Thickness Of Oxide Layer Research Articles

3D printed N-doped CoCrFeNi high entropy alloy with more than doubled corrosion resistance in dilute sulphuric acid

The traditional approaches for improving corrosion resistance of alloys typically lead to the sacrifice of mechanical properties because the microstructures needed for improving corrosion resistance often contradict those for high strength. Here we demonstrate that selected laser melting (SLM), a net-shape additive manufacture technique, can maintain good mechanical properties while double the corrosion-resistance of a N-doped CoCrFeNi HEA. The SLM processed sample possesses a heterogeneous microstructure with 3D dislocation cells inside each grain. The SLM-induced 3D dislocation cell structure can provide effective diffusion paths to significantly promote Cr outward segregation, forming a thick protective Cr oxide layer, which renders excellent corrosion resistance. Furthermore, Cr segregation along cell boundaries provides numerous sites for nucleation of oxides, and stabilizes the cell structure for good mechanical properties. The strategy discovered here may also be applied to other HEAs with multiple strengthening mechanisms.

Oxidation Kinetics of Ti-6Al-4V Alloys by Conventional and Electron Beam Additive Manufacturing.

New manufacturing processes for metal parts such as additive manufacturing (AM) provide a technological development for the aeronautical and aerospace industries, since these AM processes are a means to reduce the weight of the parts, which generate cost savings. AM techniques such as Laser Powder Bed Fusions (LPBF) and Electron Beam Fusion (EBM), provided an improvement in mechanical properties, corrosion resistance, and thermal stability at temperatures below 400 °C, in comparison to conventional methods. This research aimed to study the oxidation kinetics of Ti-6Al-4V alloys by conventional and Electron Beam Additive Manufacturing. The thermogravimetric analysis was performed at temperatures of 600 °C, 800 °C, and 900 °C, having a heating rate of 25 °C/min and oxidation time of 24 h. The microstructural analysis was carried out by thermogravimetric analysis. Thickness and morphology of oxide layers were analyzed by field emission scanning electron microscope, phase identification (before and after the oxidation process) was realized by X-ray diffraction at room temperature and hardness measurements were made in cross section. Results indicated that the oxidation kinetics of Ti-6Al-4V alloys fabricated by EBM was similar to conventional processing and obeyed a parabolic or quasi-parabolic kinetics. The samples oxidized at 600 °C for 24 h presented the lowest hardness values (from 350 to 470 HV). At oxidation temperatures of 800 and 900 °C, however, highest hardness values (from 870 close to the alpha-case interface up to 300 HV in base metal) were found on the surface and gradually decreased towards the center of the base alloy. This may be explained by different microstructures presented in the manufacturing processes.

Oxidation-Affected Erosion of Porous Ni-Al Intermetallic Alloy in Combustion Applications: Pore-Scale Simulation

Advanced high-temperature oxidation resistance is a crucial characteristic of metallic materials in porous burners. Extreme combustion conditions could lead to oxidation-affected erosion of porous media at a long-time period of burner operation. In this paper, we numerically simulated oxide scale growth at a porous radiant burner fabricated by Ni-Al intermetallic alloy using the combustion synthesis method, focusing on the structure degradation caused by periodic oxide scale spallation. A three-dimensional geometrical model of a porous intermetallic scaffold was obtained by scanning the porous burner using the X-ray CT technique. The surface erosion was modeled by the surface reconstruction based on calculated values of spalled oxide layer thickness. The simulation revealed that the submerged flame results in non-uniform distribution of the temperature at the solid surface. Such non-isothermal conditions lead to a two-times thicker oxide scale at the external surface of the burner. Thin struts of the intermetallic scaffold are prone to oxidation-affected erosion first, which forms discontinues and further fragmentation. The porous scaffold could lose about 50% of initial weight before fragmentation under conditions with intense oxide spallation. In such large structural degradation, the average flow velocity could reduce by a factor of 3, leading to changing of flame stabilization region.

Understanding the Influence of Metal Oxide Layer Thickness and Defects on Resistive Switching Behavior Through Numerical Modeling

The resistive switching dynamics in metal–insulator–metal (MIM) structures may be explained through the formation and rupture of metallic filaments in the dielectric layer. Considerable research has been performed as an attempt to explain the microscopic origins of how regions that are originally insulating can change into conductors. Looking at how these conducting local regions are interconnected, the simulation of these localized switches can help understand how material properties such as thickness and defects influence the switching behavior and parameters. Here, the random circuit breaker (RCB) model is implemented and the dependence of the forming, Set, and Reset voltages on the oxide thickness and defect percentage is compared with experimental data. Only the forming voltage increases with the thickness, showing that, after the first step, the conductive filament formation and rupture occur only at a thinner thickness. It is observed that a higher percentage of initial conductive defects in the oxide layer promotes the forming step.

Simulation-Assisted Process Design and Experimental Verification of Laterally Confined Oxide Areas Generated with Continuous Electrolytic Free Jet on EN AW-7075 Aluminum Alloy

Local anodization with a free electrolyte jet is a suitable solution for locally confined surface functionalization without additionally required preparation of the parts. However, the geometrical formation of the anodic oxide layer in jet-based anodization is not yet sufficiently understood. In this study, numerical calculations based on physical descriptions are used to describe the lateral and vertical oxide formation on aluminum alloy EN AW-7075. The required electrical resistance and capacitance were determined by immersion-based anodization and implemented into the numerical simulation model to evaluate the electrical conductivity of the porous layer. The simulation results showed an electrical conductivity of 2.6 × 10-6 S/m for the porous layer. Subsequently, a model for jet-based anodization was developed and the previous results were implemented to calculate the oxide formation. The simulation results showed decreasing oxide layer thickness at increasing radial distance from the center of the jet, which corresponds to experimental results. The simulation model was validated by varying the current efficiency from 5% to 90%, where similar developments of the anodic oxide layer thickness compared with experimental results were determined at 5%.

Oxidation Behaviors of ZrB2–SiC Ceramics with Different Porosity

ZrB2–SiC ceramics have great application potential in thermal protection system of hypersonic aircraft, due to their excellent oxidation resistance and mechanical properties. Porosity is one of the main factors which will obviously affect the oxidation behaviors of ZrB2–SiC ceramics. Herein, ZrB2–SiC ceramics with three different porosity are sintered by spark plasma sintering at different temperatures. Then, a series of oxidation tests of the ceramics with different porosity are carried out at different temperatures and with different time. Morphologies and microstructures of the oxidation surface and cross section, as well as the oxide layer thickness and weight change are discussed in detail. Results show that the porosity of ZrB2–SiC ceramics has great influence on the oxidation behaviors of ceramics. The oxide layer thickness and weight change gradually increase with the increase of oxidation temperature and oxidation time for ZrB2–SiC ceramics with different porosity. As the porosity of ZrB2–SiC ceramics decreases, the oxide layer thickness and weight change generally decrease, which shows that the ceramics with lower porosity have stronger oxidation resistance. This work provides a relative systematic analysis of the effects of porosity on the oxidation behaviors of ZrB2–SiC ceramics.

Micro- and macro-scale characterization of the microstructure and scratch resistance of the 5083-anodic aluminum oxide film

This paper focuses on the thickness, microstructural, and scratch resistance of the sulfuric oxide layer of 5083-aluminum alloy for different anodizing durations/reaction times (RT = 30, 60, and 90 min). The thickness and the microstructure analyses were carried out using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, and ImageJ post-processing software. The scratch resistance was investigated using macro- and micro-scratch tests. Experimental results revealed that the oxide layer was covered by larger-sized microcavities and a thicker oxide layer for 90 min RT. Moreover, the area, which was covered by microcavities percentage, was decreased for 60 min RT and increased for 90 min RT. Besides, using the macro-scratch test, and when increasing RT, no micro-cracks were detected inside the scratch mark. Nerveless, the increasing of the normal load was shown that the oxide layer was more resistant to scratch. Finally, the 5083-aluminum alloy oxide layer had a high-scratch resistance such as a weak penetration depth and a low friction coefficient.

Degradation mechanism of near stoichiometric SiC fibers after air and Ar–H2O–O2corrosion at 1000–1500°C

AbstractThe near stoichiometric SiC fiber has been reported to play significant roles in the application of aeroengine field. An in‐depth understanding on the degradation mechanism of the fiber during its corrosion in air and under a simulated aeroengine environment (PH2O:PO2:PAr = 14:8:78 kPa) will shine a light on the performance evaluations of the near stoichiometric SiC fiber‐based materials as well as the development of their potential applications. In this study, X‐ray diffraction, scanning electron microscope, and FIB‐TEM were utilized to analyze the mechanical properties and microstructure of the fiber. After oxidation in dry air and Ar–H2O–O2for 1 h, respectively, the fiber strength retention rate has been found to decrease with the increased oxidation temperature. The raise in oxidation temperature also led to the increase of the thickness and the crystallization rate of the oxide scale. The most different oxidation behaviors of SiC being treated under the simulated environment than in air are the lower oxidation activation energy and the higher crystallization activation energy for cristobalite. Water vapor can promote the oxidation reaction and inhibit the crystallization of cristobalite in the oxide scale. Few significant differences have been observed otherwise in the oxidation process and oxidation chromatography crystallization mechanism of fibers being treated under different conditions. The increase of oxide layer thickness and the formation of cristobalite impair the structural integrity and compactness of the oxide scale and thus lead to the deterioration of the mechanical properties of SiC fibers. Therefore, it is proposed that oxidation resistance of SiC fiber can be improved by insulating the reaction between the oxidizing agents and the SiC fiber or by increasing the crystallization temperature of cristobalite in the oxidation process and reducing the crystallization rate.

Oxide thickness-dependent resistive switching characteristics of Cu/HfO2/Pt ECM devices

HfO2-based resistive random-access memory devices are promising candidates for new memory and computing applications. Hereby, scaling of the devices is a key issue, where overall fundamental switching and conduction mechanisms can be easily influenced by changes in the oxide layer thickness. This work addresses the oxide thickness-dependent resistive switching characteristics in Cu/HfO2/Pt memory devices through bipolar DC switching characterization. Forming, reset, and set characteristics are investigated depending on the oxide layer thickness, revealing a significant difference for thicker compared to thinner films. Thicker samples tend to show a more abrupt reset behavior and a larger set voltage variance, while for thinner samples, a more gradual reset behavior and a low set variance is found. These phenomena can be explained by a model based on thermally assisted electrochemical metallization. Furthermore, to understand the conduction mechanism of the devices, current–voltage curves of the set process were investigated. The devices are found to have an Ohmic conduction mechanism in the lower voltage region generally, while thinner samples tend to show an additional space-charge-limited current conduction mechanism in a higher voltage region.

Nanoscale characterization of the heterogeneous interfacial oxidation layer of graphene/Cu based on a SEM electron beam induced reduction effect.

Characterization of the interfacial oxidation layer of graphene/metal is a challenging task using conventional spectroscopy techniques because interfacial oxidation is heterogeneous at the nanoscale underneath the graphene. Here we developed a feasible method for nanoscale characterization of the interfacial oxidation layer of graphene/Cu (Gr/Cu) based on scanning electron microscopy (SEM) electron beam irradiation (EBI) induced reduction of interfacial oxides (SEM EBI-RIO method) at room temperature. The change in the thickness and coverage of the interfacial Cu oxide layer induced by EBI is responsible for the observed contrast reversal or change in SEM images of a targeted area with a width down to 200 nm in the EBI time scale of seconds to minutes. This method offers the capability of mapping heterogeneous interfacial oxidation of Gr/Cu with sub-100 nm spatial resolution and determining the range of thickness (1-5 nm) of the interfacial oxide layer. The SEM EBI-RIO method will be a powerful method to complement X-ray photoelectron spectroscopy (XPS), Raman microscopy, and high resolution transmission electron microscopy (HRTEM) for characterization of the interfacial oxidation layer of 2D materials and devices.

Effects of surface oxide layer on the impact dynamic behavior of molten aluminum droplets

Oxide layer is easily formed on the surface of some metal droplets, which affects the dynamic behavior of droplet impact. In this paper, experiments were conducted for the impacting process of a molten aluminum droplet on a Teflon substrate. The thickness of surface oxide layer of aluminum droplets was controlled by varying oxygen concentrations in the gas atmosphere. The effects of oxygen concentration and Weber number on droplet spread, rebound, and splash behavior were investigated. The results show that the oxygen concentration in the environment directly affects the droplet impact behavior. The differences in the droplet retraction process at different oxygen concentrations are more significant than the spread process. Strong retraction causes droplet rebound (We = 17.11) and splash (We = 102.3) in hypoxic environments, whereas only weak retraction in air. The viscous dissipation of the droplet impact in different oxygen concentration environment is estimated by counting the droplet bounce height, and the dissipation increases with the increase in the oxygen concentration. The thickness of the oxide layer measured by scanning electron microscope became thinner as the oxygen concentration decreases and, accordingly, the aluminum droplet collisions show different dynamic behavior. The experimental results are analyzed and explained regarding the reduction in surface tension, the increase in viscous forces, and the shear-thinning properties which increase the viscous dissipation during retraction. Ryan model was used to predict the droplet maximum spreading factor ξmax with the Weber number to the power of 0.5, better than the energy conservation-based Pasandideh-Fard model.

Effect of Rear Contact Coverage and Improvement of Efficiency of Crystalline p-Si Solar Cell Compared to State of Art PERC Cell

A device simulation model for localized contact rear side oxide-passivated solar cell was developed to study the effects of rear contact coverage and fixed charge density dependent field-effect passivation on the performance of a p-Si solar cell. Models describing hetero-interface physics related to metal-semiconductor, metal-oxide-semiconductor junctions and interface recombination are considered in the simulation, results of which are verified with the reported experimental data. A detailed analysis of the effect of surface passivation is presented and an analytical design with optimized set of parameters is outlined for fabricating the cell. The results show that the efficiency of the solar cell can be substantially enhanced by controlling parameters such as the ratio between localized back contact to the non-contact area and the fixed charge density at the oxide-interface. A maximum efficiency of ~ 24.5% for a crystalline p-Si solar cell with a comparatively lower lifetime can be obtained by a suitable choice of the design parameters with an added suitable choice of doping concentration in the emitter and absorber and the oxide layer thickness.

Simulation Study of Enhancement Mode β-Ga2O3 MOSFET with Ferroelectric Charge Storage Gate Stack Structure

In this work, an enhancement-mode (E-mode) β-Ga2O3 metal-oxide-semiconductor field-effect transistor (MOSFET) with the ferroelectric charge storage gate stack structure is numerically investigated. The device is simulated from the aspects of traps and material parameters, physical models, and voltage sources. And we found that the device is optimal in performance when the ferroelectric film thickness is 17 nm and the oxide layer thickness is 5 nm. The threshold voltage shifts from −0.2 V to 4.47 V after initialization, which makes the device transit from depletion-mode (D-mode) to E-mode. Moreover, the reliability of device is presented from the aspects of repeated scanning and temperature characteristics to estimate the sensitivity of threshold voltage.

Recycled Aluminium Alloys and their Models: Role and Behaviour of Alloying Elements during Alkaline Etching

Alkaline etching is a common pretreatment for aluminum surfaces. Etching behavior was compared between an alloy based on post-consumer scrap (PCS) and several model alloys of rolled AA3005 and extruded AA6060 with systematically varied amounts of Mn, Cu and Ni. Analysis of concentrations of alloy elements in the etching solution by inductively coupled plasma mass spectrometry (ICP-MS) shows that significant fractions of the investigated elements Cu, Fe, Mg, Mn, Ni, and Zn dissolve. Surface analysis of samples in different stages of the etching process show (i) an increase in oxide layer thickness with etching time, (ii) an enrichment of important alloy elements and impurities (Cr, Cu, Fe, Mg, Mn, Si) near the metal/oxide interface, and (iii) the deposition of Mg, Fe, Si-containing aluminum hydroxide on the surface. A comparison with open circuit potential measurements and time-resolved electrochemical polarization resistance measurements enables a detailed analysis of the etching mechanism. The aluminum dissolution rate during etching is limited by the transport of species through the oxide precursor layer, thus is potential-independent. Differences in etching rates between different alloy classes, evidenced by mass loss measurements, are related to differences in the cathodic or anodic reaction mechanisms (hydrogen evolution or metal dissolution) during etching.

Surface nanocrystallization enhances the biomedical performance of additively manufactured stainless steel.

Additive manufacturing enables the fabrication of patient-specific implants of complex geometries. Although selective laser melting (SLM) of 316L stainless steel (SS) is well established, post-processing is essential to preparing high-performance biomedical implants. The goal of this study was to investigate surface mechanical attrition treatment (SMAT) as a means to enhance the electrochemical, biomechanical, and biological performances of 316L SS fabricated by SLM in devices for the repair of bone tissues. The SMAT conditions were optimized to induce surface nanocrystallization on the additively manufactured samples. SMAT resulted in a thicker oxide layer, which provided corrosion resistance by forming a passive layer. The fretting wear results showed that the rate of wear decreased after SMAT owing to the formation of a harder nanostructured layer. Surface modification of the alloy by SMAT enhanced its ability to support the attachment and proliferation of pre-osteoblasts in vitro. The study of the response in vivo to the additively manufactured alloy in a critical-sized cranial defect murine model revealed enhanced interactions with the cellular components after the alloy was subjected to SMAT without inducing any adverse immune response. Taken together, the results of this work establish SMAT of additively manufactured metallic implants as an effective strategy for engineering next-generation, high-performance medical devices for orthopedics and craniomaxillofacial applications.

THE INFLUENCE OF FRACTAL DIMENSION OF OXIDE LAYER ON PASSIVE OXIDATION OF THE C/SiC COMPOSITE

The C/SiC composite is a promising material for ablation-resistant thermal protection in near-space hypersonic environments. The formation of an SiO2 oxide layer through passive oxidation on the surface of the composite is a significant factor influencing its performance. It is essential to accurately predict the thickness of the SiO2 oxide layer and the recession and mass loss of the C/SiC composite during passive oxidation. The SiO2 oxide layer is a typical porous media exhibiting self-similarity and thus fractal theory can be applied to establish the relation between the oxygen flow rate and microstructural parameters of the oxide layer. The Weierstrass–Mandelbrot (WM) function is employed to simulate the rough interfaces between the SiO2 oxide layer and the C/SiC composite to evaluate the influence of the fractal dimensions of the oxide layer on the performance of thermal protection of the C/SiC composite. The results show that the C/SiC composite exhibits improved thermal protection performance when accompanied by a lower tortuosity fractal dimension and a higher pore area fractal dimension of the oxide layer. Conversely, the composite demonstrates enhanced ablation resistance with a higher tortuosity fractal dimension and a lower pore area fractal dimension of the oxide layer. The predictions of the calculation model show good agreement with the experimental data and demonstrate the critical influence of microstructural parameters of the oxide layer on passive oxidation of the composite, providing practical implications for designing materials with desired thermal protection or ablation resistance properties.

Влияние добавки наночастиц ZrO2 в электролит на структуру и антикоррозионные свойства оксидных слоев, формируемых плазменно-электролитическим оксидированием на сплаве Mg97Y2Zn1

Magnesium alloys with a strengthening long-period stacking ordered structure (LPSO-phase) offer outstanding mechanical properties, but their low corrosion resistance necessitates additional surface protection. The work investigates the influence of adding ZrO2 nanoparticles at a concentration of 1–4 g/l to the electrolyte on the thickness, structure, composition, wettability, and anticorrosion properties of oxide layers formed during plasma electrolytic oxidation (PEO) of the Mg97Y2Zn1 alloy with the LPSO-phase. It was found that during PEO, under the influence of an electric field, ZrO2 nanoparticles penetrate into the forming oxide layer and reduce its porosity. The study revealed a decrease in the quantity and size of pores near the barrier layer in places where the alloy LPSO-phase comes out to the interface with the oxide layer. Low concentrations of ZrO2 nanoparticles (1–2 g/l) reduce the corrosion rate of the alloy up to two times compared to the base case. The minimum corrosion current density icorr≈14 nA/cm2 and the highest polarization resistance Rp≈2.6 MΩ·cm2 are found in the sample formed in an electrolyte with the addition of 1 g/l of ZrO2 nanoparticles. Calculation of the barrier zone parameters of oxide layers showed that an increase in the ZrO2 concentration in the electrolyte leads to an increase in the barrier layer thickness and in its specific conductivity, which negatively affects the corrosion resistance of the formed oxide layers – the barrier zone resistance of the layer obtained by adding 4 g/l of ZrO2, drops by ~20 % compared to the base case (up to ~1 MΩ·cm2).

Influence of Silicon Oxide Layer Thickness on Electronic State Structure and Optical Properties of Si/SiO2 Interface

Influence of Silicon Oxide Layer Thickness on Electronic State Structure and Optical Properties of Si/SiO2 Interface

Long‐term oxidation and ablation behavior of Cf/ZrB2–SiC composites at 1500, 2000, and 2200°C

AbstractAlthough Cf/ZrB2–SiC composites prepared via direct ink writing combined with low‐temperature hot‐pressing were shown to exhibit high relative density, high preparation efficiency, and excellent flexural strength and fracture toughness in our previous work, their oxidation and ablation resistance at high and ultrahigh temperatures had not been investigated. In this work, the oxidation and ablation resistance of Cf/ZrB2–SiC composites were evaluated via static oxidation at high temperature (1500°C) and oxyacetylene ablation at ultrahigh temperatures (2080 and 2270°C), respectively. The thickness of the oxide layer of the Cf/ZrB2–SiC composites is <40 μm after oxidizing at 1500°C for 1 h. The Cf/ZrB2–SiC composites exhibit non‐ablative properties after oxyacetylene ablation at 2080 and 2270°C for >600 s, with mass ablation rates of 3.77 × 10−3 and 5.53 × 10−3 mg/(cm2 s), and linear ablation rates of −4.5 × 10−4 and −5.8 × 10−4 mm/s, respectively. Upon an increase in the ablation temperature from 2080 to 2270°C, the thickness of the total oxide layer increases from 360 to 570 μm, and the carbon fibers remain intact in the unaffected region. Moreover, the oxidation and ablation process of Cf/ZrB2–SiC at various temperatures was analyzed and discussed.

Impact of surface oxide on hydrogen permeability of chromium membranes

Hydrogen permeation through pure and oxidised bulk chromium membranes was measured by the classical gas technique to get insight into oxide as a hydrogen permeation barrier (HPB). An additional palladium-coated reference chromium membrane was tested to avoid the influence of native Cr oxide. Key parameters for Cr permeability: P0 = 3.23 × 10−7 mol H2/s/m/Pa0.5 and Ea = 0.68 eV and Cr diffusivity D0 = 9.0 × 10−5 m2/s and Ea = 0.59 eV. In the sample preparation stage, a thin ∼2 nm thick oxide was formed. Additional oxidation in pure oxygen at 400 °C increased the thickness from 20 to 50 nm. At this temperature, its efficiency as HPB was evaluated by comparing permeation rates to the reference chromium membrane. The highest permeation reduction factor of ∼3900 corresponded to only a ∼28 nm thick Cr oxide layer. Surface morphology and oxide thickness were investigated by SEM, while the thickness and type of chromium oxide by XPS.