Protective Oxide Layer Research Articles

THE TRIBOLOGICAL CHARACTERISTIC OF WEAR IN ALLOY STEEL COMPOSITE MATERIAL

This abstract provides a concise overview of the tribological characteristics of wear in alloy steel composite materials. Alloy steel composites, consisting of steel and alloying elements, exhibit improved mechanical properties and wear resistance. This study investigates the tribological behavior, wear mechanisms, and influential factors of alloy steel composites. Experimental tests, including pin-on-disk and abrasive wear tests, analyze friction coefficients, wear rates, and microstructural observations. The research identifies adhesive, abrasive, and fatigue wear as dominant mechanisms and explores the role of protective oxide layers and solid lubricants. The findings contribute to material selection and design for enhanced wear resistance in alloy steel composite applications..

Effect of acidic solution and immersion duration on the corrosion behaviour of the aluminium 6061 alloy

The current investigation's goal is to examine the corrosion effect of aluminium 6061 alloys. The acidic immersion corrosion experiment was utilised to perform the corrosion test. The experiments were carried out in accordance with the L9 orthogonal array tables with two corrosion parameters: acidic solution and immersion duration with three levels. Taguchi’s methodology optimised the corrosion parameters to obtain a minimum corrosion rate on aluminium 6061 alloys. The results reveal that the chloride ions cause huge corrosion in the aluminium alloy samples dipped in a hydrochloric acidic solution. Meanwhile, significant possible corrosion happened in the initial stage of immersion of samples in the acidic solution. This is due to the termination of a protective aluminium oxide layer over the circumference area of the aluminium alloy. Moreover, the Taguchi technique revealed minor corrosion in the aluminium samples dipped in a nitric acidic solution (HNO3) for 216 h. Analysis of Variance (ANOVA) confirmed the contribution of two corrosion parameters on the corrosion rate of the aluminium alloy. The Scanning Electron Microscope (SEM) shows the presence of chloride traces over the surface of the highly corroded aluminium alloy.

Effect of the electrical discharge machining on Ti6Al4V corrosion behaviour in simulated body fluid

Titanium alloys, such as Ti6Al4V, are widely employed in the biomedical industry for implant applications due to their favourable properties. However, these alloys can experience long-term corrosion in the presence of bodily fluids, which is a critical concern for implants as it affects their timespan. Therefore, this study aimed to examine the corrosion resistance of Ti6Al4V in body fluid. Highly desirable electrical discharge machining (EDM) techniques used for Ti6Al4V sample preparation with three different conditions (oil, deionized water, and hydroxyapatite mixed in deionized water). Corrosion was assessed using electrochemical analyses, with microstructural analysis. Results indicated that the samples produced using water and oil had the best and lowest corrosion resistance, respectively. Protective oxide layer formed during the EDM in water while heterogeneous surface was produced for EDM in oil. The increase in capacitance leads to the thickening of the oxide layer, thereby enhancing the corrosion resistance.

Fracture toughness investigations of AA6061-SiC composites: Effect of corrosion parameters

The research gap in this problem lies in the limited understanding of how corrosion parameters, such as reinforcement composition, exposure time, and concentration of the corrosive agent, affect the fracture toughness of AA6061-SiC composites. Investigating these factors can provide valuable insights into the corrosion behaviour of AA6061-SiC composites and help optimise their mechanical properties for specific applications in harsh environments. The study aimed to optimise the parameters and find the best combination of composition, normality, and exposure time that improves fracture toughness. The study's results showed that normality (37%), and exposure time (47%) significantly affected the material's fracture toughness. Fracture toughness tests showed Case 1 had higher fracture toughness (18.35 MPa√m) due to lower normality and shorter exposure time, indicating a less aggressive corrosive environment.In contrast, Case 3 had lower fracture toughness (14.86 MPa√m) due to higher normality and longer exposure time, suggesting increased corrosion severity. In particular, increasing the exposure time and concentration of the corrosive agent decreased the fracture toughness. The composite was exposed to a 3.5% NaCl solution, which caused severe damage and formed a protective oxide layer. However, pitting corrosion occurs and causes decreasing in fracture toughness.

Impact of thermal oxidation parameters on micro-hardness and hot corrosion of Ti-6Al-3Mo-2Nb-2Sn-2Zr-1.5Cr alloy

Protective oxide layers on Ti-6Al-3Mo-2Nb-2Sn-2Zr-1.5Cr (TC21) alloy with equiaxed microstructure considerably influence micro-hardness and hot corrosion resistance. The present work’s thermal oxidation of TC21 alloy was performed at 600, 700, and 800 °C for 5, 20, and 50 h durations. Hot corrosion methods in NaCl and NaCl + Na2SO4 salt media were applied to raw (unoxidized) and oxidized samples at 600 and 800 °C for 50 h. Hot corrosion was conducted at 600 °C for 5 cycles with 10-h steps. The best oxide layer thickness was observed at 800 °C, which increased with increased oxidation time and temperature. The surface hardness of the oxide layer at 800 °C was 900 ± 60 HV0.05 owing to the formation of TiO2 and Al2O3 phases. Raw material hardness was 342 ± 20 HV0.05, increasing threefold due to thermal oxidation. In the case of NaCl, weight loss dominated all samples except at 800 °C for 5 h. In the case of NaCl + Na2SO4, weight gain occurred at 600 and 800 °C for 5 h. Weight loss occurred for the raw samples and those processed at 800 °C for 20 and 50 h, where the oxide layer flaked off. Surface hardness increased upon hot corrosion testing because of the formation of brittle phases, such as TiO2 and Na4Ti5O12. Samples that oxidized at 800 °C for 5 h had the highest hardness and corrosion resistance.

Effects of oxide layers on zirconium alloy-steam reaction

In a severe accident of a BWR plant, zirconium alloy of fuel cladding reacts with steam becoming a heat source for core melting and becoming a hydrogen source for hydrogen explosion. There are a lot of publications giving empirical formulas for energy and hydrogen production due to the zirconium alloy-steam reaction. Most of the formulas are based on a parabolic law, which means the reaction rate and hydrogen production rate decrease monotonously with the reaction time due to the protective oxide layers developed on the alloy surface. However, when the oxide layers are defective for some reason, their effectiveness against the reaction is weakened and the reaction rate will increase. In order to confirm the stability of the oxide layers, an integral-type experiment on the zirconium alloy-steam reaction was set up, hydrogen production rate due to the reaction was measured as a function of exposure time and surface temperature, and then, the oxide layers on the specimen were examined after the exposure. It was confirmed that (1) the analytical results based on Cathcart's formula well explained the experimental results, and (2) the hydrogen production rate did not decrease simply with the exposure time but the decrease in effective oxide layer density resulted in loss of protectiveness and the reaction rate increased.

Effects of Cr content on microstructure and tribological properties of laser cladding Ti-based coatings

Ti-Al-Si-SiC-Crx (X = 0, 5, 10, 15) coatings were prepared on TC4 alloy by laser cladding, and their microstructure and tribological properties were investigated. The results reveal that the coatings consist of Ti3Al, TiC, Ti5Si3, and Ti4Cr phases. In room temperature friction, with the addition of Cr, Ti4Cr soft phase was formed in the coating, which reduced the three-body wear of the coating. However, an excess of Ti4Cr soft phase induces a reduction in the wear resistance of the coating. Under high temperature friction conditions, due to the addition of Cr, a super-hard amorphous oxide protective layer is formed on the wear surface to improve the wear resistance of the coating. Therefore, Ti-Al-Si-SiC-Cr10 coating has the best tribological properties.

Architecting versatile NiFe2O4 coating for enhancing structural stability and rate capability of layered Ni-rich cathodes

Nickel-rich layered oxides are considered one of the most promising cathode materials for efficient lithium-ion batteries due to their high energy density and reasonable cost. However, at high cut-off voltage, the interfacial instability and structural degradation lead to severe capacity attenuation and poor thermal stability, which greatly hinder their large-scale applications. Herein, a multifunctional antispinel NiFe2O4 coated LiNi0.6Co0.2Mn0.2O2 (NCM@NFO) material is in-situ induced by co-precipitation and subsequent sintering, boosting the cycling stability of Ni-rich materials. Coupling in-depth characterizations (in-situ X-ray diffraction, etc.) with density functional theory calculations, the versatility of the NFO coating has been revealed. Including suppressing the transition metal dissolution, preventing the unwanted phase transition, inhibiting the oxygen vacancy generation, and stabilizing the crystal structure of the NCM by forming an M-O-N bonding network. More importantly, attributing to the high ion/electron conductivity of the NFO layer, the Li+ transport kinetics between NCM@NFO particles have been facilitated. Benefitting from the collaborative effect of the protective NFO coating, the optimized 2 wt% NFO@NCM (NCM@NFO-2) sample achieves higher capacity retention (81.25 vs 67.88% after 200 cycles) at high voltages (2.75 ∼ 4.5 V@0.5C) and more excellent rate capabilities (109.86 vs 49.52 mAh·g−1 at 10C), as well as impressive capacity retention of 81.72% after 100 cycles (at 60 °C@1C). Constructing a versatile bimetallic oxide protective layer at the secondary particle surface of layered oxides provides an effective strategy for Ni-rich cathodes towards high-energy, long-duration, and safe lithium ion batteries.

Clarifying the irradiation effect on the general oxidation of 316L stainless steel in high temperature hydrogenated water after 1000h immersion

The role of proton irradiation in the general oxidation of 316 L stainless steel in simulated PWR primary water after 1000 h immersion was clarified by comparing the microstructural and microchemical features of oxides formed on both the irradiated and un-irradiated regions of identical grains. Hence, the interference from differences in crystallographic orientation can be ruled out. Interestingly, the average inner oxide thickness on the irradiated region is significantly thinner than that on the un-irradiated region. The enhanced resistance to oxidation on the irradiated region originates from the more protective inner oxide layer and the formation of a continuous Ni-rich zone near the oxide/matrix interface. The inner oxide formed on irradiated region is less deficient in cation due to the enhanced diffusion of Cr from matrix by the irradiation-induced defects, thus making a better diffusion barrier. Meanwhile, the formation of continuous Ni-rich zone near the oxide/matrix interface, which is facilitated by the Ni-rich defects serving as nuclei, fast generation of vacancy at the interface and suppression of the outward diffusion of surplus Ni, can diminish the available space for the growth of inner oxide. The limited oxidation space and high Cr content at the oxide/matrix interface in the irradiated region result in the formation of rocksalt oxide while spinel oxide is formed near the interface in the un-irradiated region.

Wear, corrosion and oxidation characteristics of consolidated and laser remelted high entropy alloys manufactured via powder metallurgy

High entropy alloys have promising wear, oxidation, and corrosion properties compared to conventional alloys and superalloys. In the present study, CrCuFeNiAl0.5 and CrCuFeNiAl0.5Si0.5 alloys were prepared using a traditional powder metallurgy process and then remelted the surfaces via laser. The laser remelting (LR) process gains a denser and more homogeneous surface to alloys. Pressureless consolidated and laser-remelted specimens were subjected to wear, corrosion, and oxidation tests. In the wear tests, it was observed that the wear resistance of Si-containing samples was better due to higher hardness. However, the laser remelting process has mostly increased rather than reduced wear losses. The less volume loss of laser-melted samples was attributed to the almost pure Cu in its content. There is little difference among all samples in electrochemical corrosion measurements. The formation of a fragile passivation layer was observed in potentiodynamic polarization curves of CrCuFeNiAl0.5Si0.5 and LR-CrCuFeNiAl0.5Si0.5 alloys. The alloy with the best corrosion resistance is CrCuFeNiAl0.5Si0.5, whose icorr value is 0.936 × 10−6 A/cm2. After high-temperature oxidation tests, the CrCuFeNiAl0.5 alloy exhibited the worst oxidation performance due to not forming a protective oxide layer on the surface, while LR enabled the protective oxide scale in a short oxidation time. The presence of Si in this alloy relatively enhances the oxidation resistance. The best oxidation performance was observed in LR-CrCuFeNiAl0.5Si0.5 due to the forming of a protective Al2O3 layer during the oxidation tests.

Cytotoxicity of Metal Ions Released from NiTi and Stainless Steel Orthodontic Appliances, Part 1: Surface Morphology and Ion Release Variations.

Despite numerous studies on ion release from orthodontic appliances, no clear conclusions can be drawn due to complex interrelations of multiple factors. Therefore, as the first part of a comprehensive investigation of cytotoxicity of eluted ions, the objective of this study was to analyze four parts of a fixed orthodontic appliance. Specifically, NiTi archwires and stainless steel (SS) brackets, bands, and ligatures were immersed in artificial saliva and studied for morphological and chemical changes after 3-, 7-, and 14-day immersion, using the SEM/EDX technique. Ion release profiles were analyzed for all eluted ions using inductively coupled plasma mass spectrometry (ICP-MS). The results demonstrated dissimilar surface morphologies among parts of the fixed appliance, due to variations in manufacturing processes. The onset of pitting corrosion was observed for the SS brackets and bands in the as-received state. Protective oxide layers were not observed on any of the parts, but adherent layers developed on SS brackets and ligatures during immersion. Salt precipitation, mainly KCl, was also observed. ICP-MS proved to be more sensitive than SEM/EDX and exhibited results undetected by SEM/EDX. Ion release was an order-of-magnitude higher for SS bands compared to other parts, which was attributed to manufacturing procedure (welding). Ion release did not correlate with surface roughness.

Improvement of protective oxide layers formed by high-frequency plasma electrolytic oxidation on Mg-RE alloy with LPSO-phase

Oxide layers on Mg97Y2Zn1 magnesium alloy with strengthening LPSO-phase were formed by plasma electrolytic oxidation (PEO) in bipolar mode with frequency variation of forming current pulses (50 and 500 Hz) and addition of sodium aluminate or sodium silicate to alkali phosphate fluoride electrolyte. Microstructure, chemical and phase composition, corrosion and mechanical properties of the oxide layers formed were investigated. With increasing current frequency for both electrolytes, an increase in homogeneity of the oxide layers structure and a decrease in their porosity and fracturing at constant thickness were recorded. The oxide layers formed at 500 Hz even with some decrease in hardness have better adhesive strength and 2 orders of magnitude higher short-term corrosion resistance values. PEO of Mg-alloy with LPSO-phase in the electrolyte with addition of sodium aluminate in combination with increased pulse frequency (500 Hz) allows forming the best-quality uniform oxide layer with high hardness, adhesive strength and corrosion resistance properties. The use of electrolyte with addition of sodium silicate reduced the adhesive strength by 1.5 times and brought down the long-term corrosion resistance of oxide layers by an order of magnitude, as compared with the electrolyte with sodium aluminate. The reason for a significant improvement in the complex of protective properties of the oxide layers with an increase in the current pulse frequency is supposed to be a decrease in the power and duration of individual microarc discharges with simultaneous increase in their number per unit oxidized area.

Oxidation properties of complex concentrated alloys FeAlCrV and FeAlCrMo

Complex concentrated alloys (CCAs) are attracting considerable interest due to their potential applications under extreme conditions. This study focuses on two complex concentrated alloys, the FeAlCrV and the FeAlCrMo alloys, which already exhibited exceptional mechanical properties at high temperatures. In this regard, room temperature corrosion resistance and high-temperature oxidation were studied to investigate their potential applicability in harsh environments. It is shown that the corrosion resistance of both CCAs is much higher than that of AISI 304 and P91 steels in 0.5 M H2SO4 solution, while in 3.5% NaCl solution was comparable. On the contrary, high-temperature oxidation of CCAs was unsatisfactory, especially exceeding 700 °C. The intensive analysis of the formed oxide scales revealed that the protective oxide layer is not being formed at temperatures above 700 °C, primarily because of the occurrence of vanadium corrosion (FeAlCrV) and evaporation of Mo oxides (FeAlCrMo). The results of this study unambiguously showed the importance of studying oxidation properties at high temperatures parallel with the mechanical properties for the development of CCAs for cutting-edge technical applications.

Effect of Molybdenum Contents on Microstructure and High-Temperature Wear Behavior of SiMo Ductile Iron

High-silicon and molybdenum (SiMo) ductile iron is a common heat-resistant alloy that may be exposed to high-temperature wear during service in many of its applications. The wear behavior of four SiMo ductile iron alloys was evaluated at different temperatures up to 750 °C. This research focuses on the influence of various Mo contents on the microstructure, structural stability, and hence, the wear performance of such alloys. Thermodynamic calculations proposed the phase diagrams, critical transformation temperatures, and phase volume fractions in all samples by means of Thermo-Calc software. The dilatometry measurements were carried for confirming the theoretical results of Thermo-Calc thermodynamic calculations. The results revealed that the microstructure of SiMo ductile cast iron consists of nodular graphite and a ferrite matrix with carbides embedded in the fine precipitates at the grain boundary regions. The type of carbides and the nature of these fine precipitates are discussed according to EDX and SEM results. Adding molybdenum enhanced the wear performance of SiMo by decreasing the weight loss by about 40–70% compared to a Mo-free alloy. This is due to the increased molybdenum carbides, which increase hardness and improve wear resistance in SiMo alloys. The high temperatures have a negative effect on reducing the wear resistance at 250 °C. On the other hand, the wear resistance unexpectedly started to increase at higher temperatures of 500 °C and 750 °C because of the contribution of oxidative wear with abrasive wear by forming a protective oxide layer. Furthermore, the obtained results supported the idea that adding molybdenum improves wear resistance at high temperatures. Hence, SiMo has the potential to be wear-resistant material in wider applications requiring high-temperature wear resistance.

Synchronously Producing H2 and Purifying Methyl Orange-Polluted Water through the Reaction of an Al–GaInSn Alloy Plate and H2O

Hydrogen gas (H2) as a fuel has the advantages of high energy density (122 kJ g-1) and zero carbon emissions. To meet the growing demand for H2 in the future, green, efficient, and convenient production technologies must be developed. The Al-H2O reaction, which produces H2 by reacting aluminum (Al) with water (H2O), is considered a rapid method for producing H2. However, Al-H2O creates a protective oxide layer on the surface of Al, preventing the production of H2. In this study, we developed a simple method for forming Al-GaInSn alloy by brushing GaInSn-Al2O3 grease onto an Al plate to form an Al/GaInSn-Al2O3/Al sandwich structure. Al2O3 in the sample supports GaInSn, prevents the leakage of GaInSn, and promotes its penetration into the Al lattice to form Al-GaInSn alloy. By forming a liquid phase within the alloy, GaInSn increases the accessibility of Al to the reaction. As a result, the Al-GaInSn alloy can rapidly react with pure H2O to produce H2 at room temperature conditions, with yields as high as ∼93.2%. It was interesting to find that dye-polluted water (methyl orange) could be synchronically purified by the Al-H2O reaction at the same time.

First-principles study on the corrosion resistance of oxygen at Fe-Pb/Bi solid-liquid interface

Oxygen control technology is considered to be one of the most effective means to resist the dissolution corrosion of liquid metals. The mechanism for resisting the dissolution corrosion by oxygen is investigated by the interaction between oxygen and liquid metals using First-principles calculations. The energetics results indicate that O atom prevents the adsorption of Pb and Bi atoms and the escape of Fe atoms. The electronics characters of the surfaces indicate there is a trend in bonding O and Pb atoms in a certain distance, and the binding of surrounding Fe atoms is strengthened by the adsorbed O atom. These are predicted to be the initial stages of the formation of protective oxide layers. Besides, the increase in the coverage of liquid metals weakens the bond between Fe and O atoms. In addition, Pb and Bi atoms tend to migrate from the position far away from O atom to the Fe matrix by replacing Fe atoms. The O atoms that cover the surfaces uniformly are beneficial to the corrosion resistance of liquid metals. The results of energetics, electronics and dynamic calculations provide indispensable data to understand the corrosion resistance of the O atom in the environment of liquid metals.

Microstructure, thermostability and tribological behavior of composite CoCrFeNiTix high-entropy alloy coatings fabricated by laser cladding

CoCrFeNiTix (x = 0,0.25,0.5,0.75,1.0) high-entropy alloy (HEA) coatings were prepared on 45 steel by laser cladding, to explore the microstructural evolution, thermostability and the high-temperature tribological behavior of the coating. Ti-doping promotes more intergranular hard BCC phase and TiO2 intermetallics to precipitate from the ductile matrix of FCC phase, resulting in an increase in the averaged microhardness. The favorable thermostability of the heterogeneous microstructure and the oxide layer induced by friction endow the laser cladded HEA coating with excellent dry sliding wear-resistance in a wide temperature range from room temperature to 800 °C. Taking the place of the adhesive wear at room temperature, the oxidative wear becomes dominant in the wear process when the temperature exceeds 200 °C, contributing to the decrease in the wear rate before 600 °C. The formation of spherical particles on the wear track, as well as the oxide layer at elevated temperature, are revealed from the perspective of thermodynamic. It is found that the protective oxide layer is susceptive to delaminate due to the synergetic effect of strength reduction, internal stress accumulation and the destruction of the bonding, which explains the rise of the wear rate from its lower value of 1.84 × 10−5 mm3/(N·m) at 600 °C to 9.64 × 10−5 mm3/(N·m) at 800 °C.

The effect of Al and Ti on the microstructure, mechanical properties and oxidation resistance of γ′-Ni3(Al, Ti) strengthened austenitic stainless steels

Both Al and Ti are the key elements for the formation of γ′-Ni3(Al, Ti) phase and protective oxide scale in the γ′-Ni3(Al, Ti) precipitation strengthened austenitic stainless (AS) steels. To obtain good mechanical properties, especially at elevated temperatures, high volume fraction of γ′ phase is required, which is strongly dependent on the total amounts of Al and Ti. For a given concentration of (Al + Ti), changing Al or Ti addition also has significant effects on the microstructure, mechanical properties and oxidation resistance of alloys. In this study, three alloys are designed by moderately adjusting Al and Ti addition while keeping (Al + Ti) concentration constant (8.7 at.%). It is found that increasing Ti and decreasing Al addition lead to fine Laves precipitates and close spacing between them, which in turn refine grain size and enhance strength at temperature lower than 750 °C. But at about 800 °C, the strength of there alloys is almost the same. Increasing Al and decreasing Ti addition have no apparent influence on the γ′ phase but promote the formation of B2–NiAl phase, resulting in reduced ductility at elevated temperature. Besides, high Al addition facilitates the formation of continuous protective oxide layer (mainly alumina) and is beneficial for oxidation resistance at 750 °C for 500 h. As Ti replaces Al, the integrity of protective alumina layer is destroyed and the discontinuous Al-rich oxides are interlaced with Cr-rich and Ti-rich oxides.

Corrosion resistance of austenitic stainless steel using cathodic plasma electrolytic oxidation

Substantial improvement of corrosion resistance of austenitic stainless steel (SS) has been demonstrated with a protective oxide layer formed by the cathodic plasma electrolytic oxidation (CPEO) process. Two distinct layers, a porous-structured outer layer comprising Fe oxides and a compact inner layer comprising Cr oxides, were created on the SS surface after the CPEO process. The thicknesses of the outer and inner layers were approximately 7 μm and 12 μm, respectively, and the oxide layers were fabricated in an exceptionally short time of <30 s. A potentiodynamic polarization analysis exhibited a 65 % decrease in the corrosion current after the formation of the protective oxide layer, verifying the effectiveness of the CPEO treatment on the corrosion resistance of SS. An electrochemical impedance spectroscopy study revealed that the outer layer captured corrosive species due to its porous structure, while the inner layer had high resistance to reactions with corrosive species due to the compact structure of Cr oxides. Additionally, a Rockwell C indentation test demonstrated the robust mechanical property of the protective oxide layer with a strong bonding strength to the substrate.

Tribological and machining characteristics of AA7075 hybrid composites and optimizing utilizing modified PROMETHEE approach

In this research work an attempt was made to reinforce AA7075 composites with B4C and SiC particles through stir casting route. SEM with EDS mapping revealed that the reinforcement were uniformly over the composites and hardness reduces with the addition of SiC particles owing to the inverse hall petch effect. The results revealed that wear rate reduces with addition of SiC particles owing to the formation of mechanically mixed layer and protective oxide layer confirmed through SEM with EDAX mapping. Three distinct cracks were formed, when slides at different temperature as confirmed through worn surface morphology, pits cracks and plasticization of material were the other features observed. The used motor oil properties were analyzed and results divulged that the oil suitable for dielectric fluid. Increase in Material Removal Rate (MRR), reduction in Tool Wear Ratio (TWR) and Surface Roughness (Ra) was observed with the incorporation of powder particles owing to the bridging effect. Black spots, craters, micro pits, globules and micro crack are the distinct observed on the machined surface topography. The modified Preference Ranking Organization METHod for Enrichment of Evaluations (PROMETHEE) optimization technique was utilized to find the optimal parametric combination.