode on cathodic reduction process. The in situ formed three-layered oxide scale is compact and coherent, which is composed of an outermost Fe2O3 + FeAl2O4 skin layer, a Fe2O3 middle layer and a FeAl2O4 inner layer. The skin layer has a continuous, smooth structure and shows electrochemical activity. The Fe2O3 layer with a compact structure prevents inward diffusion of electrolyte and outward migration of metal cations. The innermost FeAl2O4 layer shows a loose structure and functions as a buffer layer to improve the peeling resistance of oxide scale. With the continuous extension of polarization time, the inner FeAl2O4 layer is slowly oxidized and becomes thinner, simultaneously, the dense Fe2O3 layer becomes thicker. Ultimately, metal vanadium product with fine rod-like particles can be obtained and the oxygen content in the metal vanadium is below 0.3 mass% within electrolyzing time of 2 h. The corresponding current efficiency is around 63%.

Improved oxidation and hot corrosion resistance of the NiSiAlY alloy at 750 ℃

The oxidation and hot corrosion behaviors of the NiAlY alloy, NiCrAlY alloy and NiSiAlY alloys with different Si content (1, 3 and 5 wt%) were investigated at 750 ℃. With the addition of Si, the oxidation resistance of the NiSiAlY alloys was significantly improved compared to the undoped NiAlY alloy. The doped Si promoted the formation of the protective oxide scales. Moreover, the NiSiAlY alloys exhibited enhanced resistance to the NaCl-induced hot corrosion in both dry and humid environments. Si played a beneficial role in restraining the internal corrosion and consumption of Al. In addition, the oxidation and hot corrosion mechanisms of the tested alloys were also discussed.

Hot corrosion behaviour of CNT-reinforced ZrO2-Y2O3 composite coatings on boiler tube steel at 900°C

PurposeIn Indian thermal power plants, the main cause of boiler tube failure is the presence of molten sulphates and vanadates, which deteriorate the tube material at high temperatures. To combat the hot corrosion failure of metals, thermal spray technology is adopted. This study aims to investigate and study the effect of hot corrosion behaviour of carbon nanotube (CNT)-reinforced ZrO2-Y2O3 composite coatings on T-91 boiler tube steel in a molten salt environment at 900 °C for 50 cycles.Design/methodology/approachA plasma spray technique was used for development of the coatings. The samples were exposed to hot corrosion in a silicon tube furnace at 900 °C for 50 cycles. After testing, the test coupons were analysed by X-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and cross-sectional analysis techniques to aid understanding the kinetics of the corrosion reaction.FindingsCNT-based reinforced coatings showed lower weight gain along with the formation of protective oxide scales during the experimentation. Improvement in protection against hot corrosion was observed with increase in CNT content in the coating matrix.Originality/valueIt is pertinent to mention here that the high temperature behaviour of CNT-reinforced ZrO2-Y2O3 composite on T-91 steel at 900°C temperature in molten salt environment has never been studied. Thus, the present research was conducted to provide useful results for the application of CNT-reinforced composite coatings at elevated temperature.

The evaluation of oxide scale formation during hot corrosion of Rene-80 superalloy under thermal shock at different dwell times

ABSTRACT In this study, the oxide scale formation on the Rene-80 superalloy after hot corrosion under thermal shock has been investigated. The X-ray diffraction (XRD) and field-emission scanning electron microscope (FE-SEM) were used for the phase identification and evaluation of oxide scale, respectively. The hot corrosion test under thermal shock was performed by depositing Na2SO4 salt at the beginning of each cycle on the surface of the specimens. The results showed that hot corrosion occurred intermittently with the basic fluxing mechanism of the oxide scale and re-precipitation of discontinuous and porous oxides. The growth rate of the Cr2O3 layer increased with decreasing the dwell time per cycle and the dissolution of titanium. Decreasing the dwell time in each hot corrosion cycle increased the growth rate of the Cr2O3 layer, the chromium depletion from the substrate/oxide scale interface, the internal oxidation of aluminium, and the internal sulfidation of chromium.

Corrosion Phenomena of High Temperature Alloys by Helium Impurities in the Primary Coolant of HTGR

The primary coolant circuit of the high temperature gas-cooled reactor (HTGR) contains trace impurities. A nickel base alloy would corrode when exposed to an atmosphere at a high temperature and for a long time. The protective oxide scale formed by chromium is an important factor to prevent severe corrosion of high temperature alloys. Corrosion tests were conducted on Inconel 617, Incoloy 800H, Hastelloy X, and T-22, which are commonly used in the steam generator of HTGR. The alloys were exposed to helium with trace impurities for 48 hours at 950°C. The corrosion results were analyzed by weighing, scanning electron microscopy (SEM) and electron probe microanalyzer (EPMA). All the four alloys formed oxide scales in this atmosphere, but they differ in the capacity to resist corrosion. Therefore, the carbon transfer phenomenon observed in this experiment varies for the different alloys. In addition, for Cr in Inconel617, the expected depletion phenomenon near the corrosion layer occurred, which is consistent with the results from theoretical analysis.

Oxide Scale Formation of EN 1.4622 and EN 1.4828 Stainless Steels during Annealing and Descaling Behavior in Neutral Electrolytic Pickling

Oxide scale formation during short‐term annealing and electrolytic pickling behavior of ferritic EN 1.4622 and austenitic EN 1.4828 stainless steels are investigated. The annealing is performed at temperatures between 1000 and 1100 °C for ferritic and 1100 and 1200 °C for austenitic steel grade under humid atmospheres in simulated industrial process. Neutral electrolytic pickling, also referred to as neutral electrochemical pickling or the Ruthner Neolyte Process, is performed in Na2SO4 electrolyte, and pickling efficiency is evaluated visually and by image analysis of pickled surfaces. The results show that annealing conditions have a more impactful effect on the structure and the composition of the resulting oxide in the austenitic grade within the studied condition range. The thicknesses of the ferritic scales are mainly less than 0.4 μm, while almost all austenitic scales are thicker than it. In addition, the amount of silicon oxide formation inside the steel matrix of the austenitic and ferritic grades is highly different. Longer exposure times and higher temperatures promote scale growth during annealing, resulting in inefficient electrolytic pickling for the ferritic grade. For the austenitic grade, almost all steel surfaces are still covered with oxide scale after electrolytic pickling.

A Review on the Wear, Corrosion and High-Temperature Resistant Properties of Wire Arc-Sprayed Fe-Based Coatings.

Among different thermal spraying methods, arc-spraying has been widely used due to its low operating costs and high deposition efficiency. The rapid progress of cored wire technology in arc-spraying has increased possibilities for the preparation of new Fe-based coating materials with enhanced properties by adding reinforcement particles and alloying elements to suit the different applications. Fe-based coatings have been extensively used because of their high strength, toughness, lower production costs, and availability of raw materials. This makes them suitable replacements for Ni-based coatings in ambient and high-temperature applications. This review discusses the research status and developments of the arc-sprayed Fe-based coatings. The study specifically reviews the wear behavior, corrosion analysis, and high-temperature resistant properties of arc-sprayed Fe-based coatings, aiming to develop an understanding of the protection mechanisms for Fe-based coatings. The performance of the Fe-based coatings depends on the integrity of the coating structure. Optimizing arc-spraying parameters minimizes defects (pores, grain boundaries, unmelted particles, oxides, and microcracks) that deteriorate the coating properties. High amorphous phase content, ceramic reinforcement particles and alloying elements enhance the corrosion, tribological, and high-temperature resistant properties of Fe-based coatings. In high-temperature applications, Fe-based coatings form oxide scales that protect the coating from further oxidation; thus, it is important to select the optimum composition for the alloying elements.