Oxide Scale Adherence Research Articles

Effects of Long‐Term Ageing at High Temperatures on Oxide Scale Development and Evolution of Austenitic Steels Microstructure

This study is conducted to investigate the effects of long‐term air oxidation on the microstructural stability of HR3C, HR6W, and Sanicro 25 stainless steel. The materials are exposed to air atmosphere for 1000 and 10 000 h at 650, 700, and 750 °C respectively. The postexposed materials indicate some microstructural changes: the HR3C stainless steel develops Fe–Cr‐rich oxide scale, whereas HR6W steel forms a brittle, low adherent oxide scale consisting different concentrations of Cr, Mn, Fe, and Ni. Finally, Sanicro 25 stainless steel promotes the formation of a homogeneous‐rich Cr oxide scale at high temperatures. The analyses are performed using scanning electron microscopy (SEM)/energy‐dispersive X‐ray spectrometry (EDS) and X‐ray mappings.

Solid state interfacial reactions in a ceria-coated Ni-based superalloy

Perovskite type phases are known to improve the adherence of protective oxide scales grown onto chromia- and alumina-forming alloys and coatings. The present study investigates the interfacial reactions occurring during the high temperature oxidation of a ceria coated Ni-based superalloy at 1100 °C. The substrate firstly grew a duplex oxide scale with a NiAl2O4 spinel on top of an α-Al2O3 scale underneath the ceria coating. Increasing oxidation time led to the development of Al-rich and Ce-rich nanometric grains at the oxide scale/coating interface and to the progressive vanishing of the NiAl2O4 spinel. Micro-Raman analyses demonstrated the formation of cerium aluminate CeAlO3 by solid-state reaction between Al2O3 and CeO2 favoured by an Al supply coming from the substrate. The results are in line with the thermodynamic calculations.

In-situ interfacial tribochemistry toward eliminating red-scale of silicon steel in friction process

Abstract Irregularly striped red-scale defects are often formed on hot rolled silicon steel strips, and some still remain on the surface even after pickling. In this study, an in-situ interfacial tribochemistry concept was proposed to eliminate red-scale silicon steel using ball-on-disc test, by transforming harder eutectic Fe2SiO4/FeO eutectic into other compounds with sodium polyphosphate lubricant. The results show that polyphosphate can lubricate the high speed steel/silicon steel interface effectively with significant reduction of the friction and wear by 50% and 90% respectively. And in situ formed compounds of Na3Fe2(PO4)3 and NaFePO4 at the rubbing interface can eliminate red-scale on silicon steel by weakening the adhesion of oxide scale to the substrate.

Oxidation Behavior of Oxide Dispersion-Strengthened W–Ni Alloys

Oxidation behavior (at 1000 °C for 10 h) of 1.0 wt% oxide dispersion-strengthened (nano-Y2O3, Al2O3, La2O3 dispersed) mechanically alloyed (10 h) and sintered (1400 °C, 1500 °C, 2 h) W–Ni alloys has been investigated. Oxidation significantly constrains the application window of W and therefore needs to be counteracted by suitable alloying and dispersion. W–Ni–Y2O3 alloy possesses excellent oxidation resistance at the high sintering temperatures. Moreover, W–Ni–Al2O3 sintered at 1400 °C exhibited no spallation or blistering after 10 h of oxidation. The enhanced oxidation resistance of W–Ni–Y2O3 alloy is attributed to superior densification, oxide-scale adhesion with the matrix phase, reduced volatilization of WO3 owing to NiWO4 and enhanced concentration of Y ions enriched with oxide. The investigation will provide a strategy to fabricate oxidation-resistant alloys by oxide dispersion for high-temperature applications.

Stress and Adhesion of Protective Oxide Scales on Stainless Steels and RE Effects

Stress and Adhesion of Protective Oxide Scales on Stainless Steels and RE Effects

Temporal evolution, coarsening behavior and oxidation resistance of Ni–15Al superalloy

The temporal evolution including size, amount, morphology and distribution of γ′ precipitates in γ matrix in conjunction with coarsening kinetics and oxidation behavior of a model Ni–15Al alloy aged at 800 °C for 1, 4, 16, 64 and 256 h is studied in detail. The microstructure of the investigated samples consists of L12-type ordered γ’ (Ni3Al) precipitates and a disordered Ni-rich γ (FCC) matrix phase. Spheroidal-to-cuboidal-to parallelpipedic morphological transition is observed as the mean precipitate radius increases with increasing aging time. The temporal exponent p is calculated as 0.35 which agrees well with the diffusion-controlled LSW theory (p = 0.33) for coarsening of a binary alloy. However, the power law dependence of the number density (NV) departs from the theoretical predictions which suggests a quasi-stationary coarsening. The cyclic oxidation behavior of as-cast and aged (800 °C for 4, 16, 64 and 256 h) Ni–15Al superalloys at 1000 °C in laboratory air were investigated in detail. The results showed that 4 and 16 h aged samples exhibited considerably better oxidation resistance compared to as-cast and 64 and 256 h aged samples. The oxide product is identified as NiO by X-ray diffraction (XRD) analyses. Uniform, even and adherent oxide scale formed without any void formation and important scale spallation.

High-temperature performance of (Ni,Pt)Al coatings on second-generation Ni-base single-crystal superalloy at 1100 °C: Effect of excess S impurities

Acidic and basic single-phase β-(Ni,Pt)Al coatings were prepared by Pt electroplating (employing acidic and alkaline Pt-plating baths, respectively) and gaseous phase aluminizing. In both isothermal and cyclic oxidation tests at 1100 °C, the acidic (Ni,Pt)Al coating showed inferior oxidation resistance compared to the basic coating. The poorer oxidation performance and higher scale spallation tendency of the acidic (Ni,Pt)Al coating was attributed to the presence of excess S, which deteriorated oxide scale adherence by promoting the formation of pores and cracks under Al2O3 scale. The void formation mechanism and detrimental role of excess S in state-of-the-art Pt-modified aluminide coatings are discussed.

On the hot-rolled recycled carbon steels: their oxide formation, pickling ability and scale adhesion

Purpose The purpose of this study is to investigate the formation, pickling ability and adhesion of thermal oxide scales on the hot-rolled recycled steels produced from the medium and thin slabs. Because the scale on the steel produced from the medium slab was relatively thick of about 11 µm, it contained cracks after hot-rolling. Thus during pickling, the scale was uniformly attacked with the simultaneous dissolution of the inner scale because of the penetration of acid through cracks. However, the scale on the steel produced from the thin slab was thinner of about 6 µm and thus, nearly crack-free. The pickling solution thus attacked the scale surface uniformly. At longer pickling periods, pits were also nucleated and propagated. Concurrently, the tensile testing machine with a CCD camera has been applied to observe scale adhesion. Design/methodology/approach The formation, pickling ability and adhesion of thermal oxide scales on the hot-rolled recycled steels produced from the recycled slab, e.g. medium slab and thin slab, were investigated. The morphology and phase identification were examined by using scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Furthermore, the adhesion behaviour of oxide scale was investigated by immersion test and tensile test with a CCD camera. Findings For the scale formation, it was found that the hematite and magnetite were formed on the hot-rolled recycled steels produced from the medium and thin slabs. For the immersion test, it was found that the scale on hot-rolled recycled steels produced from the medium slab was more difficult to be pickled as represented by the longer time for the complete pickling. This was consistent with the result of tensile test; the steel produced from the medium slab had better scale adhesion as represented by the higher strain initiating the first spallation of scale. Originality/value The effects of slab types and its alloying element were investigated to understand the scale adhesion behaviour. The empirical pickling mechanisms and the mechanical adhesion energy were proposed. It led to the understanding in the control of alloying element in the hot-rolled steel.

Adhesion, friction and wear analysis of a chromium oxide scale on a ferritic stainless steel

The aim of this study is to explore the potential engineering application of a thermally grown chromium oxide scale on a ferritic stainless steel. The friction and wear behaviour of the oxide scale were investigated by scratch and pin-on-disk tests. The failure mechanisms of the oxide scale subjected to scratch tests under both progressive and constant loading were investigated. It shows that the oxide scale adheres well to the steel substrate and is in a ductile failure. The oxide scale leads to an increase in the coefficient of friction (COF) under different constant loads when compared to what occurs when there is no oxide scale in the scratch test. The pin-on-disk tribological tests show that the chromium oxide scale on the ferritic stainless steel causes abrasive wear of the high-speed steel (HSS) pin, but it enhances the wear resistance of the ferritic stainless steel disk. The COF is slightly lower when there is oxide scale on the disk which is different from that by the scratch test. The ferritic steel substrate fine wear particles generated during the dry sliding and the formation of new compound layers on the surface can stabilise the COF. The wear mechanism is proposed and the tribological properties of the thermally grown chromium oxide by the two techniques are discussed.

Evaluation of rare‐earth element dopants (Sm and Er) on ablation resistance of ZrB2/SiC‐sintered billets

AbstractIn this paper, how rare‐earth element dopants (samarium and erbium) affect the scale development of sintered ZrB2/SiC (ZBS) samples during ablation testing was investigated. ZBS billets with five different Sm to Er ratios, with a nominal total amount of 3 mol% dopant incorporated, were prepared by sintering in vacuum to 2000°C and subjected to 60 and 300 seconds ablation cycles. Differences in surface temperatures between ZBS samples with different dopant ratios suggests differences in spectral absorptance/emittance between each of the five compositions investigated. ZBS billets co‐doped with Sm and Er form a beneficial c1‐(Sm/Er)0.2Zr0.8O1.9 oxide scale as the majority phase, with some glassy phase observed. The crystalline c1‐(Sm/Er)0.2Zr0.8O1.9 oxide scale is more thermally stable than the m‐ZrO2 oxide scale typically formed in oxidized ZBS systems, resulting in a more adherent oxide scale to the unreacted material. The crystalline oxide scale and the amorphous phase are formed by a convection cell mechanism where the c1‐(Sm/Er)0.2Zr0.8O1.9 crystalline islands precipitate, grow, and coalesce.

Hot Corrosion Resistance of Hot-Dip-Aluminized AISI 321 Stainless Steel in a Salt Mixture of 60%V2O5 + 40% Na2SO4 at 700 °C

Hot-dip aluminizing (HDA) is an established surface coating technique to deposit aluminium on ferrous substrates. The aluminium deposit forms a compact layer of alumina when exposed to high temperature, providing high-temperature oxidation and corrosion protection. In the present investigation, HDA of AISI 321 stainless steel was carried out in pure aluminium bath at 700 °C. The steel samples were dipped in molten Al bath for 10 min. The HDA sample was given diffusion treatment at 900 °C for 5 h before subjecting to hot corrosion tests. The microstructural features after hot corrosion tests were analyzed using an X-ray diffractometer and a scanning electron microscope. The aluminized and bare steel samples were subjected to hot corrosion test in a salt mixture of 60%V2O5 + 40% Na2SO4 at 700 °C. The tests were conducted for 50 cycles, of which each cycle consisted of 1-h heating at 700 °C in furnace followed by 20-min cooling in air. The corrosion kinetics was studied by thermogravimetric analysis. The study revealed that weight gains for aluminized sample were lower than the uncoated sample. The weight gain for the uncoated sample at the end of 50 cycles was 5.87 mg/cm2, and that of the aluminized sample was 2.3 mg/cm2. Spalling of oxide scales was observed for the uncoated sample, while aluminized sample showed adherent oxide scales resulting in increased hot corrosion resistance.

Effects of tungsten content on the high-temperature oxidation behavior of Ni-xW-6Cr alloys

The oxidation of Ni-(5–30 wt.%) W-6 wt.% Cr alloys was studied at 850 °C in air, among which Ni-25 W-6Cr alloy shows the best oxidation resistance. Because W acts as secondary getter, an external continuous oxide scale (NiCr2O4) is formed, which is responsible for the excellent oxidation resistance of these alloys. When the W content reach above 25 wt. %, the excessive W can facilitate the growth of CrWO4, preventing the formation of NiCr2O4, and breaking the continuity of the chrome oxide scale. Additionally, NiWO4 formed near the metal-scale interface can weaken the adhesion of oxide scales, causing cracks.

Effect of Rolling Reduction and Temperature on the Oxide Scale of Hot Rolled Mild Steel Strip

Hot rolling experiments were designed to investigate the effect of rolling temperature and rolling deformation on microstructure, thickness and surface red scale of hot rolled mild steel oxide scale by spectrometer, SEM and pickling experiment. The research results show that in the same other experiment conditions, the greater the rolling deformation, the thinner the oxide scale extend; with the increase of rolling temperature, the plasticity of oxide scale is enhanced, the oxide scale can be compacted under a larger rolling reduction, which increase the adhesion of oxide scale to substrate and reduce the oxide scale falling off. The higher rolling temperature is, the greater the allowable critical deformation to inhibit red scale is, and the thicker tolerable thickness of the initial oxide scale is. In the process of hot strip rolling, improving rolling load distribution of the front frame and reducing the rolling deformation of the tail frame is helpful to control strip red scale and make oxide scale deform uniformly.

Effect of SiO2 Dispersion on Chlorine-Induced High-Temperature Corrosion of High-Velocity Air-Fuel Sprayed NiCrMo Coating

NiCrMo coatings with and without dispersed SiO2 were deposited using high-velocity air-fuel technique. Thermogravimetric experiments were conducted in 5% O2 + 500 vppm HCl + N2 with and without a KCl deposit at 600°C for up to 168 h. The SiO2-containing coating showed lower weight change as a result of formation of a protective and adherent Cr-rich oxide scale. SiO2 decelerated short-circuit diffusion of Cr3+ through scale’s defects, e.g., vacancies, and promoted the selective oxidation of Cr to form the protective Cr-rich oxide scale. Furthermore, the presence of SiO2 led to less subsurface depletion of Cr in the coating, and accordingly less corrosion of the substrate. The formed corrosion product on the SiO2-free coating was highly porous, non-adherent, and thick.

The Cross-Sectional Investigation of Oxide Scale FeCr Alloys and Commercial Ferritic Steel Implanted with Lanthanum and Titanium Dopants after Oxidation Test at 900°C

The cross-sectional examinations of oxide scales formed by oxidation on the surface of FeCr alloys and Ferritic Steel that implanted with lanthanum and titanium dopants were observed and investigated. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) has been used to study the cross-sectional oxides produced by specimens after oxidation process. X-ray diffraction (XRD) analysis was used to strengthen the analysis of the oxide scale morphology, oxide phases and oxidation products. Cross-sectional observations show the effectiveness of La implantation for improving thinner and stronger scale/substrate interface during oxidation process. The result shows that the thickness of oxide scales formed on the surface of La implanted FeCr alloy and ferritic steel was found less than 3 µm and 300 μm, respectively. The oxide scale formed on the surface of La implanted specimens consisted roughly of Cr2O3 with a small amount of FeO mixture. The oxidation resistance of FeCr alloy that implanted with Lanthanum showed better quality than that of commercial alloy. The beneficial effect of La implanted sample on the oxidation resistance was clearly visible to improve the adherence of oxide scale. Cross-sectional observations revealed the effectiveness of La implantation for improving thinner and stronger scale/substrate interface during oxidation process which presents the homogenous structure with good adherence and a uniform inter-diffusion layer between substrate and oxide layer.

Cyclic oxidation behavior and oxide scale adhesion of Al/NiCrAlY coating on pure titanium alloy

Al and Al/NiCrAlY coatings were deposited on pure titanium substrate by air plasma spraying method. Cyclic oxidation behavior and oxide scale adhesion at 800 °C for 100 cycles were investigated. For the single Al coating, a severe spalling of oxide scale and elemental interdiffusion occurred after 100 cycles. The mass loss of the single Al coating has reached to 1.39 mg/cm2. The oxide scale on the duplex Al/NiCrAlY coating kept a good bonding with the underlay coating. The addition of NiCrAlY layer inhibited the outward diffusion of Ti atoms and inward diffusion of Al atoms. The propagation of cracks and the formation of pores were also suppressed by NiCrAlY layer. As a result, the duplex Al/NiCrAlY coating possessed a superior cyclic oxidation resistance.

Corrosion of Carbon Steel with and without Aluminized Coating in (O, S, H)-containing Gases at 500-800℃

The carbon steel formed the thick, somewhat porous, loosely adherent iron oxide scale when oxidized at 500-800℃ for 15 h in air. It formed the thicker, more porous, nonadherent scale consisting of FeS plus iron oxides in Ar/1%SO₂-mixed gas. It formed the much thicker, more porous, nonadherent scale consisting of FeS plus iron oxides in Ar/0.1% H₂S-mixed gas. However, the aluminized carbon steel formed the thin, protective Al₂O₃ surface scale even in Ar/1%SO₂-, and Ar/0.1%H₂S-mixed gas. Aluminizing drastically improved the corrosion resistance in (O, S, H)-containing gas.

Relation between microstructure induced by oxidation and room-temperature mechanical properties of the thermally grown oxide scales on austenitic stainless steels

The spalling/cracking behaviour, at room temperature, of thermally grown oxide scales under tensile stress was investigated using SEM in-situ tensile testing for two austenitic stainless steels with close composition except their S content. A correlation between damage patterns, microstructure, mechanical and adhesion properties of the oxide scales is proposed. The difference in microstructure evolution during oxidation between the two steels is explained in relation with the volume fraction of MnS inclusions in the substrate (i.e. S content). Although a direct effect of S content on the oxide scale adhesion is not evidenced, the metal/oxide toughness seems strongly affected by oxides features such as scale thickness, Fe content and location of internal oxides (SiO2 along the metal/scale interface or at the grain boundaries of the underneath substrate).

High Temperature Oxidation of Micro-alloyed Steel and Its Scale Adhesion

The present work investigated the high temperature oxidation behaviour of the micro-alloyed steel and the adhesion of thermal oxide scale to its steel substrate. Oxidation testing was conducted at 815 °C in oxygen without and with 17.9% v/v water vapour. The oxidation kinetics in the two atmospheres were parabolic with similar rate constants, i.e. 1.13 × 10−9 and 1.17 × 10−9 g2 cm−4 s−1 for the sample oxidised in oxygen without and with water vapour, respectively. The XRD peaks for wustite, magnetite, Ti-doped magnetite and titanium carbide were detected for the sample oxidised in oxygen. For the sample oxidised in the humidified atmosphere, Ti-doped magnetite was dominantly observed, additionally with titanium carbide. A tensile testing machine equipped with an optical lens was used to monitor scale failure during straining. For the sample oxidised for 1 min, the strain initiating the first spallation of the steel oxidised in the humidified oxygen was 1.74 ± 0.14%. This strain was higher than the strain initiating the first spallation of the steel oxidised in oxygen which was 1.00 ± 0.04%, indicating the improved adhesion of scale formed in the atmosphere containing water vapour. Mechanisms of water vapour effect on scale adhesion are discussed.

引張試験によるスケール密着性評価

引張試験によるスケール密着性評価