Cr2O3 Layer Research Articles

Corrosion Ferritic Stainless Steel in a Simulated Hydrothermal Liquefaction Bioconversion Aqueous Solution: Effect of Surface Cr Content

Abstract The objective of this study was to determine the effect of surface Cr content on the corrosion of ferritic stainless steels in hot pressurized alkaline water (310 °C at 10 MPa) simulating a hydrothermal liquefaction bioconversion medium. Two methods to increase the Cr surface content were investigated: (i) selecting commercial grades of ferritic stainless steel with an increasing Cr content and (ii) applying a Cr coating (chromizing) to a low-Cr (Type 409) ferritic stainless steel. The observed parabolic-like corrosion kinetics were analyzed and discussed in terms of the structure and composition of the double layered oxide films that formed. The (surface) Cr content is a critical factor affecting corrosion. Corrosion was reduced by 66% (after 20 days exposure) when increasing the Cr content from 9 wt.% (P91) to 21 wt.% (SS443) in the commercial grades of ferritic stainless steel. Moreover, corrosion was reduced by 84% (after 20 days exposure) by chromizing the surface of a low-Cr (Type 409) ferritic stainless steel. Improved corrosion protection was attributed to increased Cr incorporation into the inner (barrier) Fe(Fe1-nCrn)2O4 layer, with the formation of a Cr2O3 layer (resulting from chromizing) being most beneficial.

Synergistic effects of Pt and Y addition in (Ni, Pt)CrAlY bond coat on oxide spallation resistance and growth of interdiffusion zone between bond coat and Ni-based single crystal superalloy

This study shows the beneficial effect of Pt addition to the (β+γ)-NiCrAlY coating. Adding Y in NiCrAl increases oxide growth kinetics but improves spallation resistance. Pt with Y does not change the oxidation rate compared to only adding Y but significantly reduces spallation when cooled to room temperature. Continuous layers of Al2O3 and Cr2O3, along with other oxides such as YAlO3, NiCr2O4, and NiAl2O4, are observed. Moreover, Pt addition reduces the thickness of the interdiffusion zone where Al goes through an uphill diffusion profile, minimizing Al loss and significantly decreasing the growth of deleterious TCP phases.

The oxidation-dissolution behavior of Cr-coated Zr alloy in high temperature water

The corrosion and dissolution behavior of Cr-coated Zr alloy were investigated in high temperature water under varying dissolved oxygen (DO) and temperatures. Results demonstrate that the oxidation and dissolution rates of Cr coatings increase significantly with higher DO levels and temperature, while the Zr substrate remains unaffected by DO concentration. At DO levels below 10 ppb, Cr coatings exhibit high stability, but at 300 ppb DO, rapid corrosion/dissolution and spallation occur. The electrochemical potential (ECP) shifts in response to temperature and DO, driving the dissolution mechanism through three distinct region: steady-state, field-assisted dissolution (FAD), and complete dissolution. During the FAD period, a porous nanocrystalline Cr2O3 layer with residual Cr forms, characterized by non-uniform dissolution due to preferential oxidation at grain boundaries and microstructural defects. The soluble HCrO4− ions form at the base of the porous layer, followed by partial recrystallization at the surface, leading to the development of a thin Cr2O3 crystalline layer.

High-temperature oxidation behavior of GH4169 superalloy repair by wire-fed electron beam directed energy deposition

This study systematically examines the high-temperature oxidation behavior of GH4169 nickel-based superalloy repaired via wire-fed electron beam directed energy deposition (EB-DED). The analysis focuses on two distinct regions: the deposited zone and substrate zone. After exposure to 850 °C for 120 h, the oxidation films consisted of an outer layer of Cr2O3 and an inner layer of Al2O3 and TiO2. The deposition zone exhibits lower oxidation resistance, attributed to more pronounced element segregation resulting from the EB-DED process condition. This investigation establishes a clear correlation between element segregation and oxidation resistance, demonstrating that severe element segregation leads to poor oxidation resistance.

Cr2O3–NiO mixed oxides thin films for p-type transparent conductive electrodes

The Cr2O3–NiO mixed oxides’ thin films were formed by means of the layer-by-layer magnetron sputtering deposition of Cr2O3, NiO, and Cr2O3 layers on c-plane sapphire substrates. These thin-film structures, subjected to subsequent annealing, constituted a combination of the monocrystalline (0001) Cr2O3 and nonordered nickel oxide phase, which was a mixture of NiO and Ni2O3. The annealing at 900 and 1000 °С in air facilitated the diffusion of Ni and Cr atoms into the layers. Varying the annealing time allowed us to control the uniformity of the Ni and Cr distribution, the microrelief of the film surface, the transmittance in the visible region, and the sheet resistance of the Cr2O3–NiO thin-film structures. Thus, the films annealed at 900 °C during 30 min were characterized by a uniform distribution, a relatively weakly developed surface, a low sheet resistance, and the highest Haacke's Figure of Merit of 1.49 × 10–9 Ω–1. The formation of mixed Cr2O3–NiO oxides by the proposed approach was found to be an effective way to improve the performances of Cr2O3 based p-type transparent conductive electrodes.

Effect of grain size on high-temperature corrosion performance of laser cladding inconel 625 coating

As the calorific value of waste-to-energy incineration continues to rise, the corrosion damage to boilers becomes increasingly severe. The impact of the grain size on the high-temperature corrosion resistance of Inconel 625 coating was investigated. The results indicated that the corrosion performance of the coating in 1:1 NaCl–KCl salts at 700 °C for 120 h was highly dependent on the grain size of the coating. The coating fabricated with a laser power of 1800 W and an overlapping distance of 1.5 mm had an average grain size of 13.7 μm and highest hardness, exhibiting the best corrosion performance, with a corrosion weight loss of 1.4 mg/cm2. Coatings processed under different conditions all formed a three-layered structure, with a NiO outermost layer, a Cr2O3 intermediate layer, and an innermost Cr-depletion zone. Coatings with finer grains formed a continuous and dense protective oxide layer of NiO and Cr2O3 due to the rapid diffusion of alloy elements, effectively preventing the invasion of corrosive media and protecting the substrate from corrosion.

Minor tungsten addition enhances corrosive resistance in CoCrFeNi high-entropy alloy at elevated seawater temperature

Most research on the corrosive CoCrFeNi high-entropy alloy (HEA) has mainly modulated element species and atomic concentration recently. However, the corrosive resistance of the passive film in the elevated temperatures environment inevitably need to be extensively explored for application. In this work, the microstructure and corrosion behavior in the elevated temperatures of face-centered cubic (FCC) CoCrFeNiWx (x = 0 and 0.2) HEAs are investigated. The mechanism of passivation layers on the corrosion behavior of HEAs is further discussed for comparison to the alloy of addition tungsten. Through potentiodynamic polarization curves in 3.5 wt% NaCl solution from 25 °C to 70 °C, the addition of tungsten can raise the critical pitting temperature, while maintaining a lower passivation current density and a larger passivation range at the same time. The high resolution X-ray photoelectron spectrometer (HRXPS), electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) are all conducted to analyze the passivation composition and chemical reaction of the present alloys detailly. The CoCrFeNiW0.2 HEA exhibits the uniform Cr2O3 layer on the FCC matrix; the proportion of dispersive WO3 layer on the μ phase precipitates form a double-layer passive film under elevated temperature in 3.5 wt% NaCl. It shows that the synergistic effect of the double-layer passive film significantly enhances the pitting and corrosive resistance in this HEA.

Combating Cl− and SO42−-induced molten salt corrosion by laser cladding FeCrNiMoAl high-entropy alloy coating

FeCrNiMoAl high entropy alloy coating was successfully prepared by laser cladding method with phases of dominant face-centered cubic (FCC) and minor intermetallics (AlFe and AlNi). After 144 h of corrosion in the molten salt mixture of 40 % NaCl + 40 % KCl + 10 % Na2SO4 + 10 % K2SO4 at 600 °C, FeCrNiMoAl exhibited a much lower corrosion rate than conventional Inconel 625 by a reduction of 34 %. XRD and SEM were used to characterize the corroded samples. To combat Cl-induced active corrosion and S-induced sulfidation, Inconel 625 develops a single Cr2O3 layer while FeCrNiMoAl developed dual layers of outer Cr2O3 and inner Al2O3, which effectively prevents penetration of Cl and S.

Steam oxidation of thermally deposited coatings from 304 L and recycled 316 L/Z100 steels: Influence of temperature, coatings microstructure and steel recycling

The application of thermally sprayed stainless steels coatings is a well-established approach to protecting low-alloy steels against high-temperature degradation. In this study, we investigated both: (1) the influence of microstructural features of the coatings and (2) the recycling of stainless steels on the course of high temperature steam oxidation. It was achieved by thermally spraying coatings on C45 steel from 304 L and a new type of 316 L/Z100 steel, obtained as a result of mixed scraps recycling. Steam oxidation tests carried out in the temperature range 600–800 °C for 500 h in pure steam show temperature depended mechanism of oxidation, which was defined and described. The formation of the scales with a multi-layered structure was observed, consisting of Fe2O3, Fe3O4, Cr2O3, Fe- or Cr-rich CrxFex-2O3 and (Mn,Cr,Ni)xFe3-xO4 spinels. The relative ratio of the phases and their presence in particular scale layers varied depending on the material studied and the exposure temperature. The key findings are that recycling of steel deposited as protective coating has led to an unintended change in Si and C concentrations, which may affects course of oxidation. Also, the microstructure of the initial coatings, consisting of porosity and a significant volume of oxides formed during steel deposition, inhibits the formation of a homogeneous layer of protective Cr2O3. As a result, the established values of oxidation kinetics constants (in range of 8.55E-12 to 1.50E-10 g3·cm−6·s−1 for 316 L/Z100 and 2,71E-12 to 4.60E-10 g3·cm−6·s−1 for 304 L coatings) and oxidation activation energies (156.4 kJ·mol−1 for 316 L/Z100 and 211.5 kJ·mol−1 for 304 L coatings) differ significantly from those of bulk steels under the same conditions reported in the literature.

Effect of surface orientation on the corrosion behavior of Ni-based single-crystal alloy in a simulated marine atmosphere at 750 °C

DD5 single-crystal alloy samples with different surface orientations were obtained by machining the alloy ingot perpendicular (PP) and parallel (P), respectively, to its solidification direction (SD). The corrosion behaviors of the PPSD and PSD alloy samples were investigated in the atmosphere of moist air + NaCl aerosol at 750 °C. Results showed that during initial corrosion, γ′ phase developed a thin NiO layer with Al internal corrosion product. However, a NiO nodule with an internal Cr2O3 layer was formed on γ phase. As corrosion progressed, the corrosion product gradually grew to a NiO/(Al, Cr)2O3 bilayer, accompanied by internal corrosion consisting of Al2O3. It was also found that the PSD sample with a lower fraction and smaller size of γ’ phases exhibited better corrosion resistance than the PPSD sample. The effect of alloy surface orientation on the corrosion mechanism was discussed.

Reducing the oxidation rate of Cr-coated Zr alloys under high temperature steam environment: An approach of an outer Zr coating

Cr-coated Zr alloys are widely regarded as promising accident-tolerant fuel (ATF) cladding materials. However, the rapid consumption of the Cr coating through both oxidation and diffusion demands a thick coating, which is detrimental to neutron economic. In this study, a thin Zr coating was fabricated on the top of the Cr coating to act as a protective layer, aiming to reduce the oxidation consumption rate of Cr coatings. In-situ weight gain measurements were performed to determine the oxidation kinetics. The microstructural evolution of the coating/substrate interface and the oxide/coating interface were analyzed. The results show that the weight gain rate of the Zr-Cr coated Zr alloy sample is lower than that of the bare Cr-coated Zr alloy samples. An equiaxed grain structure composed of Cr/Zr mixed oxides was observed in the coating, which helps to inhibit elements diffusion and reduce the oxidation rate of Cr coatings. After steam oxidation at 1000 °C for 4 h, the sample structure consisted of the Zr substrate, a Cr2Zr layer, a residual Cr coating, a Cr2O3 layer, a Cr/Zr mixed oxides layer, and a ZrO2 layer.

Oxidized textured stainless steel surface with passivation layer as a high temperature selective solar absorber

A nanocrystalline textured stainless steel (SS) surface passivated with an AlCr oxide layer is proposed for use as a high temperature solar selective absorbers (SSAs). The textured SS surface was prepared by oxidizing in air at 800 °C for 30 min. The heating resulted in outward diffusion of the SS substrate Mn atoms, their oxidation on the surface, and formation of octahedral Mn3O4 nanocrystals, which play a role of textured surface. The passivation AlCr oxide single layer was deposited on the textured surface using reactive RF magnetron sputtering to protect the SS from further oxidation. The solar absorptivity αs and thermal emissivity ε298K of the as-deposited SSAs were 0.84 and 0.165, respectively. In order to study high temperature stability, SSAs were heat treated under air conditions at 600–900 °C for 0.1–300 h. SSAs demonstrated thermal stability at 600 °C for at least 300 h and degradation of optical properties with performance criterion PC < 0.05 at 700, 800, and 900 °C for 300 h, 30 h, and 1 h, respectively. The increase in thickness of the surface Cr2O3 layer on SS substrate was identified as the main degradation mechanism of SSA optical performance. SSAs demonstrated a high activation energy of 330 ± 30 kJ/mol. The obtained data can be used to design high temperature SSAs for concentrating solar energy systems operating under vacuum or air conditions at 500 °C.

Formation of pseudo-morphic domain in Cr2O3(0001) epitaxial film grown on α-Al2O3(0001) and its effect on Néel temperature

To address the issue of the impact of the epitaxial strain on the Néel temperature T N, we investigated the formation of the epitaxial domain in the Cr2O3 layer grown on the α-Al2O3(0001) substrate isostructural to Cr2O3 and determined T N of the fabricated films. We varied the sputtering power for the Cr2O3 growth from 10 W to 40 W to alter the strain condition of the epitaxial film. When the sputtering power is 10 W, the single epitaxial domain is formed, whereas the pseudo-morphic and relaxed domains coexist for the sputtering power above 20 W. T N decreased from about 271 K to below 252 K accompanied by the formation of the two types of epitaxial domains. The lattice parameters of the pseudo-morphic domain are beyond the elastic deformation approximation adopted in the theoretical approaches, suggesting that the correlation between the T N value and the microstructure also goes beyond the existing theoretical framework.

Oxidation behavior of Ni-20W and Ni-20W-20Cr heterogeneous seeds under different vacuum conditions

Since the oxide film on the surface of the heterogeneous seeds would usually cause the failure of the orientation control, the oxidation behavior of Ni-20 W and Ni-20 W-20Cr (wt. %) heterogeneous seeds under the different pressure was investigated in this work. The results showed that the thickness of the oxide layer thickness of the Ni-20 W heterogeneous seed in the atmospheric environment (1250 °C for 1 h) was about 133.1 μm, while that of the Ni-20 W-20Cr heterogeneous seed was near the 95.1 μm. The Cr element had greatly inhibited the penetration of the O2, and reduced the thickness of the oxides. However, the experiments conducted under low-vacuum conditions demonstrated that the surface of the Ni-20 W heterogeneous seed exhibited no significant oxides, while a layer of Cr2O3 was observed on the surface of the Ni-20 W-20Cr heterogeneous seed. Therefore, the oxidation thermodynamics for different elements was further calculated, and a different controlling factor of the oxidation under different environments was proposed.

High-temperature oxidation behavior of a novel γ′-strengthened superalloy manufactured by laser-beam powder bed fusion: Effect of post-heat treatment

This study systematically researched the high-temperature oxidation behavior of a γ′-strengthened alloy based on Haynes 230 prepared by laser-beam powder bed fusion (PBF-LB). The results indicate that the experimental alloy showed a higher oxidation resistance than Haynes 230 at 1000 °C. The oxidation products mainly consisted of the outmost MnCr2O4-TiO2 layer, intermediate Cr2O3 layer and inner TiO2 layer. Branched Al2O3 oxides were formed in the interior oxidation zone. Post-heat treatment can increase oxidation resistance by reducing the oxidation rates from 0.0152 mg2cm−4h−1 to 0.0126 mg2cm−4h−1. The decrease in dislocation density and the precipitation of ordered γ' phases can slow down the short-circuit diffusion and lattice diffusion rate of oxygen, and are the main reasons for this improvement. Furthermore, the γ' phase precipitation and dislocation density reduction can provide more sites for Cr2O3 nucleation and reduce the Cr supply required for grain growth. As a result, the Cr2O3 grains on the heat-treated sample surface were smaller.

Exploring the effect of Si content in Cr coating on its microstructure and properties

Four CrSi coatings with varying Si content ranging from 2 at.% to 9 at.% were deposited on the both surface of Zr-4 substrate. This study systematically investigated the effect of Si content on microstructure, mechanical properties, corrosion resistance and high-temperature oxidation resistance. Due to the lower Si content, only the Cr phase was detected in the CrSi coating, with Si existing in solid-solution. Therefore, all CrSi coatings exhibited good mechanical and hydrophobic properties. The addition of Si in the Cr coating significantly reduces the surface roughness compared with Cr coating. During the long-term autoclave test (30-day, 60-day and 90-day) at 320 °C and 11.3 MPa, CrSi coatings demonstrated superior corrosion resistance attributed to the effective inhibition of further Si dissolution by the dense and continuous Cr2O3 layer forming on the surface. Additionally, after exposure to high-temperature oxidation at 1200 °C for 30 min, all CrSi coatings protect the substrate from oxidation. However, only the Cr0.91Si0.09 coating internally formed a dense and continuous in-situ Zr2Si diffusion barrier layer, which effectively reduce the Cr/Zr inter-diffusion, and sufficient Si prevent the outwards diffusion of Cr by forming Cr3Si boundary. The corrosion and oxidation mechanism have been studied in detail.

Achieving enhanced strength-ductility and wear resistance in directed energy deposited super duplex stainless steel via inoculating NbN particles

In wire-based directed energy deposition (DED), super duplex stainless steel (SDSS) typically encounters issues including coarse grains, a contradictory relationship between strength and ductility, and inferior wear resistance properties. Herein, we report the introduction of micron-sized NbN particles into DEDed SDSS to achieve an optimized combination of fine microstructure, high strength, impressively larger ductility and better wear resistance. During the DED process, NbN inoculant dissolves and re-precipitates, forming fine NbN and σ particles around 100 nm in size. These NbN particles act as nucleation sites for equiaxed grains, refining both ferrite and austenite. In addition, Nb and N elements left from NbN dissolution enhance the solution strengthening effect. These factors collectively boost hardness and strength in DEDed SDSS. Furthermore, the high Nb level in DEDed SDSS facilitates a dense Cr2O3 layer formation on the specimen surface during wear tests, enhancing wear resistance. Increased Nb and N also lower stacking fault energy (SFE) of SDSS austenite, promoting the occurrence of deformation twinning, and the improvement of work hardening and ductility during plastic deformation. This work shows the great potential of wire-arc DED technology to fabricate SDSS with unique microstructures, excellent wear resistance, and an exceptional combination of strength and ductility for practical applications.

Effect of Cr on high-temperature oxidation resistance of Cr–Si–Mn alloyed press-hardened steel during press hardening

It is of great interest to overcome the problem of high-temperature oxidation of press-hardened steels (PHS) in press hardening with a cost-effective Cr alloying strategy. Therefore, since Cr is one of the expensive metals, the effect of Cr (Cr ≤ 3 wt%) content on the oxidation resistance of Cr–Si–Mn alloyed steels was investigated. It was found that Cr–Si–Mn alloyed PHS with a Cr content of about 1.5 wt% or less cannot form a continuous Cr2O3 layer during press hardening. However, when the Cr content reaches around 2.5 wt%, the PHS shows excellent oxidation resistance due to the formation of continuous Cr2O3 and amorphous SiO2 layers, as well as an Mn-rich oxide layer. However, further addition of 0.5 wt% could not significantly improve the oxidation resistance of this PHS. Moreover, the increase in Cr content simultaneously enhances the positive role of Si and Mn in high-temperature oxidation resistance. This work provides new insights into the design of the next generation of PHSs with economical and superior performance.

Investigation of High-Temperature Oxidation Behavior of Additive Manufactured CoCrMo Alloy for Mandrel Manufacturing.

The cyclic oxidation behavior of an additive manufactured CoCrMo alloy with 0.14 wt.% C was investigated at 914 °C for 32 cycles, each lasting 10 h, resulting in a total exposure time of 320 h. The oxidation rate was assessed for mass gain after finishing each 40 h oxidation cycle. It was experimentally determined that the oxidative process at 914 °C of this CoCrMo alloy follows a parabolic law, with the process being fast at the beginning and slowing down after the first 40 h. The microstructural analysis revealed that in the as-printed state, the phases developed were primarily the γ matrix and minor traces of ε phase. The oxidative process ensured an increase in the ε phase and precipitation of carbides which produced a 12% increase in the material's hardness after the first 40 h of exposure at 914 °C. The oxidation process led to the development of an oxide scale comprising a dense Cr2O3 layer and a porous layer of CoCr2O4 spinel, the latter spalling after the 240 h of exposure. Despite this spallation, the oxide scale continued to develop in the presence of O, Cr, and Co. The experimental analysis provided valuable insights regarding the material's behavior under prolonged exposure at high temperature in air, demonstrating its suitability as a candidate for additive manufactured mandrels used for bending metallic pipe fitting elbows.

X‐ray standing wave assisted XANES for depth dependent chemical state analysis of Cr in Cr2O3/Cr bilayer structure

We report the detailed depth‐dependent structural and chemical analysis of the Cr2O3/Cr bilayer structure deposited on Si ˂100˃ substrate. The non‐destructive simultaneous X‐ray reflectivity and grazing incidence X‐ray fluorescence measurements were used for this purpose. Corresponding variation in the chemical state of Cr atoms as a function of depth has been studied using X‐ray standing wave (XSW) assisted X‐ray absorption near edge structure (XANES) measurements. Various oxidation states of Cr atoms present in the Cr2O3/Cr bilayer structure were determined using X‐ray photoelectron spectroscopy (XPS). Depth‐resolved XANES measurements confirmed the presence of chromium oxide (Cr2O3) and hydroxide (Cr (OH)3) at the top surface of the Cr2O3/Cr bilayer structure. The results also reveal the presence of metallic Cr along with its compounds Cr2O3 and Cr (OH)3 at the interface medium, showing significant mixing between the Cr2O3 and Cr layers. Our results clearly demonstrate that the XSW assisted XANES technique is extremely efficient for determining the variation of chemical states at the surface, interface, and different depths of a thin film structure. Such types of analysis are particularly useful for differentiating the presence of a metal from its own oxides, even at higher depths inside a thin film medium.