Surface Composition Of Alloys Research Articles

Microstructure and mechanical properties of Al2O3/AZ61 Mg alloy surface composite developed using friction stir processing and groove reinforcement filling processes

Abstract In this work, the alumina (Al2O3) particles-reinforced AZ61 magnesium (Mg) alloy surface composite was fabricated using friction stir processing (FSP) and groove reinforcement filling methods. The Mg alloy surface composites were developed with and without the addition of Al2O3 reinforcing particles, and their mechanical performance was compared with each other and with unprocessed base metal (BM). The Al2O3 powder was compressed into a groove of 4.5 mm depth that had been created in AZ61 Mg alloy plates. The volume fraction of Al2O3 powder was increased to 5, 10, and 15 vol.% depending on the width of the groove. Results disclosed that the problem of cluster formation of reinforcing Al2O3 particles was minimized by performing FSP in five number of passes. The ultimate tensile strength (UTS) and hardness of AZ61 Mg alloy were enhanced by 6.07 % and 22.23 % when it was subjected to FSP. This is primarily correlated to the significant refining of grains due to the severe plastic deformation associated with FSP. The 15 vol.%-FSPed Al2O3/AZ61 Mg alloy surface composite showed a higher UTS of 630 MPa and hardness of 300 HV. This is due to the integration of a greater quantity of Al2O3 particles with substantial grain refining.

Corrosion behavior analysis and characterization of AA7178 matrix alloy reinforced with nano TiO2 particles

The objective of this study is to assess how AA7178 matrix-based nanocomposites’ microstructure and corrosion properties are affected by the addition of nano TiO2 particles. The AA7178 alloy reinforced TiO2 composites were manufactured via stir-casting, with the TiO2 reinforcement levels ranging from 0% to 3% by 1% increments. A uniform distribution of TiO2 nanoparticles(2 wt%) over the Al matrix was shown by scanning electron microscopy analysis. The electrochemical behaviour of the base alloy matrix and surface composites was thoroughly investigated in a solution containing 3.5% sodium chloride utilizing open-circuit potential (OCP), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). Research using polarization and EIS showed that the nanocomposites were more resistant to corrosion than the matrix alloy. Subsequent examination indicated that the increased resistance to corrosion observed in the composites containing TiO2 particles might be a result of electrochemical decoupling between the AA7178 matrix alloy and the TiO2 particles. In order to stop the corrosion from spreading, this decoupling action is vital since it protects the TiO2 particles from the matrix alloy. The composite material AA7178/2 wt% TiO2 showed the best corrosion resistance, with ideal values for potential corrosion (−0.20622 V) and current density corrosion (0.00344 mA cm−2). The main causes of corrosion were shown to be pitting and cracking by scanning electron microscopy (SEM) study, highlighting the usefulness of TiO2 in reducing these negative impacts. This work illuminates the corrosion behaviour of AA7178/TiO2 nanocomposites and emphasizes the importance of electrochemical decoupling in improving the corrosion resistance of advanced materials.

Experimental study on hydrophobic properties and corrosivity of laser cleaned 7075 aluminum alloy anodized film surface

In this paper, nanosecond pulse laser was used to clean the anodic oxide film on the 7075 aluminum alloy surface. The effects of different laser energy densities (3.11–4.44 J/cm2) on the 7075 aluminum alloy surface morphology, composition, roughness, microhardness and contact angle were studied. The hydrophobicity of aluminum alloy surface after laser cleaning was studied, and the effect of laser cleaning on the corrosion resistance of aluminum alloy surface was analyzed. The results show that when the laser energy density reaches 4.44 J/cm2, the surface oxygen content of 7075 aluminum alloy is 0.37 % and the surface roughness is 0.395 μm. Laser cleaning can remove the anodic oxide film on the surface of 7075 aluminum alloy. The new surface formed after laser cleaning is acceptable without damage. Compared with mechanical removal method, under the specific laser energy density (4.44 J/cm2), the microhardness of the surface is slightly improved, while the hydrophobicity is significantly improved, which provides the feasibility of anti-corrosion for regular use after laser cleaning. This work provides basic research and practical guidance for laser cleaning of anodic oxide film on 7075 aluminum alloy surface.

Catalytic transfer hydrogenation of furfural via metal-organic framework-derived high entropy alloy catalysts at room pressure

Catalytic transfer hydrogenation (CTH), as an environmentally friendly selective hydrogenation method, has attracted great interest in the preparation of high value-added products from biomass-derived resources. Herein, the carbon-based high-entropy alloy (HEA) catalysts (PtCoNiCuZn@NC-X) were prepared via MOF derivatization, which exhibited good catalytic behavior for the CTH of furfural (FF) with isopropyl alcohol (IPA) as the hydrogen donor. The conversion of FF and selectivity of furfuryl alcohol (FOL) reached 100% at 100 °C without additional pressure via PtCoNiCuZn@NC-600 catalyst. Systematic characterization suggests that the abundance of strong acidic sites, high content of high-valent metals and appropriate alloy surface composition play a crucial role in determining the catalytic behavior. This work confirms the multi-sites synergistic catalysis of HEA, establishing structure-property correlations and revealing reaction pathways that can be extended to other CTH reactions in biomass upgrading processes.

Evaluation of Ta-Co alloys as novel high-k extreme ultraviolet mask absorber

BackgroundA plausible approach for mitigating the mask 3-D (M3D) effects observed in extreme ultraviolet (EUV) lithography is to replace the existing mask absorber with alternative materials. Absorbers with a high EUV extinction coefficient k allow for lower best focus variation (BFV) through pitch and reduced telecentricity errors (TCEs).AimWe aim to evaluate Ta-Co alloys as potential high-k mask absorbers from material suitability and imaging standpoints.ApproachWe study the film morphology, surface composition, and stability of Ta-Co alloys in mask cleaning solutions and a hydrogen environment as present in the EUV scanner to assess the material suitability from an experimental aspect. Optical constants for three selected compositions, viz., TaCo, Ta2Co, and TaCo3, were determined from EUV angle-dependent reflectivity measurements. Next, utilizing rigorous simulation software, the imaging performance of Ta-Co alloys is evaluated and compared with the reference absorber. The recommended absorber thickness for Ta-Co alloy absorbers is based upon normalized image log slope (NILS) enhancement, threshold to size, and balancing of diffraction order amplitudes. A 10 nm line and space pattern with a pitch of 20 nm and 14 nm square contact holes with a pitch of 28 nm are used for the simulation study using high numerical aperture 0.55 EUV lithography process settings. The primary imaging metrics for through pitch evaluation include NILS, TCE, and BFV.ResultsThe Ta-Co alloys exhibit a higher EUV extinction coefficient k compared with the currently used Ta-based absorber. TaCo and Ta2Co demonstrate smooth surfaces and are stable in a hydrogen environment and in mask-cleaning solutions.ConclusionTa-Co alloys allow for a reduction in M3D effects at a lower absorber thickness compared with a 60 nm Ta-based reference absorber.

Tuning the Surface Alloy Composition of Phosphorus-Promoted Ni–Co Bimetallic Nanoparticles for Selective Tandem Hydrogenation

Tuning the Surface Alloy Composition of Phosphorus-Promoted Ni–Co Bimetallic Nanoparticles for Selective Tandem Hydrogenation

Fabrication of Ni-Co film for enhancing the high-temperature corrosion resistance of interconnects in solid oxide fuel cells (SOFCs)

ABSTRACT Low-cost Ni-Co alloy coating was performed by electroplating technique to improve the high-temperature corrosion resistance of stainless steel interconnects in solid oxide fuel cells (SOFCs). The effect of plating on the surface morphology, microstructure and composition of Ni-Co alloys was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). The Ni-Co coatings were fabricated at thickness of around two microns and compared at different Ni-Co molar ratios. Corrosion performance of Ni-Co coating was evaluated in a muffle furnace under ambient atmosphere at 800℃ for 110 h. Co2NiO4 spinel oxides and Cr2O3 were found on the Ni-Co coated samples after the oxidation test. Results indicated that steel substrate corrosion protection improved with a low parabolic rate constant of 20 times after Ni-Co alloy electrodeposition coating. A smooth coating layer containing Co2NiO4 oxide with fewer defects promoted high oxidation resistance of the steel samples.

Преимущественное распыление сплава NiTi атомарными и кластерными ионами

X-ray photoelectron spectroscopy was used to study the evolution of NiTi alloy surface composition under bombardment with atomic and cluster argon ions. A strong enrichment of the surface with nickel was found for both atomic and cluster ions, which is inconsistent with contemporary understanding of preferential sputtering. Possible reasons for this result are discussed.

Oxidic structures on copper-gold alloy nanofacets

Bimetallic alloy catalysts often display superior performance to their monometallic counterparts in numerous chemical reactions, whose reactivity and selectivity primarily depend on their surface structures and chemical compositions under reaction environments. Predicting the structure and composition of alloy surfaces under reaction conditions is still challenging. In this work, using density-functional theory with ab initio thermodynamics, we examine the surface structures of the Cu-Au alloy system under different preparation and oxidative environments. We analyze the stability of thin copper oxide layers on various substrates, ranging from clean Au(111) to Au3Cu and their mixtures, and Cu overlayer structures. Our results show that the stability of the oxide layer structures strongly depend on the atomic configurations of the substrate. We also explore the possibility of using computational surface characterization methods to capture the atomic configurations and electronic structure of different interfacial regions of these substrates. Our electronic structure analysis demonstrates that controlling the concentration of surface Cu allows one to fine tune the surface electronic structure, and modulating the growth conditions to express the desired surface oxide phase may achieve the same effect. By providing an atomic-scale account, this study aims to capture the atomic configurations and electronic structure of different interfacial regions of these complex oxidic Cu/Au nanoalloys for selective oxidation reactions.

Electrochemical dealloying of porous NiTi alloy: Porosity evolution, corrosion resistance, and biocompatibility behavior

This study investigates the role and mechanism of electrochemical dealloying (ED) to decrease the nickel ion release and improve the biocompatibility of porous NiTi alloy. The potentiostatic dealloying was performed in an acidic solution, and the effect of ED duration on the surface morphology and composition of porous NiTi alloys was studied. The results indicated that the dealloying was initially started from the edges of primary pores by forming TiO2 clusters due to preferential Ni dissolution. Afterward, it progressively extended to the top surface and developed a fine porous structure. We proposed two atomistic and microstructural models to describe the evolution of the porous structure during ED treatment. The potentiodynamic polarization (PDP) and electrochemical impedance spectrometry (EIS) methods were employed to investigate the corrosion behavior of the treated specimens in a Ringer's solution. Atomic absorption spectroscopy (AAS) measurement revealed that 120 s ED treatment could decrease the concentration of released nickel ions during the PDP test from 4.2 ppm to <0.01 ppm. Additionally, the in-vitro cell culture and MTT assay showed that ED treatment could significantly improve the cell adhesion and proliferation on the surface of the NiTi alloy due to the formation of a superficial nickel-depleted layer with near superhydrophilic behavior.

Prediction of the composition of surface alloys formed via pulsed melting of preliminary deposited coatings

To date, many results of studies of surface alloys have been published, but no approaches have been developed to predict their quantitative composition that can assist to design new types of coatings. This paper proposes a methodology for prediction the atomic and mass contents of elements in the surface alloys formed by pulsed liquid-state mixing of pre-deposited films and an upper layer of a substrate. The methodology validity has been verified experimentally on the example of a Cr–Zr surface alloy that is of particular interest due to its possible use in the nuclear industry. The surface alloy has been synthesized by irradiation of a Cr/Zr film-substrate system with a low-energy high-current electron-beam (LEHCEB) of microsecond duration. The results have showed good agreement between the predicted and experimental data with an accuracy satisfactory for practical applications. Some observed discrepancies are explained by the pulse-to-pulse dispersion of the energy densities during LEHCEB irradiation.

Normal spectral emissivity study for GH3044 alloy and Ti-6Al-4V alloy

Changes in normal spectral emissivity during alloy oxidation cause large errors in radiation thermometry for aero-engines and gas turbines. To study the effect of oxidation on the normal spectral emissivity of the alloy surface, GH3044 alloy and Ti-6Al-4V alloy were selected as the research objects in this paper, and the normal spectral emissivity of the two alloys at 1.5–2.1 μm wavelength was experimentally measured during oxidation in the air for 12 h. The two alloys commonly showed an overall increasing trend with oscillation during the oxidation process, but their oscillation characteristics were significantly different. The interference effect caused by the air-oxide film interface was the main reason for the oscillation phenomenon. To explore the changes of normal spectral emissivity caused by oxide film, the composition and micromorphology of alloy surface were analyzed through X-ray diffraction (XRD) and scanning electron microscopy (SEM), and it was found that the change of the alloy surface composition and micromorphology were the main factors for the overall increase on the normal spectral emissivity. In addition, polynomial models of normal spectral emissivity versus oxidation time of the two alloy was established, which was in good agreement with the experimental results.

Atomistic Mechanisms of Binary Alloy Surface Segregation from Nanoseconds to Seconds Using Accelerated Dynamics.

Although the equilibrium composition of many alloy surfaces is well understood, the rate of transient surface segregation during annealing is not known, despite its crucial effect on alloy corrosion and catalytic reactions occurring on overlapping timescales. In this work, CuNi bimetallic alloys representing (100) surface facets are annealed in vacuum using atomistic simulations to observe the effect of vacancy diffusion on surface separation. We employ multi-timescale methods to sample the early transient, intermediate, and equilibrium states of slab surfaces during the separation process, including standard MD as well as three methods to perform atomistic, long-time dynamics: parallel trajectory splicing (ParSplice), adaptive kinetic Monte Carlo (AKMC), and kinetic Monte Carlo (KMC). From nanosecond (ns) to second timescales, our multiscale computational methodology can observe rare stochastic events not typically seen with standard MD, closing the gap between computational and experimental timescales for surface segregation. Rapid diffusion of a vacancy to the slab is resolved by all four methods in tens of nanoseconds. Stochastic re-entry of vacancies into the subsurface, however, is only seen on the microsecond timescale in the two KMC methods. Kinetic vacancy trapping on the surface and its effect on the segregation rate are discussed. The equilibrium composition profile of CuNi after segregation during annealing is estimated to occur on a timescale of seconds as determined by KMC, a result directly comparable to nanoscale experiments.

Effect of Nb on the surface composition of FeCrAl alloys after anodic polarization

XPS combined with AFM have been used to investigate the surface modifications of nuclear grade FeCrAl-xNb (x= 0, 0.5, 1.0, 1.5 wt.%) alloys, induced by anodic polarization in a simulated primary coolant. Electrochemical tests were performed to study the role of the minor element Nb on the corrosion potential and composition. The optimal content of Nb, obtained after the comparative analysis of the UHV-sputtered surface, native oxide-covered surface and anodic polarized surface, is 0.5 wt.%. This alloy presents a more compact Al-enriched oxide film consistent with a higher corrosion potential at −89 mV. The protectiveness of oxide film against the active dissolution can be improved by Nb addition, but does not increases linearly with Nb content. High resolution XPS analysis details the changes of Nb oxidized states, and provides the stratification of the oxide film containing the (hydr) oxides of Fe, Al and Cr.

Revealing the surface structure-performance relationship of interface-engineered NiFe alloys for oxygen evolution reaction

NiFe alloys are among the most promising electrocatalysts for oxygen evolution reaction (OER). However, a comprehensive study is yet to be done to reveal the surface structure-performance relationship of NiFe alloys. In particular, the role of the ultrathin surface oxide layer, which is unavoidable for pure NiFe alloys, is always neglected. Herein, a series of NiFe alloys with different Ni/Fe ratios are fabricated. It is found that different Ni/Fe ratios lead to significant differences in surface composition and structure of the NiFe alloys, and thus affect their catalytic performance. Then, the oxide/metal interface of the Ni4Fe1 alloy is tailored by adjusting the hydrogenation temperature to further understand the surface structure-activity relationship, and the optimal OER performance is achieved at the oxide/metal interfaces that have suitable surface Fe/Ni ratio and an appropriate amount of oxygen vacancies. In-situ Raman characterization shows that the Ni4Fe1 alloy with well-tailored oxide/metal interface facilitates the formation of active species. Density functional theory calculations demonstrate that the ultrathin surface oxide layers are responsible for the high catalytic activity of the NiFe alloys, and that the quantity of oxygen vacancies in the surface oxides affects the adsorption energy of O* and thus to a great extent determines the catalytic activity.

Study on Developments in Protection Coating Techniques for Steel

Steel, also known as iron alloy, is found 35% of the whole mass of the Earth. It is found in many applications due to its unique properties. Alloying elements provide the backbone support for iron, improving its mechanical, physical, chemical, and structural properties. Failure of steel is due to chemical reaction i.e., corrosion, and it is unavoidable, but it can be prolonged. Applications such as marine have a salt corrosive environment. High-temperature applications such as power plants, gas turbines components, and combustion engine components accelerate air oxidization at higher temperatures. Protection coating alters the chemical composition of alloy surfaces by using techniques like conversion coating, mechanical alloying, ion beam implantation, laser cladding, and thermochemical treatments. Protection coatings adhere to the steel surface and prevent steel from direct contact with the environment, which is formed by chemical vapor deposition, physical vapor deposition, electroplating, chemical bath, sol-gel, thermal spraying, and hot-dip coating. These coatings are used to reduce the chemical reaction in accelerated corrosion environments so that the life span of the steel is further enhanced, thereby decreasing the replacement cost. These coating methods and coating materials play a vital role in corrosion and other corrosion-associated failure protection. The coating materials like chromium and cadmium produce carcinogenic gases. Coating methods such as thermal spraying, hot-dip coating, and thermochemical treatment produce by-products that affect the environment by releasing pollutants. It is essential to choose coating materials and methods that do not influence the environment and ecosystem. In this work, processing techniques available to prepare the protective coating for steel are discussed. The methods used to enhance the properties of steel and the various real-time characterizations are also discussed. In addition, challenges and opportunities in the proposed scope are also included.

Abrasive wear study of marble dust reinforced Al7075 alloy surface composites: developed by friction stir processing

Abrasive wear study of marble dust reinforced Al7075 alloy surface composites: developed by friction stir processing

Abrasive Wear Study of Marble Dust Reinforced Al7075 Alloy Surface Composites: Developed by Friction Stir Processing

Abrasive Wear Study of Marble Dust Reinforced Al7075 Alloy Surface Composites: Developed by Friction Stir Processing

Temperature-dependent XPS studies on Ga-In alloys through the melting-point

Gallium indium alloys are known to be liquid at remarkably low temperatures. Herein, we provide X-ray photoelectron spectroscopy (XPS) studies and DFT-based ab-initio molecular dynamics (MD) calculations on the composition of the liquid alloy surface. We find that alloying Ga and In in ratios close to the eutectic composition results in only minor signal shifts of the corresponding In core levels. The topmost surface layer of the liquid alloy exhibits significant In enrichment for all measured temperatures, between 300 K to 800 K the observed enrichment slightly decreases with increasing temperature. This behavior is seen in both temperature-dependent XPS and ab-initio MD simulations. Furthermore, we investigate changes in the surface composition during the liquid-to-solid phase transition by time-dependent XPS during cooling of the alloy sample. The surface of the alloy presents an advantageous nucleation site, where we regularly observe the precipitation of indium. During cooling, the precipitation processes were followed by both XPS and by monitoring the sample temperature/heating power.

RETRACTED: Recent development in friction stir processing of aluminum alloys: Microstructure evolution, mechanical properties, wear and corrosion behaviors

In this paper, the effect of mechanical vibration with reinforcement particles namely Silicon Carbide (SiC) on microstructure, mechanical properties, wear, and corrosion behaviors of aluminum alloy surface composites fabricated via friction stir processing (FSP) was investigated. The method was entitled friction stir vibration process (FSVP). The results revealed that recrystallized fine grains formed in all processing samples as a result of dynamic recovery and recrystallization, while samples processed in friction stir vibration processing resulted in better grain refinement in the stir zone than in conventional friction stir processing. Compared to conventional friction stir processing, in friction stir vibration processing, the hardness and tensile strength increased due to microstructure modification and better reinforcing distribution. From corrosion analysis, the corrosion resistance of the friction stir vibration processed samples showed a significant increase compared to the friction stir processed specimens. The wear results indicated that the wear resistance of friction stir vibration processed specimens is higher than friction stir processed specimens due to the development of smaller grains and a more homogenous distribution of the strengthening particles as the vibration is applied.