Outer Oxide Research Articles

Revealing the complexity of high temperature oxide formation in a 38Ni-21Cr-20Fe-13Ru-6Mo-2W (at. %) multi-principal element alloy

The oxide film formed on a corrosion-resistant multi-principal element alloy 38Ni-21Cr-20Fe-13Ru-6Mo-2W (at. %) was characterized via transmission electron microscopy and atom probe tomography. Oxidation in air at 600°C for 1080 minutes resulted in a complex, layered film with multiphase inner and outer oxide scales, and localized recrystallization in the underlying base alloy. The outer oxide scale is dominated by two phases: a Ni-Fe spinel (≈NiFe2O4) and a Ni-rich monoclinic phase (NiMoO4). The inner oxide consists of a near surface Ni-Fe-Cr spinel and RuO2, and semi-continuous Cr2O3 with oxygen-rich Ru-Mo metal inclusions. Local recrystallization and concomitant elemental partitioning in the base alloy was influenced by a high dislocation density in the as-prepared sample surface.

High-Temperature Oxidation Performance of 4Cr4Mo2NiMnSiV Hot Die Steel

A new type of hot working die steel was designed by using JMatPro, and high-temperature oxidation tests were carried out in the ambient atmosphere at 600 ℃ and 700 ℃. The heat treatment process and oxidation mechanism of the designed 4Cr4Mo2NiMnSiV steel were studied in detail. XRD, SEM and EDS were used to analyze the crystallographic phases, surface and cross-section morphologies of the oxide films. The results show that the main phases in the 4Cr4Mo2NiMnSiV steel were γ and α + δ. During the high-temperature oxidation, oxidation of the Fe outer layer and Cr inner layer occurred. After oxidation at 600℃, the surface oxidation layer comprised a monolayer with an uneven morphology. The surface oxide film had two layers after oxidation at 700℃. The outer oxide layer mainly contained Fe2O3 and Fe3O4, while the inner oxide layer mainly contained Cr2O3. The microstructure was relatively regular and had a significant effect on the protection of the metallic matrix. When oxidized, the 4Cr4Mo2NiMnSiV alloy steel easily formed protective layers, such as Cr2O3 and SiO2, so that the test steel had excellent oxidation resistance at high temperatures.

Effect of Tensile Stress on the Oxide Properties of a Nickel-Based Alloy 600 in Simulated PWR Secondary Water.

The purpose of this work was to examine the effect of tensile stress on the oxide properties of a nickel-based Alloy 600 that was exposed to simulated nuclear steam generator water at 340 °C for 1000 h. The size of the outer oxide particles increased, and the chromium content of the inner oxides decreased under tensile stress. Electrochemical measurements revealed that the charge carrier density increased, and the charge transfer resistance and film resistance were reduced under the tensile stress condition. These changes in the oxide properties are attributed to the formation of short diffusion paths such as line and surface defects due to tensile deformation.

High temperature and short-term oxidation behavior of CoCrCu1.2FeNi high entropy alloy in solid and semi-solid state

The short-term oxidation behavior of CoCrCu1.2FeNi high entropy alloy in solid and semi-solid state was investigated. Except for the two-stage parabola characteristic at 1340 ℃, the oxidation kinetics of other temperatures showed single-stage parabola characteristic. The oxidation products and oxide scales were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersion spectrum (EDS). During solid oxidation, the oxide scales were composed of outer oxide layer (CuO and Cu2O) and inner oxide layer (Co, Cr, Fe, Ni3O4) spinel oxides. During semi-solid oxidation, internal and external diffusion was significantly enhanced, liquid flow and holes became diffusion channels.

Degradable and self-luminescence porous silicon particles as tissue adhesive for wound closure, monitoring and accelerating wound healing

Tissue adhesives have received much attention for their effectiveness in sealing wounds or incisions in clinical surgery, especially in minimally invasive surgery. To meet the safe and smart wound management requirements, ideal tissue adhesives are expected to have high biocompatibility, and be able to accelerate wound closing and healing, and monitor wound healing process. However, few adhesives fit all of the above descriptions. It has been demonstrated that inorganic nanoparticles can directly glue biological tissue based on nano-bridging effect. In this study, self-luminescence porous silicon (LPSi) particles were prepared with degradable and biocompatible properties. In addition, the self-luminescence property of LPSi particles was discovered by In Vivo Imaging System (IVIS) for the first time, which can avoid the limitations of photoluminescence imaging. Due to the oxidation and degradation reaction, LPSi particles not only can be degraded completely in several days, but also showed satisfactory biocompatibility. And their degradation product could promote tube formation of HUVECs. Moreover, owing to the high specific surface area and the outer oxide layer of LPSi particles, LPSi tissue adhesive exhibited strong adhesive strength to pig livers. Furthermore, this adhesive closed wound rapidly, promoted angiogenesis and epidermal regeneration, and facilitated wound healing in a mouse skin incision model. Importantly, the wound healing ratio can be monitored by measuring the self-luminescence intensity of LPSi particles in the wound site. This study reveals that LPSi particles could be employed as a safe and smart wound management tissue adhesive for wound closure, as well as accelerating and monitoring wound healing.

Modification of the Mechanical Properties of Core‐Shell Liquid Gallium Nanoparticles by Thermal Oxidation at Low Temperature

AbstractGallium nanoparticles (Ga NPs) are attracting increasing attention because of their appealing physical‐chemical properties. In particular, their mechanical properties play a key role in the implementation of these core‐shell structures on certain applications, such as soft and stretchable electronics. Thus, efforts are being addressed to modulate them mainly by chemical means. In contrast, this study investigates how the mechanical properties of the outer gallium thin oxide shell change when its thickness is increased through a thermal oxidation strategy. Specifically, as‐deposited Ga NPs, as well as those subjected to thermal oxidation at 300 °C for three different times, are studied by performing single‐particle indentations by atomic force microscopy over a wide range of NP radius. This analysis helps to confirm that the Reissner's thin‐shell model for small deformations within the elastic regime is obeyed. From these data, the dependence of the shell stiffness and the Young's modulus of the gallium oxide on the thermal treatment is obtained. It is found that the shell stiffness increases with the annealing time, even by a factor of 50 under prolonged thermal oxidation, while the gallium oxide Young's modulus, close to 30 GPa, does not change significantly.

Oxidation Behavior and Oxide Transformation of a Pt-Modified Aluminide Coating at Moderate High Temperature

The oxidation performance of a single-phase Pt-modified aluminide coating was assessed in oxidation test at 980 °C in comparison with the single crystal superalloy. The results suggested that the Pt-modified aluminide coating exhibited superior oxidation resistance. During oxidation, the oxide scale formed on bare alloy changed constantly followed by the constitution of the multi-layer scale structure: An outer scale mainly consisted of Cr2O3 + NiCr2O4 + TiO2 with scarce protection, and an internal scale mainly consisted of Al2O3. The thickness of the outer oxide scale increased with time, where the scale became looser and more porous. Meanwhile, the internal scale was discontinuous. Oxygen and nitrogen inwardly diffused into substrate, forming Ta2O5 and TiN particles. In contrast to the complex constitution of oxide scale, a uniform and continuous Al2O3 scale formed on Pt-modified aluminide-coated samples after oxidation at 980 °C for 1500 h, which showed no spallation and cracking. Interestingly, θ-Al2O3 and α-Al2O3 phases remained after such a long oxidation time. It is the relatively lower temperature and the presence of Pt retarded θ-α transformation. The degradation rate from β-NiAl to γ′-Ni3Al was very slow in the coating. The various development of oxide scale on the coating and substrate was individually studied.

Effect of helium ion irradiation on short-time corrosion behavior of two novel high-entropy alloys in simulated PWR primary water

The effect of helium ion irradiation on the short-time corrosion behavior of two novel high-entropy alloys (HEAs) was investigated in simulated PWR primary water. The results revealed that a double-layer oxide film consisting of Ti, Nb and V oxides was formed on both HEAs, including outer oxide particles and a protective inner oxide layer with a maximum depth of ∼500 nm. Irradiation up to 10.5 dpa may hardly promote corrosion kinetics since severe lattice distortion and sluggish diffusion in HEAs. The corrosion processes with and without irradiation were discussed in detail.

FeCrMoWCBY metallic glass with high corrosion resistance in molten lead–bismuth eutectic alloy

The FeCrMoWCBY metallic glass exhibited excellent corrosion resistance in oxygen-saturated lead-bismuth eutectic (LBE) at 500 °C. The corrosion resistance could be enhanced by adding an appropriate amount of W element, while excessive W deteriorated the corrosion resistance of the metallic glass. The surface of the Fe-based metallic glass was composed of an inner amorphous transition layer and outer FeCr2O4 oxide nanocrystal layer. The continuous amorphous transition layer acted as a diffusion barrier layer to prevent further corrosion of the metallic glass.

Transformations of Ti-5Al-5V-5Cr-3Mo powder due to reuse in laser powder bed fusion: A surface analytical approach

Reactive Ti-5Al-5 V-5Cr-3Mo (Ti5553) alloy feedstock powder is used in laser powder-bed fusion (LPBF). Due to the large quantity of powder necessary for LPBF, powder is reused numerous times under oxidizing environments. Transformations to the powder’s native surface oxide may impact the LPBF process and lead to deviations from expected behavior of printed parts.Here, we present a multimodal characterization of new and reused powder by combining X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and transmission electron microscopy (TEM) of focused ion beam (FIB)-prepared cross sections of individual powder particles to understand how the surface oxide composition changes, grows, and becomes hydroxylated and hydrated due to reuse. We show that the native oxide film of Ti5553 powder is a hydroxylated mixed oxide composed of TiO2 and Al2O3 that grows from 5.6 +/- 0.7 nm to 8.3 +/- 1.1 nm due to reuse. Al oxide regions of the surface oxide become more hydroxylated during reuse in comparison to Ti oxide regions. This indicates that an outer oxide of pure TiO2 may enhance recyclability of Ti5553 powder while the presence of Al oxides may decrease recyclability. Further characterization of surface transformations due to recyclability may eliminate unnecessary variation in LPBF.

Oxidation behavior of AlCoCrFeNiSix high-entropy alloys at 1100 ℃

AlCoCrFeNiSix high-entropy alloys containing different Si contents (x = 0, 0.2, 0.5, 0.8, 1.0 in molar ratio) were prepared by vacuum arc-melting. The microstructure and oxidation behavior of these alloys at 1100℃ for 200 h were investigated. After adding Si, the alloys mainly consist of BCC and Si-rich precipitates, and both the size and quantity of the Si-rich precipitates increase with increase in the Si content. A suitable content of Si in the alloys improves the oxidation resistance for promoting the formation of a dense single Al2O3 scale, while excessive Si imposes an adverse effect by forming easy-peeling scales composed of Al2O3 outer layer and mixed oxides inner layer. Formation and failure mechanisms of the oxide scales on these alloys during oxidation have been discussed.

Corrosion behavior and mechanism of selective laser melted Ti35Nb alloy produced using pre-alloyed and mixed powder in Hank’s solution

This work investigated the corrosion behavior and mechanism of selective laser melted (SLM) Ti35Nb separately using mixed powder (Ti35Nb-M) and pre-alloyed powder (Ti35Nb-P) in Hank’s solution. Both types of samples demonstrate similar corrosion behavior, and double-layered oxide films form on the TiNb regions in both Ti35Nb-M and Ti35Nb-P. However, Ti35Nb-P has more stable oxide films than Ti35Nb-M because the outer porous oxide layer formed on Ti35Nb-P has smaller thickness and less defects according to Mott-Schottky analysis. Distinct oxide films also form on the TiNb and Nb regions in Ti35Nb-M due to unmelted Nb particles.

Selective oxidation of nanoscale nickel-based superalloys revealed by multi-dimensional electron tomography

Selective oxidation is one of the most important oxidation phenomena in multi-phase or multi-component alloys. Complex multi-layered oxides with randomly distributed pores beneath the outer oxide deeply and comprehensively hamper conventional studies. Multi-dimensional structures and elemental distributions are reconstructed on the initial oxidation of typical second- and third-generation Ni-based single crystal superalloys by electron tomography. The initial oxidation of the second-generation alloy has a two-layered structure with an outer Ni-rich oxide layer and an inner Al-rich oxide layer. The γ phase in the third-generation alloy is easily oxidized to form a rough surface with extruded oxide particles.

Effect of Y on high-temperature oxidation behavior and products of AZ80 alloy

Oxidation resistance and products of the AZ80 alloys with (0, 0.32, 1.07 wt %) Y were investigated via isothermal oxidation test at temperatures between 413 °C and 445 °C. The results revealed that alloys showed linear or power law kinetics weight gain with time at each temperature. The alloying element Y facilitated the reaction of MgO + CO2MgCO3 in the outer oxide layer of AZ80, which changed flocculent shape oxides (MgO) to granular oxides (MgCO3). Oxide layer with flocculent shape oxides is loose, while that with granular oxides is compact and can prevent alloy matrix from further oxidation. A further insight into oxidation mechanism of magnesium alloys is obtained.

Effects of pH and H2O2 on the chemical mechanical polishing of titanium alloys

Titanium alloys have been widely used in many high-end components and parts in various fields, and the excellent surface quality of titanium alloys is highly required. In this study, chemical mechanical polishing (CMP) was used as an effective surface processing technology, and the effects of pH and H 2 O 2 on the CMP performance of titanium alloys TA2 (pure titanium) and TC4 (Ti-6Al-4 V) were thoroughly investigated. It is shown experimentally that TA2 and TC4 perform the similar CMP performance as a function of either pH or H 2 O 2 . As pH increases from 4 to 10, the material removal rate (MRR) decreases while the surface roughness R a increases; At pH 4, as the H 2 O 2 concentration increases, the MRR first rapidly increases, reaches the summit at approximately 0.05 wt% H 2 O 2 , and then gradually decreases, while the R a first decreases and then slightly increases. An optimal polishing performance can be achieved at 0.05 wt% H 2 O 2 and pH 4. By characterizing the surface films of TA2, it is revealed that an oxide film with 3−4 nm thickness is formed after polishing, and the crystal structure of the underneath substrate remains complete without damage. The oxide film consists of two layers. The H 2 O 2 -dependent CMP performance can be attributed to the change of the outer oxide layer. Specifically, by adding 0.05 wt% H 2 O 2 , the oxide film can be rapidly formed, matching with the abrasion, and the outer oxide layer becomes compact, and thus the MRR increases and the R a decreases. The findings can provide a feasible CMP process for titanium alloys to achieve a satisfactory polishing performance.

Investigation on the mechanism of deteriorated oxidation resistance of Ti(C0.7,N0.3)-304ss cermet doped with Y during the early oxidation stage

The high-temperature oxidation resistance of the Ti(C0.7,N0.3)-304ss cermets during the early oxidation stage was deteriorated by adding Y. The outward diffusion of Fe atoms was improved with Y addition, and a Fe-rich outer oxide layer was generated on the surface. Impurities at phase boundary act as barriers to suppress the diffusion of Fe and O atoms; while they were purified by Y atoms, and the barriers were destroyed. As a result, the oxidation resistance deteriorated. The apparent activation energy of the cermets declined from 207.18 KJ/mol to 149.97 KJ/mol by doping with Y.

Oxygen injection during fast vs slow passivation in aqueous solution

The typical defect reactions at the metal/oxide interface, which explain the growth and breakdown of passive oxide films in corrosion, include creating metal and oxygen vacancies. While the creation and coalescence of metal vacancies are well documented, there are relatively few observations on the nanoscale details of oxygen transport near the metal/oxide interface. We report here a new mechanism of oxygen injection into the metal. Fast and slow passivation (i.e., corrosion involving both oxide film growth and direct dissolution) of NiCr and NiCrMo alloys was performed by galvanostat experiments in 0.1 M NaCl (pH 4) deaerated solution. Localized regions of an unexpected nonequilibrium metal-based oxygen solid solution were observed beneath the outer (externally formed) oxides, and the saturated oxygen atoms distorted the fcc metallic lattices. Oxygen injection into the metal is more significant at a fast growth rate due to a large passivation current density for the NiCr alloy. In this case, there is a high volume of rock salt Ni(Cr)O nanocrystals in the O-rich Ni(Cr) substrate, which is consistent with greater susceptibility to chloride-induced breakdown found in potentiostat experiments. The addition of Mo promotes the formation of the corundum phase in the outer oxide layer for NiCrMo, which changes the transport mechanism as well as the diffusivity of oxygen through the oxide film and across the metal/oxide interface.

Surface Modifications Induced by Pretreatments and Effects on The Chemical Structure of TCP Conversion Coating on Al-Cu-Li Alloy (AA2050)

Trivalent Chromium Process (TCP) was developed as a promising conversion process aiming at enhancement of corrosion properties and adhesion of aluminium alloys. The alkaline etching and acid pickling are usually applied as surface pretreatments on aluminium alloys before TCP deposition in order to optimize their properties. In this work, the surface modifications of an Al-Cu-Li alloy (AA2050-T8) at different stages of pretreatment (alkaline degreasing and acid pickling) and subsequent TCP are investigated by X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry and scanning electron microscopy. The pretreatments leading to significant enrichments in Cu and less marked in Ag, show also a strong influence on the subsequent formation of TCP in comparison to the non-pretreated, polished AA2050-T8 alloy. A slight decrease in Li content is observed in the oxide layer after pretreatment and no Li is present in the outer TCP layer. A thicker TCP conversion coating (outer oxide) with less cracks is formed on the pretreated alloy surface than on the polished one. Moreover, a Cu enrichment is evidenced in the TCP layer of the pretreated sample, which results in enhanced cathodic activity of pretreated sample with reference to polished sample as demonstrated by linear sweep voltammetry.

High temperature oxidation behavior and mechanism of FeXCr0.5Ti ferritic stainless steels

In order to investigate the oxidation mechanism of ferritic stainless steel during long-term oxidation at high temperature. The oxidation behavior of Fe-Cr-Ti ferritic stainless steels with 10.38 wt% Cr and 17.41 wt% Cr at 800 °C and 900 °C for 100 h was studied by a constant temperature weight gain method. The morphology and composition of the oxide film were characterized by SEM, EDS and XRD. The experimental results indicate that the oxygen element mainly diffuses inward at 800 °C for two stainless steels, and the oxide film is composed of (Cr1.3Fe0.7)O3 + MnCr2O4. When the temperature rises to 900 °C, metal element mainly diffuses outward, and Fe2O3 outer oxide layer and Fe rich Fe-Cr inner oxide layer are formed in Fe11Cr0.5Ti stainless steel; Cr2O3 + Cr rich M3O4 spinel oxide film is formed in Fe18Cr0.5Ti stainless steel, while the inner layer is composed of SiO2. The main reason for the significant decrease of oxidation resistance of Fe11Cr0.5Ti stainless steel is that the low content of Cr cannot form a Cr rich oxide layer to inhibit the outward diffusion of Fe element, and the stability of oxide film is poor to protect the matrix.

Influence of oxygen content on the corrosion behaviour of 316 L stainless steel in the simulated cathodic environment of proton exchange membrane fuel cell

316 L stainless steel (316 L SS) was melted in three different vacuum degree environments, and the oxygen content of the melted 316 L SS was measured using a routine method (ISO 15351:1999). The results revealed that oxygen content decreased with increasing vacuum degree during the melting process. Then, the influence of oxygen content on the corrosion behaviour of 316 L SS in the simulated cathodic environment of proton exchange membrane fuel cells (PEMFCs) was investigated using potentiodynamic curves, electrochemical impedance spectroscopy (EIS), Mott-Schottky plots, auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The results show that decreasing the oxygen content can significantly increase the passivity of 316 L SS in the simulated cathodic environment. EIS and Mott-Schottky plot results show that a passive film can be formed on 316 L SS in a simulated cathodic environment, and the compactness and resistance of the passive film increase with decreasing oxygen content, indicating improved corrosion protection of the passive film. Meanwhile, the passive film exhibits semiconductive characteristics, and the defect density decreases with decreasing oxygen content, implying increased homogeneity and stability of the passive film on 316 L SS. The AES and XPS results show that the passive film on 316 L SS consists of an inner Cr2O3 film and an outer iron oxide film, in which the thickness of the passive film and the content of the inner Cr2O3 film increase with decreasing oxygen content. Thus, it can be concluded that the corrosion protection of the passive film on 316 L SS increases with decreasing oxygen content considering the main corrosion protection contribution of the Cr2O3 film.