Oxidation Of Alloys Research Articles

Effect of laser-assisted irradiation on plasma electrolytic oxidation of titanium alloys: Arc spot evolution characteristics and photoelectric synergistic mechanisms

Laser irradiation can be employed as an auxiliary energy field to optimize functional plasma electrolytic oxidation (PEO) coatings. Herein, the mechanism of the effect of laser-assisted irradiation on the morphology and composition of ceramic coatings prepared by PEO of titanium alloys in electrolytes with sodium tetraborate-based is discussed from the perspective of plasma arc spot evolution and photoelectric synergistic effect. X-ray diffraction (XRD), transmission electron microscopy (TEM), Mott-Schottky (M-S), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to analyze the coating characteristics. The results showed that laser-assisted irradiation promoted the oxidation of the coatings, accelerated the conversion of the anatase phase to the rutile phase, reduced the oxygen vacancy defects and formed the "ant nest" porous microstructure. Monitoring of the voltage, electric field, and plasma discharge arc spot indicated that laser-assisted irradiation restricted the electric field diffusion on the anode surface, reduced the termination voltage, and significantly increased the intensity (maximum discharge percentage increased from 14.238 % to 20.358 %) and uniformity of distribution of the plasma discharge. Instantaneous photoresponse curves and electrochemical impedance spectroscopy confirmed that the PEO coatings exhibited fast and sustained photoelectric response under simultaneous laser irradiation, progressively enhanced with increasing laser irradiation energy. The photogenerated electrons excited by the semiconductor TiO2 coating under the simultaneous irradiation of laser can be used as the initial carriers of the electron avalanche, which induces the generation of a plasma on the surface of the anode and thus enhances the plasma discharge behavior, which is the fundamental reason for the optimization of the coating characteristics.

Atomic-Scale Dynamics of the Initial Stages of Cu and Cu Alloy Oxidation

Atomic-Scale Dynamics of the Initial Stages of Cu and Cu Alloy Oxidation

Research Progress on the Oxidation Behavior of Ignition-Proof Magnesium Alloy and Its Effect on Flame Retardancy with Multi-Element Rare Earth Additions: A Review.

The phenomenon of high-temperature oxidation in magnesium alloys constitutes a significant obstacle to their application in the aerospace field. However, the incorporation of active elements such as alloys and rare earth elements into magnesium alloys alters the organization and properties of the oxide film, resulting in an enhancement of their antioxidation capabilities. This paper comprehensively reviews the impact of alloying elements, solubility, intermetallic compounds (second phase), and multiple rare earth elements on the antioxidation and flame-retardant effects of magnesium alloys. The research progress of flame-retardant magnesium alloys containing multiple rare earth elements is summarized from two aspects: the oxide film and the matrix structure. Additionally, the existing flame-retardancy models for magnesium alloys and the flame-retardant mechanisms of various flame-retardant elements are discussed. The results indicate that the oxidation of rare earth magnesium alloys is a complex process determined by internal properties such as the structure and properties of the oxide film, the type and amount of rare earth elements added, the proportion of multiple rare earth elements, synergistic element effects, as well as external properties like heat treatment, oxygen concentration, and partial pressure. Finally, some issues in the development of multi-rare earth magnesium alloys are raised and the potential directions for the future development of rare earth flame-retardant magnesium alloys are discussed. This paper aims to promote an understanding of the oxidation behavior of flame-retardant magnesium alloys and provide references for the development of rare earth flame-retardant magnesium alloys with excellent comprehensive performance.

Artificial intelligence approach to predict ladle aluminium content and to protect its refractory lining

ABSTRACT This research focuses on optimising steelmaking processes, specifically in the Basic Oxygen Furnace (BOF) and ladle operations, with an emphasis on ladle basicity and Aluminium dosage for deoxidation. The steelmaking process, conducted in the Basic Oxygen Furnace, involves oxidation, flux addition, and tapping of purified steel into ladles. Maintaining desired ladle basicity is crucial for high-quality steel production, and deoxidation with Aluminium is essential to prevent Ferro Alloy oxidation. Secondary metallurgy is performed to maintain ladle basicity and Aluminium content in the steel. The study introduces Artificial Intelligence (AI) integration, utilising Random Forest Regression model to predict Aluminium consumption. This AI-based approach enhances ladle basicity optimisation, reduces Aluminium usage, and ensures high-quality steel production. The research explores infrared technology, digital image processing, and colour visualisation for slag prevention during ladle tapping. The development of a Random Forest Regressor model surpasses empirical equations in predicting Aluminium consumption, resulting in superior ladle basicity maintenance. Comparative analysis demonstrates the accuracy of AI-aided ladles, optimising Al2O3 inclusion formation and sustaining ladle basicity. The research concludes by highlighting AI’s benefits, including improved steel quality, reduced secondary metallurgy, and enhanced operational efficiency, positioning AI as a valuable tool for cost-effective, energy-efficient, and reliable high-quality steel production.

Numerical modeling and experiment for isothermal selective external oxidation behavior of Fe-Mn binary alloys

This paper described work undertaken to the selective external oxidation of Fe-Mn binary alloys during isothermal recrystallization annealing. The effect of different peak temperature, soaking time, dew point conditions on external oxidation of Fe-Mn alloys were investigated. Based on an image segmentation technology, external oxidation behavior was evaluated by the equivalent diameters and coverage fraction of external oxides. A numerical kinetics model of the coupled selective internal-external oxidation during isothermal annealing of Fe-Mn binary alloys was proposed. The model allowed the case of internal and external oxidation simultaneously occurred. Based on the assumptions of oxidation reaction at the steel/atmosphere interface reached an instantaneously local thermodynamic equilibrium, the coupled relationship was described by two interactions. The surface dissolved oxygen content could be controlled by both the annealing atmosphere and the coverage fraction of external oxides on the surface, while the diffusion of oxidant and oxygen inside the steel were blocked by the precipitation behavior of internal oxides. Therefore, the model achieved predict quantitatively the coverage of oxides on the external surface of the steel and the mass fraction profiles of Mn after annealing. The correctness of the calculation results was verified experimentally.

INFLUENCE OF WELDING PARAMETERS ON THE PERFORMANCE CHARACTERISTICS OF THE THERMOCATODES

Methods of controlling welding parameters, physical and physico-chemical transformations that occur during welding are considered in the work. The physico-chemical mechanism of welding is considered - the deformation of the crystal lattice, the transfer of metal on the contacting surfaces, the mixing of deformation products, diffusion, phase transformations, the appearance of new chemical compounds - intermetallics, oxides, carbides. Studies of the influence of the main parameters of friction welding on the formation of the structure of the welded joints of the investigated alloys have been carried out. The microstructures of welded joints OT4 + VN-2AE and VT6 + VN-2AE are given. The obtained dependence of the relative strength of the OT 4 + VN-2AE connection on the parameters of the welding process. The given microstructures were obtained by SEM from the surface of OT 4 + VN-2AE and VT6 samples, based on which it was determined that the destruction begins with the formation of microcracks in the contact zone on the side of the VN-2AE niobium alloy. It was determined that a layer saturated with oxygen is formed in the diffusion zone due to which the β-modification of Ni2O5 with a significant specific volume is formed, which causes high internal stresses and the formation of microcracks. The reason for the decrease in the mechanical properties of the welded joint OT 4 + ВН-2АЕ was established - the formation of a phase (Ti-Nb) with an orthorhombic lattice, the degree of curvature of which determines the degree of strengthening of the layer and depends on the niobium content. These data are confirmed by X-ray structural analysis. The analysis of the concentration curves of niobium and titanium shows that titanium does not diffuse into the narrow contact zone of the niobium alloy, and niobium forms a wide diffusion zone in the contact zone of the OT 4 alloy. It was established that niobium contributes to the increase in the solubility of aluminum in λ-titanium, which leads to increase in weldability plasticity and corrosion resistance. It was determined that the low mechanical properties of the welded joints of the VN-2AE alloy with the OT-4 and VT-6 titanium alloys are due to the same nature - the oxidation of the niobium alloy at the welding temperature. It was established that the weak link of the welded joint is the surface of the niobium alloy.

Unveiling the diffusion pathways under high-temperature oxidation of Cr2AlC MAX phase via nanoscale analysis

The MAX phase chromium aluminium carbide (Cr2AlC) is a potential candidate for high-temperature structural and energy applications due to the unique combination of properties, including excellent oxidation and corrosion resistance in harsh environmental conditions. In this work, the oxidation behaviour of bulk Cr2AlC was studied at temperatures of 1000 °C and 1200 °C in humid synthetic air, mimicking a realistic application environment. An α-Al2O3 scale forms at both temperatures, consisting of both inward and outward-growing layers, with a continuous Cr7C3 layer beneath the oxide. A special focus was put on employing atom probe tomography (APT) to analyse the oxide and carbide layers at the nanoscale. Decomposition of Cr2AlC to Cr7C3 is the main source (>70%) of aluminium needed for the oxide scale formation, while Al depletion in the underlying MAX phase remains marginal (<1 at%), exhibiting a pattern different from the common high-temperature oxidation of alloys. Al diffusion to the oxide scale proceeds predominantly through grain boundaries (GBs) in Cr2AlC and through the bulk in Cr7C3. Ionic diffusion through GBs of the large-grained inner alumina layer seems to be the rate-limiting step for the oxide scale growth, resulting in the apparent parabolic oxidation kinetics. No segregation of Cr, C or any impurities, which could affect ionic transport, was found at these alumina GBs by APT, rendering the results of this study as characteristic of a pure Cr2AlC oxidation.

СТРУКТУРА И ПЕРСПЕКТИВЫ ПРИМЕНЕНИЯ В КАЧЕСТВЕ АДСОРБЕНТА ПОРИСТОГО ОКСИДИРОВАННОГО АЛЮМИНИЯ

The paper presents the results of microarc oxidation of porous aluminum made of alloys AlSi15, Д16 (D16) and AlMg6. According to research, on the surface of the sample, a composite oxide-ceramic coating is formed, consisting of mullite 3Al2O3‧2SiO2 and (or) various forms of aluminum oxide (α-, γ-Al2O3). It is shown that on the surface of porous aluminum, as well as in the pores of a cast sample, a coating is formed consisting of electropositive and electronegative sorption materials, aluminum oxides and aluminosilicates. Moreover, by changing the composition of the aluminum alloy and micro-arc oxidation modes, it is possible to control the phase composition of the coating being formed, which opens up the possibility of creating selective filter devices to retain either anionic or cationic inorganic compounds and microbiological objects.

Crystallinity regulation of ZIF-67 via defective MgO layer made by high voltage-assisted oxidation approach for optimal 4-nitrophenol reduction

Due to their unique structural characteristics, metal-organic frameworks (MOFs) have emerged as favorable contenders for photocatalytic applications. In this study, the crystallization of ZIF-67, a subclass of MOFs, on Mg and MgO substrates via dip coating was explored, and the resulting materials were employed as a photocatalyst for the 4-nitrophenol reduction. Due to the defective surface resulting from plasma activity during the high-voltage-assisted oxidation of AZ31 Mg alloy, MgO significantly impacts the crystallization of ZIF-67. This influence promotes the formation of a stable foundation and strong bonds, contributing to the emergence of a regular and symmetrical structure. This differs from the asymmetrical and irregular structure observed in ZIF-67@Mg when ZIF-67 is grown directly on the Mg substrate. Hence, the ZIF-67@MgO catalyst demonstrated remarkable enhancements in the reduction of 4-nitrophenol to 4-aminophenol, achieving an efficiency of approximately 97.12 % within 12 min under visible light. Importantly, the catalyst exhibited no stability decay even after ten consecutive cycles, surpassing the performance of previously reported catalysts. This research sheds light on the superior capabilities of ZIF-67@MgO in the context of visible-light-driven reduction of 4-NP. The results suggest potential for future progress in creating effective and eco-friendly photocatalytic materials for addressing environmental challenges.

Achieving excellent oxidation resistance in a Mg alloy by grain boundary adhesion and in-situ phase transformation

The oxidation resistance of Mg–Zn–Zr (ZK60) alloys with the addition of minor rare-earth element (RE) oxides (CeO2, La2O3) was investigated in 420 °C in air and pure O2 environments. It was revealed that the oxidation behavior of ZK60, ZK60-La2O3 and ZK60-CeO2 is different. In comparison to typical intergranular oxidation in ZK60 alloy, owing to diverse phase transformations between La and Mg, the La–Mg phase is continuously distributed in the grain boundaries, and furthermore, a dense and protective layer consisting La–Mg intermetallic phase is coated on the surface, which can effectively inhibit the oxidation of the Mg substrate, exhibiting excellent oxidation resistance. However, the presence of discontinuously distributed Ce-rich phases at the grain boundaries and the chain reaction during high-temperature exposure are the reasons for the deterioration of the oxidation resistance in ZK60-CeO2. It is anticipated that our findings will inspire the development of next-generation low-cost and excellent high-temperature performance Mg alloys.

The effect of plasma electrolytic oxidation of aluminum alloys on the structure and properties of protective oxide-ceramic coatings

The results of the studies of electrical modes of the high-frequency high-voltage plasma electrolytic oxidation (PEO) on the properties of the formed protective coatings on the B95 T1 and D16ч T aluminum alloys are presented. The control of the PEO process was carried out by changing the amplitude values of anode and cathode voltage pulses. The local mechanical characteristics and the structure of the PEO coatings were studied using instrumentedindentation and scanning electron microscopy. As a result of the studies, optimal modes of the PEO process were determined: potentiodynamic modes with a smooth decrease in the amplitude of anode voltage pulses at a speed of 5 V/min and a smooth increase in the amplitude of cathode voltage pulses at a speed of 1 V/min. The coatings formed in the optimal modes of the PEO were characterized by a reduced number of defects (microcracks, craters, pores) and high values of hardness of 27.5–27.8 GPa and elastic modulus of 286–309 GPa averaged over their thickness. These characteristics turned out to be higher by 33–45% and 15–30%, respectively, compared with a hardness and elastic modulus of the coatings, formed in other studied PEO modes.

Selective laser melting of Hastelloy-X alloy and cerium oxide reinforced Hastelloy-X composite: Microstructural examination and corrosion behavior

The study investigated the microstructures and corrosion behaviors of Hastelloy X (HX) and HX reinforced by cerium oxide particles (HX-C) produced by selective laser melting (SLM) and compared to the wrought equivalent (HX-W). The aim was to eliminate hot cracking and investigate the HX's corrosion behavior in the presence of cerium oxide particles. The HX samples showed fine cellular and columnar solidification structures with uniform-size sub-cells and severe microcracking. Incorporating cerium oxide particles (1 wt%) resulted in finer and relatively equiaxed grains without microcracking. The HX-W alloy contained a micron-sized carbide (Mo-rich M6C type) within the matrix. The HX-C sample displayed higher porosities compared to the HX sample (1.8 % against 0.3 %). Potentiodynamic polarization and electrochemical impedance spectroscopy tests were conducted in a standard NaCl solution at temperatures of 25, 50, and 70 °C to assess the corrosion behavior of Hastelloy samples. The HX-C matrix showed superior corrosion resistance compared to the HX-W and HX samples due to its finer grain structure and stable passive layer formation. Cerium oxide particles were found to be efficient in decreasing hot cracking and improving corrosion resistance.

Cast Alumina-Forming Austenitic Stainless Steels for High Temperature Heat Treatment Furnace Rolls

Abstract Alloy developers worldwide have struggled to create creep-resistant alumina-forming, iron-based austenitic stainless steels for use as high-temperature structural alloys, but with limited success in balancing alloy cost, oxidation, and creep resistance. This article describes the research and development of a novel cast alumina-forming austenitic stainless steel. This work won the prestigious Engineering Materials Achievement Award presented at IMAT 2023 in Detroit.

Evolution of microstructure and mechanical properties of aluminum matrix composites reinforced with dual-phase heterostructures

The trade-off between strength and plasticity has long been challenging in particle-reinforced aluminum matrix composites (PRAMCs). This study proposes an innovative approach for preparing aluminum matrix composites (AMCs) using a dual-phase hybrid of FeCoNiCrMn high entropy alloy (HEA) and multiscale aluminum oxide (Al2O3) particles. The microstructure evolution and strengthening mechanisms were evaluated through scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The results demonstrated that the dual-phase particle strengthening resulted from the alternating distribution and synergistic action of HEA and Al2O3 particles within the matrix, forming a continuous strain buffer with a strength gradient. Notably, introducing HEA and nano-Al2O3 led to a higher density of dislocations. Additionally, EBSD analysis revealed a uniform strain distribution within the AMCs, with a significant concentration of kernel average misorientation (KAM) near the grain boundaries (GBs). In terms of micromechanical properties, the micro-zones of heterogeneous phases exhibit exceptionally high elastic modulus and nanohardness. In terms of macroscopic mechanical properties, the material exhibited impressive ultimate compressive strength and compression ratio values of 447.9 MPa and 37.9 %, respectively. These results represented a remarkable enhancement of 72.1 % and 6.6 % compared to the single FeCoNiCrMn HEA strengthening. Moreover, when applying the HEA + nano-Al2O3 blending mode, the ultimate compressive strength further increased to 506.7 MPa, representing an astonishing boost of 94.7 %. This significant strength improvement can be attributed to effective interfacial bonding, grain refinement, and a high dislocation density resulting from both HEA and Al2O3 particles.

Wet oxidation of TiZrHfNbTaV high-entropy alloys: Role of grain-boundary and interdendritic diffusion

Refractory high-entropy alloys (RHEAs) are sensitive to thermal oxidation, significantly restricting their service performance and potential applications. However, the wet oxidation behavior of RHEAs has remained poorly understood despite the potential risk of catastrophic oxidation caused by water vapor. In this study, the oxidation mechanism of an equiatomic TiZrHfNbTaV high-entropy alloy (HEA) has been investigated in a wet atmosphere at elevated temperatures. Synchronous oxidation of all elements occurs at temperatures below 800 °C. At temperatures above 800 °C, preferential oxidation of Nb, Ti, and Zr, and internal oxidation of V occur on HEAs, which are thermodynamically less preferred as compared with oxidations of more reactive Hf and Ta. Experimental and theoretical analyses show that the oxide grain boundaries and substrate interdendritic regions of HEAs act as diffusion pathways for V and oxidizing species during preferential and internal oxidation processes. This work provides a fundamental understanding of the oxidation of multicomponent alloys in wet environments, which is helpful in the development of effective oxidation resistance strategies and innovative surface engineering techniques.

Development and investigation of a porous metal-ceramic substrate for solid oxide fuel cells

The process of creating a porous metal-ceramic material based on Ni-Al alloy and gadolinium-doped cerium oxide (CGO) using the thermal explosion method has been investigated. This study aims to analyze the effect of CGO on the thermal explosion parameters and the architecture of the resulting Ni-Al-CGO materials. In this regard, the influence of adding CGO powder to the Ni-Al system on the synthesis process and structure formation during controlled heat loss thermal explosion has been studied. Dependencies of temperature and time characteristics of the thermal explosion on initial parameters have been measured. It has been demonstrated that the concentration of CGO in the initial mixture and heat dissipation from the sample significantly affect the rate of the exothermic reaction. The phase composition of the obtained porous materials, depending on the CGO content and the temperature of subsequent vacuum annealing, was analyzed using X-ray diffraction. The chemical composition and microstructure of the synthesis products were examined through electron microscopy and energy-dispersive X-ray spectroscopy. The possibility of forming metal-ceramic composites with a porosity of 60–65 % for use as supporting substrates for solid oxide fuel cells with a NiO/CGO anode has been shown. An anodic layer of NiO/CGO was applied to a metal-ceramic base of the composition (Ni+25 %Al)+5 %CGO using screen printing, which was then annealed in an air atmosphere at 1300 °C and reduced at 900 °C in a hydrogen atmosphere. The dilatometric method determined that adding 40 wt.% Cr to a mixture of Ni-Al powders reduces the average coefficient of thermal expansion of the new material.

The effect of Sn microalloying on the selective oxidation of Fe-(6-10 at.%)Mn alloys

To evaluate the suitability of Sn microalloying as strategy to decrease the selective oxidation kinetics of Mn-alloyed advanced steels, the effects of 0.01 and 0.03 at.% Sn micro-additions on oxide morphology and oxidation kinetics for Fe-6Mn and Fe-10Mn (at.%) alloys were determined under annealing conditions characteristic of the continuous galvanizing process. Selective oxidation followed a parabolic rate law, where activation energy analysis revealed that internal oxidation is rate-determined by the grain boundary diffusion of O in Fe. The 0.01 and 0.03 at.% Sn additions significantly reduced the internal oxidation of alloys with Mn contents of 6 and 10 at.%, which was attributed to interfacial Sn segregation reducing the solubility of O in Fe, the occupation of adsorption sites for water vapour molecules, and the reduction of short-circuit diffusion of O along internal interfaces. Sn microalloying decreased the external oxidation of Fe-6Mn-(0.01,0.03)Sn, but did not significantly alter external oxide thickness of the Fe-10Mn-(0.01,0.03)Sn alloys. In this case, Sn reduced the outward diffusion of Mn along grain boundaries, but also affected the balance between the inward O flux and outward Mn flux. Incorporating the effect of Sn occupying adsorption sites into a selective oxidation model revealed that Sn microalloying is predicted to cause a transition from internal to external oxidation for Fe-10Mn. For Fe-6Mn alloys, however, a Sn micro-addition of 0.01 at.% (∼0.022 wt.%) was sufficient to significantly reduce selective oxidation kinetics and produce beneficial alterations to the external oxide morphology in order to ease reactive wetting in the continuous galvanizing process.

Alloying effects of Al, Si and Fe on Ni-20Cr alloy oxidation in water vapour at 650 °C

Ni-20Cr alloys with or without minor elements (Al, Si, Fe) were oxidized in Ar-5 H2O at 650°C. The undoped alloy formed a feathery NiO external scale and a thick internal oxidation zone (IOZ). Additions of Al, Si and Fe improved oxidation resistance by changing oxide morphologies and reducing the IOZ. For Al and Si additions, more surface area formed a chromia scale with Al2O3 or SiO2 precipitates underneath. In addition, needle-shaped precipitates with a lamellar structure of chromia mixed with alumina or silica were observed. For Fe addition, a multi-layered oxide scale was formed with additional Fe-rich spinel, improving oxidation resistance.

Exploring the Influence of Nanocrystalline Structure and Aluminum Content on High-Temperature Oxidation Behavior of Fe-Cr-Al Alloys.

The present study examines the high-temperature (500-800 °C) oxidation behavior of Fe-10Cr-(3,5) Al alloys and studies the effect of nanocrystalline structure and Al content on their resistance to oxidation. The nanocrystalline (NC) alloy powder was synthesized via planetary ball milling. The prepared NC alloy powder was consolidated using spark plasma sintering to form NC alloys. Subsequently, an annealing of the NC alloys was performed to transform them into microcrystalline (MC) alloys. It was observed that the NC alloys exhibit superior resistance to oxidation compared to their MC counterparts at high temperatures. The superior resistance to oxidation of the NC alloys is attributed to their considerably finer grain size, which enhances the diffusion of those elements to the metal-oxide interface that forms the protective oxide layer. Conversely, the coarser grain size in MC alloys limits the diffusion of the oxide-forming components. Furthermore, the Fe-10Cr-5Al alloy showed greater resistance to oxidation than the Fe-10Cr-3Al alloy.

A computational note on thermal attributes of engine oil with titanium alloy and zinc oxide hybrid nanoparticles flowing over a stretching surface about a stagnation point

A computational note on thermal attributes of engine oil with titanium alloy and zinc oxide hybrid nanoparticles flowing over a stretching surface about a stagnation point