Oxide Scale Adherence Research Articles

Effect of Ta on selective oxidation behavior and oxide film adhesion of alumina-forming austenitic alloys

The effects of Ta on the selective oxidation behavior and scale adhesion of Fe-45Ni-25Cr-4Al-1.5Nb-0.4C-xTa (x=0.6, 0.9, 1.2, 1.5 wt%) austenitic alloys at high temperature under low oxygen pressure were investigated. The FCC, MC-(Ta, Nb)C, M23C6 and B2-NiAl phases were found in the annealed alloy. Addition of Ta significantly promoted the formation of an external Al2O3 layer and inhibited growth of Cr2O3 and spinel at 850 °C under oxygen pressures of 10−18 atm and 10−24 atm. Similar oxidation behavior was observed in two-step oxidation process (650 °C for 8 hours and 1000 °C for 16 hours). Ta and Nb preferentially segregated at the interface between the oxide scale-matrix as well as grain boundary within the oxide scale during oxidation, and inhibited outward diffusion of Al and Cr. A large oxygen activity gradient was formed in the oxide film, resulting in the formation of columnar grains. Due to a significant decrease in oxygen activity at the front of the reaction, selective oxidation of alumina was promoted. Furthermore, the scratch test technique was used to quantify the adhesion of oxide scales. Peg-like structures formed by Ta and Nb positively influenced the adhesion properties of the oxide scale.

Effect of Y on Oxidation Behavior of Directionally Solidified Ni-Based Single-Crystal Superalloy

The effect of yttrium (Y) addition on the oxidation behavior of a Ni-based directionally solidified single-crystal superalloy is investigated in this study. Isothermal oxidation tests for samples with different levels of Y addition are conducted at 1100 °C in air. The Y content of the samples is determined by the actual pickup amount obtained from an Inductively Coupled Plasma-Atomic Emission Spectrometry test. It is discovered that the addition of Y increases the oxide resistance by the scale of an adhesive double-layer oxide, which is composed of Al2O3 and spinel Ni(Cr,Al)2O4. With 70 ppm of Y addition, the oxidation mass gain decreases from 12.6 g/m2 for the alloy without Y addition to 5.3 g/m2, and the oxidation rate decreases significantly. In addition, the internal nitride disappears after Y doping because of an increase in oxidation scale adherence and a decrease in oxidation products. In this study, the alloy with 660 ppm Y addition demonstrates the best oxidation resistance.

Effect of Heat Treatment Temperature on Isothermal Oxidation of Ni-based Fe-33Ni-19Cr Alloy

This project studies the influence of different grain sizes of Ni-based Fe-33Ni-19Cr alloy obtained from heat treatment procedure on high temperature isothermal oxidation. Heat treatment procedure was carried out at two different temperatures, namely 1000℃ and 1200℃ for 3 hours of soaking time, followed by quenching in the water. These samples are denoted as T1000 and T1200. The heat-treated Ni-based Fe-33Ni-19Cr alloy was subjected to an isothermal oxidation test at 950℃ for 150 hours exposure. Oxidized heat-treated alloys were tested in terms of oxidation kinetics, phase analysis and surface morphology of oxidized samples. Oxidation kinetics were determine based on weight change per surface area as a function of exposure time. Phase analysis was determined using the x-ray diffraction (XRD) technique and surface morphology of oxidized samples was characterized using a scanning electron microscope (SEM). As a result, the heat treatment procedure shows varying grain sizes. The higher the heat treatment temperature, shows an increase in grain size with a decrease in hardness value. The oxidation kinetics for both heat-treated samples showed an increment pattern of weight change and followed a parabolic rate law. The oxidized T1000 sample recorded the lowest parabolic rate constant of 3.12×10–8 mg2cm–4s–1, indicating a low oxidation rate, thus having good oxidation resistance. Phase analysis from the XRD technique recorded several oxide phases consisting of Cr2O3, MnCr2O4, and (Ti0.97Cr0.03)O2 oxide phases. In addition, a uniform oxide layer is formed on the oxidized T1000 sample, indicating good oxide scale adhesion, thereby improving the protective oxide behavior.

Nanocrystalline Y2O3-modified metal matrix composite coatings with improved resistance to thermocyclic oxidation and V2O5-induced type II hot corrosion

Incorporating reactive elements (RE) into turbine coatings is a well-established surface treatment. However, suboptimal RE concentrations can lead to compromised strength, heightened brittleness, and reduced adhesion. In contrast, RE oxides offer advantages of avoiding these detrimental effects, counteracting corrosion phenomena induced by V2O5 compounds and enhancing oxidation resistance. A notable challenge lies in optimizing RE oxide particle incorporation and understanding the influence of particles in coating microstructures. This study focuses on developing NiAl and Ni-Cr-Al type metal matrix composite (MMC) coatings on Inconel 617 (IN617), containing up to 11 vol% of Yttria (Y2O3) nanoparticles. Y2O3 nanoparticles and Ni were co-electrodeposited on IN617 followed by either pack aluminizing or a two-step chromizing and aluminizing process. An even distribution of Y2O3 nanoparticles was observed throughout the entire 100 μm coating thickness, leading to significant grain refinement in the sub-micron to nano range in both coating types. Y2O3-strengthened coatings were subjected to oxidation at 1100 °C and hot corrosion at 700 °C and were compared to their Y2O3-free counterparts. Present at grain boundaries, Y2O3 markedly enhanced the oxidation and corrosion resistance by reducing interdiffusion, improving the oxide scale adherence and binding V2O5, highlighting the potential of this method for advanced turbine blade coatings.

The Influence of Mo Content and Annealing on the Oxidation Behavior of Arc‐Melted Cr–xMo–8Si Alloys

The influence of Mo (10–40 at%) additions to Cr–8 at%Si is systematically studied by analyzing arc‐melted alloys in the as‐cast and annealed state. The oxidation resistance is tested by thermogravimetric analysis (TGA) at 1200 °C in air for up to 100 h. Samples are characterized by X‐ray diffraction, scanning electron microscopy, and wavelength‐dispersive X‐ray spectroscopy. The studied Cr–xMo–8Si alloy series shows a beneficial effect of Mo on the corrosion behavior. For all of the investigated Mo contents, no nitridation is observed and the oxide scale adhesion is improved. An increased amount of intermetallic A15 phase leads to the formation of a SiO2 scale beneath the Cr2O3 layer during high‐temperature exposure. The internal SiO2 layer inhibits further internal oxidation of the A15 phase. Uniform size and distribution of A15, benefits the formation of a duplex oxide scale. Cr–25Mo–8 at%Si, shows the most promising oxidation behavior. The TGA data follows the paralinear law, with both the growth rate, kp, and volatilization rate, kv, of Cr2O3 being reduced by adding 10–25 at% Mo. A binary Cr/Mo–Si phase diagram is generated in order to determine accurate annealing conditions and estimate the stability range of the metastable σ phase.

Oxide Scale Formation on Low-Carbon Steels in Future Reheating Conditions

The mitigation of CO2 emissions is one of the major areas of research in iron ore-based steelmaking. In this study, four simulated current and potential future reheating scenarios with different fuel and oxidizer gases were studied regarding the amount of oxide formation and the adhesion of the steel–oxide interface: (1) methane–air; (2) coke oven gas–air; (3) hydrogen–air; (4) and an oxyfuel scenario with 50:50 methane/hydrogen as fuel gases. Isothermal oxidation tests were conducted at temperatures of 1150, 1230 and 1300 °C. Four low-carbon steel grades were tested in the previously mentioned gas atmospheres. The structure and composition of the formed oxide scales was analyzed with FESEM-EDS microscopy. The amount of oxide formation correlated with the water vapor content of the gas atmosphere for all four steel grades; however, notable differences were found between individual steel grades regarding the degree of oxidation increase. No clear evidence was found of the gas atmospheres affecting the adhesion of oxide scales to the steel substrate. The adhesion of the interface was mainly determined by the content of silicon in the steel grade and the test temperature.

(Invited) Pt-Modified Aluminide Coatings for Ni-Base Single Crystal Superalloy

Single phase (Ni,Pt)Al coating has been widely employed as state-of-the-art bondcoat for protecting hot-sectional components in commercial aero engines, especially for the parts made of Ni-base single crystal (SX) superalloys. For high temperature protective coating serving on SX superalloy, two interfaces are vitally essential for acquiring reliably long service life: the interface growing thermally-grown oxide (TGO) and the interface connecting coating and substrate alloy. Normally, the excellent performance of PtAl coating derives from high Al content and the incorporation of Pt, which ensures formation of exclusively adherent oxide scale, α-Al2O3. To further improve the performance of Pt-modified aluminide coating, in present study reactive elements are introduced using co-electroplating method. Compared with singular doping, co-doping of Hf-Y demonstrated superior oxidation resistance. The oxide scale growth rate and spallation tendency of Hf-Y co-doped (Ni,Pt)Al coating were much smaller, as well as the surface rumpling extent. Besides, the grain size of Hf-Y co-doped (Ni,Pt)Al coating was finer than that of Hf- or Y- doped coatings in as-received state, indicating the capability of grain refinement. With the benefits of RE co-doping, the desirably thin/smooth TGO is thus accessible for Pt-modified aluminide coatings. The other issue is the element interdiffusion at high temperature, which would affect the mechanical property of SX superalloy. According to Fick′s law of diffusion, J Al = - D Al · δμ Al / δ x ,to reduce diffusion coefficient ( D Al ) or chemical potential ( δμ Al / δ x ) would both decrease the diffusion extent ( J Al ). Therefore, two strategies are employed: adding a diffusion barrier between coating and substrate, or designing a γʹ-PtAl coating. The performance of these modified aluminide coatings are evaluated in high temperature oxidation test. At last, doping behavior of some elements were explained by First-Principle Calculations.

Differences in Oxidation Behavior of Conventionally Cast and Additively Manufactured Co-Base Alloy MAR-M-509

AbstractHigh-temperature oxidation behavior of conventionally cast and additively manufactured (AM) Co-base alloy MAR-M-509 was compared in the present study. The specimens were exposed in air at 1000 °C and characterized by means of scanning electron microscopy equipped with energy/wavelength dispersive x-ray spectroscopy (EDX/WDX) and electron backscatter diffraction as well as transmission electron microscopy. Substantial differences in the oxidation processes of two alloy versions were observed. Faster oxidation of the cast alloy was mainly induced by (1) oxidation of coarse primary carbides, (2) internal oxidation and nitridation processes and (3) incorporation of other alloy constituents (e.g., Co, Ni, W) into the Cr-oxide scale. AM specimens, in contrast, formed a more homogeneous, thinner and better adherent external oxide scale. The results are discussed in terms of differences in the chemical composition and alloy microstructure, including the grain size distribution in the material and the morphology of the strengthening precipitate phases.

Effect of Y-doping on the microstructural evolution and oxidation resistance of NiAlHf coatings at 1200 °C

The microstructure and oxidation resistance of NiAlHf and NiAlHfY coatings were systematically investigated at 1200 °C in air. The results revealed that Hf-rich oxides, Y-rich oxides, (Hf, Y)-rich oxides distributed at grain boundaries of oxide scale for NiAlHfY coating, which improved the adhesion and spallation resistance of oxide scale. And oxidation weight gains of NiAlHf, NiAlHfY coatings were 2.2425 and 1.8231 mg cm−2, respectively, which was reduced by 18.7% after Y-doping. The enhanced oxidation resistance was attributed to better synergistic effect of Hf and Y impeding ions diffusion. Finally, the Y-doping mechanism responsible for enhanced oxidation resistance was discussed.

Adhesion of thermal oxide scale formed on silicon-containing hot-rolled steel oxidised in oxygen

Defects can be caused by the thermal oxide scale that forms on the surface of steel during the hot rolling process. The oxidation and adhesion of scale on silicon-containing hot-rolled steel were investigated in a flowing 20% O2-N2 gas mixture at 900°C. Scale spallation was observed using a tensile testing machine equipped with a CCD camera. The thickness of the scale was 3.45 μm for the higher silicon steel and 4.86 μm for the lower silicon steel. The oxide scale consists of hematite, magnetite, wustite, and iron. The strain that caused the first spallation was used to calculate the mechanical adhesion energy, which indicated the behaviour of the scale adhesion on a steel substrate. The strain initiation of the first spallation of scale on higher silicon steel was 5.57% which was higher than 4.57% for lower silicon hot-rolled steel. The calculated adhesion energy on the studied steel was shown to be in the range of 281 J.m-2 to 334 J.m-2. It can be noted that the higher amounts of silicon content in hot-rolled steel increased steel-scale interface adherence. This was due to the precipitated silicon oxide near steel-scale interface might be exhibited as a reinforcing phase.

Investigation of oxide scale adhesion on hot-rolled steel using the tensile test and acoustic emission

This article addresses applying a tensile test with a CCD camera to assess scale adhesion on hot-rolled steel as a function of hot-rolled coil position. The scale adhesion in this study was shown in the value of the strain initiating the first scale spallation. The result of strain initiating the first scale spallation was confirmed with an acoustic emission (AE) method. The as-received hot-rolled coil was studied at the head, middle, and tail positions. A scanning electron microscope (SEM) and X-ray diffraction (XRD) were used to examine the scale morphology and phase identification respectively. The results show that the oxide scale comprises hematite and magnetite layers. It was found that the higher strain initiating the first scale spallation was revealed on the scale formed on the hot-rolled coil at the head and middle positions. This indicates that the oxide scale was more difficult to remove than at the tail position of the coil. The scale growth and cooling affects the stresses on the oxide layer and the steel substrate. A thin oxide layer on tail position of the hot-rolled coil will easily first crack and then buckle and followed by spallation, while a thick scale on head and middle positions of the hot-rolled coil was harder than that thin scale.

Enhancing oxide scale growth and adhesion via electrochemically regulating ion diffusion

Pre-oxidation is a common surface treatment approach to enhance the corrosion resistance of metals, which suffers from slow ion diffusion kinetics, bad oxide scale adhesion, and weak compactness. Herein, we propose an electrochemical oxidation approach in molten carbonate to improve the oxide scale growth and adhesion via electrochemically regulating ion diffusion in the formed oxide scale. An anodic polarization applied at the metal substrate enlarges the chemical potential gradient of oxygen and offers a favorable electric field across the metal/oxide interface to the oxide scale/molten salt interface, thereby speeding up the oxide scale growth rate in terms of increasing the diffusion rate of metal cations and oxygen ions through the oxide scale. At the same time, the oxide scale adhesion is remarkedly improved because the metal vacancies at the oxide/alloy interface are filled by the newly formed oxide. After being treated by electrochemical oxidation, the corrosion rate of the Ni-16Fe-4Mo alloys in molten Li2CO3-Na2CO3-K2CO3 decreased ten-fold. Overall, electrochemical oxidation enables the rapid formation of an adherent and corrosion-resistant oxide scale on the metal substrate, offering a general and effective way to fabricate corrosion-resistant films to survive in various aggressively corrosive media.

Cyclic oxidation behavior of Pt modified NiCoCrAlYHfZr + AlNiY coating on a Ni-based single crystal superalloy

In this study, the NiCoCrAlY + AlNiY, NiCoCrAlYHfZr + AlNiY and Pt modified NiCoCrAlYHfZr + AlNiY coatings are prepared by combining arc ion plating (AIP), electroplating Pt and annealing treatment. All the coatings are composed of three different zones including an outer layer and an inner layer as well as an interdiffusion zone (IDZ), therein, the outer layer consists of β-NiAl phase with dispersed α-Cr phase and the inner layer is composed of NiCoCr-rich phase with dispersed β-NiAl phase. In addition, an Y-rich belt is formed between the outer layer and the inner layer. The cyclic oxidation behaviors of the three coatings at 1100 °C are investigated. Results indicate that Pt and Y-rich belt exhibit synergistic effect on preventing the interdiffusion between coating and substrate, thus a thinner secondary reaction zone (SRZ) forms in Pt modified NiCoCrAlYHfZr + AlNiY coating. The evolution processes of Y-rich belts in the three coatings are also discussed. Besides, a lower oxidation rate and enhanced oxide scale adherence are achieved in Pt modified NiCoCrAlYHfZr + AlNiY coating, the enhanced oxidation performance is mainly attributed to the co-segregation of Pt-Hf-Zr-Y at oxide scale grain boundaries and the synergistic effect of Pt-Hf-Zr-Y on suppressing interfacial voids growth.

Effect of copper on formation and adhesion of low carbon hot-rolled steel strips

The understanding of scales adhesively bonded requires several adhesion test method. Adhesion behaviour focuses on adhesive between scales-steel interface associated with scales formation and mechanical adhesion. This information on interface is typically obtained from tensile and pickling tests. Such information can give an indication of the adhesive strength of the interfaces. The hot-rolled low-carbon steel containing copper is focused on scales adhesion studies accomplished in laboratory. The key principle for good result is conception of an experimental method. Typical tensile testing machine equipped with a CCD camera has been adapted to investigate the scale failure. Classical gravimetric weight loss method has been conducted to assess corrosion rate. The scales morphology and cross-section of the samples are observed by scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). Phase identification is determined by X-ray diffraction (XRD). Much effort is needed to carefully assess scales adhesion. The test exposed the effect of copper composition selected to achieve hot-rolled steel properties on the formation and adhesion of oxide scales. Adhesive strength involves possible contributions from physical, chemical and mechanical. Characterisation of the scales-steel interface after the test would be much useful for exact investigation and still as a significant challenge. The experiment shows that element copper is already obvious at interface of relatively high levels of Cu of 0.225%. This effect is even decreased the adherence of oxide scales on the steel substrate by forming copper-rich phase at interface. Steel industry should more apply techniques such as tensile test for scales adhesion determination. This research is continuously looking for new method to assess scale adhesion. Consideration with results indicates that the element copper should more reasonably estimate for its effect to industrial descaling process.

Adhesion of thermal oxide scales on hot-rolled steels with 0.026 and 0.193 wt% Si in Ar-20 %H2O at 900 °C

The hot-rolled coil was widely used for forming steel products. The basic problem was that the scale formed on the steel will affect the surface quality of the product. The scale must be completely removed before moving on to the next process. Therefore, the objective of this research was to evaluate the adhesion of scale on the surface of the hot-rolled steel. The hot-rolled with 0.026 and 0.193 wt% Si-containing steels were used to oxidise in Ar-20 %H2O atmosphere at 900 °C for investigating scale adhesion. The scanning electron microscope and X-ray diffractometer were used for the analysis of physical and chemical characterisation. The scale adhesion can be observed using a tensile testing machine that has a CCD camera. The result shows that the thickness of hot-rolled steel with 0.026 and 0.193 wt% Si were 8.4 and 6.3 um respectively. The oxide scale was comprised hematite, magnetite, wustite and iron. The strain initiating the first spallation of scale on the 0.193 wt% Si steel was 5.59 % which was higher than the 0.026 wt% Si steel of 4.79 %. At this strain, the adhesion energy of scale on 0.193 wt% Si steel was 692 J m−2 and 673 J m−2 for 0.026 wt% Si steel. This reveals a greater scale adherence to the steel with higher Si contents. It suggests that silicon alloys may affect the adhesion behaviour of scale on a steel substrate. As a result, higher energy was required to remove scale before further processing.

Effect of Ce on microstructure evolution of oxide scale for CLAM steel exposed to LBE containing 10−6 wt% oxygen at 500 ℃

Lead-cooled fast reactor (LFR) is one of the six types of fourth-generation advanced nuclear reactors, and the corrosion with liquid lead-bismuth eutectic (LBE) to structural materials is regarded as a major obstacle restricting the development of LFR. This study focused on the surface morphology of oxide scale, aiming to illustrate the evolution law of oxide scale and the mechanism of Ce effect on oxide scale. China low activation martensitic (CLAM) and Ce-containing CLAM (Ce-CLAM) specimens generated roughly circular and slat-like magnetite islands respectively, but their magnetite pellets had similar growth trends from small to large sizes. Ce delayed the evolution of magnetite, enhanced the adhesion, continuity and integrity of oxide scale for Ce-CLAM specimen. The mechanism model of Ce effect on the evolution of magnetite and the scale growth model of the two kinds of specimens were proposed.

Analysis of the mechanism of chromatic aberration defects on A510L surface of high quality hot rolled pickled strip

In view of the chromatic aberration defects on the surface of hot-rolled strip A510L after pickling, the microscopic morphology features of different positions of the pickled strip surface were compared and analyzed by using laser confocal microscope (CLSM), and the generation mechanism of chromatic aberration defect was studied by using high-resolution scanning electron microscope and energy dispersive spectrometer (EDS). The results show that the main cause of surface chromatic aberration defects on the surface of pickling plate A510L is closely related to the interface state between hot-rolled raw material substrate and iron oxide scale, and there is an enrichment area of Fe2SiO4/FeO binary eutectic near the hot-rolled raw material substrate and iron oxide scale, and the proportion of Fe2SiO4 is higher as it approaches the strip steel matrix, and Fe2SiO4/FeO has a strong pinning effect, which leads to the adhesion of iron oxide scale. The existence of Fe2SiO4/FeO changes the structure of carbon steel iron oxide scale, which makes the bonding force between iron oxide scale and strip steel matrix increase the difficulty of pickling process, and finally presents the surface chromatic aberration defects after pickling.

Recrystallization mechanisms during high-temperature XRD and oxidation behavior of CNT-reinforced NiAl composites

In this study, a new perspective is presented on the CNTs-reinforced NiAl intermetallic composites, focusing on the influence of CNT addition on their high-temperature behavior. The obtained results revealed an effective grain boundary pinning effect of CNTs in hindering recrystallization and grain growth of the reinforced composites at high temperatures, leading to significantly smaller grain sizes. CNTs were observed to be beneficial for the high-temperature oxidation resistance at lower concentrations, but detrimental to the oxide scale adherence at higher concentrations. Subsequently, the NiAl-0.5CNT composites exhibited the lowest weight gain due to the stabilizing effect of carbon on the NiAl phase.

Effect of Zr and Ti on isothermal oxidation behavior of Nb–Si based alloys

The isothermal oxidation behavior of 56Nb-16Si-(20-x)Ti–3Cr–3Al-2Hf-xZr (x ​= ​0, 2, 5, 10 ​at. %) alloys was investigated at 800 ​°C and 1250 ​°C, respectively. The results show that increasing the Zr content evidently increased the oxidation rates at 800 ​°C, accompanied by the obvious occurrence of pesting oxidation. The alloys showed alike linear oxidation kinetics at 1250 ​°C. With the increase of Zr content, the adherence and integrity of oxide scales were improved, but the overall oxidation resistance was slightly deteriorated. The observed oxidation behavior may be attributed to the composition variation of Zr and Ti in the alloys. The oxidation mechanism associated with the composition variation is discussed in this study.

On the effect of oxide scale stability on the internal nitridation process in high-temperature alloys

AbstractInternal high-temperature corrosion of metallic materials is an important process often determining the service live of components used for high-temperature processes. As soon as a material looses the ability to form a dense and adherent oxide scale, non-metallic elements (e. g., O, N, C, and S) can diffuse from the atmosphere into the bulk material and react with alloying elements, forming different kinds of internal precipitates. The corrosion behaviour of two commercial alloys, Nicrofer 7520Ti and CMSX-4, and of the model alloy Ni – 20Cr – 6Ti was investigated in air and nitriding atmosphere at 1000 °C and 1100 °C under isothermal and thermal-cycling conditions. The study was performed using a continuous thermogravimetric method, which permits mass changes to be measured in different atmospheres and under thermal-cycling conditions. It was shown that damage in the oxide scale, caused by cracking or spallation, leads to an enhanced internal corrosion attack manifesting itself in the precipitation of oxides and nitrides. The experimental results were described in a mechanismbased approach by means of a simulation model that combines a numerical finite-difference treatment of the diffusion differential equations and the commercial thermodynamic program ChemApp. The model is able to predict the complex material behaviour during high-temperature exposure.