Résistance à la corrosion et comportement électrochimique des composites matriciels intermétalliques Fe₃Al renforcés par TiC

Le comportement à la corrosion de deux revêtements composites à matrice intermétallique Fe₃Al préparés par la technique HVOF (High Velocity Oxy Fuel) a été étudié dans une solution à 3.5% en poids de NaCl et comparé au Fe₃Al non renforcé. En outre, le chrome en tant qu'élément d'alliage utilisé dans la charge d'alimentation de HVOF pour évaluer l'effet du chrome sur le comportement à la corrosion du revêtement. Les techniques électrochimiques, y compris la polarisation potentiodynamique, le potentiel de circuit ouvert (OCP) et la spectroscopie d'impédance électrochimique (EIS) ont été considérées. La surface de l'échantillon a été analysée après la corrosion en utilisant un microscope électronique à balayage (MEB) et une spectroscopie photoélectronique par rayons X (XPS). L'essai de potentiel en circuit ouvert a révélé qu'il existe sur le revêtement une couche d'oxyde qui pourrait être due à la technique HVOF utilisant de l'oxygène gazeux pour appliquer les revêtements. Les diagrammes de polarisation potentiométrique ont révélé que l'ajout de particules de TiC à la matrice Fe₃Al améliore les performances de corrosion de Fe₃Al, de sorte que les revêtements Fe₃Al / TiC présentent un taux de corrosion légèrement 6 fois supérieur. Une spectroscopie d'impédance électrochimique a été réalisée pour étudier les mécanismes de prévention de la corrosion des revêtements et un mécanisme différent était supposé pour Fe₃Al-Cr / TiC. Une analyse post-corrosion, telle que les spectres XPS et les images MEB de la couche passive, a été réalisée pour étudier la forme de corrosion. L'analyse élémentaire de la couche passive a révélé que l'addition de chrome au revêtement composite, fournit une couche passive plus protectrice en bloquant les sites d'entrée des ions chlorure. Essais de polarisation cyclique effectués dans une solution d'acide sulfurique 0.25 M pour étudier le comportement de passivation et de piqûration de revêtements dans une solution différente pour comparer les résultats de plusieurs autres travaux sur des aluminiures de fer avec Fe₃Al et deux revêtements composites de Fe₃Al /TiC et Fe₃Al-Cr/TiC. Les résultats de la polarisation cyclique potentiodynamique ont révélé que les performances de corrosion des revêtements composites dans cette solution sont légèrement meilleures que Fe₃Al. Cependant Fe₃Al-Cr/TiC présente une résistance à la piqûration inférieure à celle de deux autres revêtements.The corrosion behavior of two Fe₃Al intermetallic matrix composite coatings (Fe₃Al/TiC and Fe₃AlCr/TiC) that prepared by high velocity oxy fuel (HVOF) technique was studied in 3.5 wt.% NaCl solution and compared with non-reinforced Fe₃Al. Furthermore, chromium as an alloying element used in the feedstock of HVOF to evaluate the effect of chromium on corrosion behaviour of the coating. Four electrochemical techniques, open circuit potential potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) were employed to examine corrosion behavior in detail. Post-corrosion analysis was done using Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS) to reveal the surface morphology and chemistry of the corroded samples. Results from the open circuit potential test revealed that an oxide layer formed on the coating which could be due to oxidation during the HVOF coating process. The Potentiodynamic polarization graphs revealed that adding TiC particles to Fe₃Al matrix improved the corrosion performance of Fe₃Al so that the Fe₃Al/TiC coatings exhibit slightly six times more corrosion rate. The EIS results indicated a more compact corrosion layer formed on the Cr-added coating resulting into the highest coating resistance. This is supported by the SEM/EDS and XPS analyses which revealed that a mixed oxide and hydroxide formed a passive layer. The Cr in the composite coating took the role in providing a more protective passive layer by blocking the entry sites of Clions. The pitting resistance of the Fe₃Al-Cr/TiC coating in 0.25 M H₂SO₄ solution was, however, lower compared to that of the two other coatings. It is concluded that the addition of TiC particles to Fe₃Al matrix, which primarily done for improving wear resistance, improves the corrosion resistance of the coating in saline solution. The addition of Cr into the Fe₃Al/TiC composite coating further improves its corrosion resistance, but the pitting resistance is not improved when tested in acid solution

Corrosion behavior of WC-Co coatings deposited by cold gas spray onto AA 7075-T6

This work reports a morphological, mechanical, and corrosion resistance characterization of WC-12Co and WC-25Co coatings deposited by cold gas spray (CGS) onto AA 7075-T6 alloy. Cross-sectional images of the coatings revealed dense structures with low porosities. The coating thicknesses were 65 mu m for WC-12Co and 118 pm for WC-25Co. XRD analysis showed that no fragile phases were formed in the coatings. SEM images and electro-chemical results obtained after 700 h exposure to NaCl solution showed that WC-25Co exhibited better corrosion resistance performance. The WC-12Co and WC-25Co coatings withstood 1000 and 3000 h of salt fog spray test, respectively

Advances in Organic Corrosion Inhibitors and Protective Coatings

The interaction of metal with its environment that results in its chemical alteration is called metallic corrosion. According to the literature, corrosion is classified to two types: uniform and localized corrosion. Intervention in either in the alloy environment or in the alloy structure can provide the corrosion protection of metallic materials. Furthermore, the interference in the metal alloy environment can be conducted with the utilization of cathodic or anodic protection via the corresponding inhibitors. Therefore, the most common categorization is cathodic, anodic, and mixed-type inhibitors, taking into account which half-reaction they suppress during corrosion phenomena. The majority of the organic inhibitors are of mixed type and perform through chemisorption. In order to update the field of the corrosion protection of metal and metal alloys with the use of organic inhibitors, a Special Issue entitled "Advances in Organic Corrosion Inhibitors and Protective Coatings" is introduced. This book gathers and reviews a collection of ten contributions (nine articles and one review), from authors from Europe, Asia, and Africa, that were accepted for publication in this Special Issue of Applied Sciences

Corrosion Behavior Of Al-Al2O3 Composites In Aerated 3.5% Chloride Solution

Trabajo de investigaciónAborda los compuestos de matriz metálica de aluminio encuentran muchas aplicaciones en ingeniería. Sin embargo, su comportamiento a la corrosión es incierto, especialmente en ambientes marinos. Mientras se realizan esfuerzos para mejorar su resistencia a la corrosión del AI-AI2O3, los mecanismos de corrosión aún están en discusión. En este estudio, el comportamiento a la corrosión de las aleaciones AI-Cu procesadas por pulvimetalurgia reforzadas con 10, 15 , 20 y 25 % de partículas de alúmina en volumen fueron evaluadas en una solución airada al 3.5% de NaCI usando mediciones micro estructurales y electroquímicas.Trabajo de investigació

Corrosion Resistance

The book has covered the state-of-the-art technologies, development, and research progress of corrosion studies in a wide range of research and application fields. The authors have contributed their chapters on corrosion characterization and corrosion resistance. The applications of corrosion resistance materials will also bring great values to reader's work at different fields. In addition to traditional corrosion study, the book also contains chapters dealing with energy, fuel cell, daily life materials, corrosion study in green materials, and in semiconductor industry

Experimental study of reverse crevice corrosion of copper

Crevice corrosion generally occurs on the crevice surface while the exterior or bold surfaces are not damaged. However, for copper and its alloys, the opposite is true; the bold surface is corroded while the crevice remains relatively corrosion-free. This unique type of corrosion is referred to as reverse crevice corrosion (RCC). In this research, commercially pure copper was chosen as the target metal to investigate RCC. Based on electrochemical measurements and surface analysis, reverse crevice corrosion was found to occur at room temperature. At elevated temperature only uniform corrosion was observed while under a deoxygenated environment, as expected, no corrosion was observed. A multiple crevice assembly and a working electrode were designed especially for this research. Exposure test experiments were first performed at room temperature and 50 ºC. Several types of electrochemical tests were conducted including open circuit potential measurement, potentiodynamic measurement and electrochemical impendence spectroscopy (EIS). Atomic Force Microscopy (AFM) and Raman Spectroscopy were used to analyze the surfaces of the copper coupon.The results of the exposure tests showed that RCC occurred at room temperature, but not at elevated temperature. Only uniform corrosion was observed at elevated temperature and no corrosion was occurred under a deoxygenated environment. It was found, based on the open circuit potential measurement, that the RCC process can be divided into three steps, a uniform corrosion phase, a corrosion slow-down step and a reverse crevice corrosion step. The first two steps can be combined into one phase, incubation phase. This hypothesis is supported with the results from Raman spectra and AFM. The EIS measurements revealed that the diffusion process from bulk solution to copper coupon surface is the rate controlling step for incubation phase and this diffusion process combined with the reduction of Cu (I) oxide in the crevice are the rate-controlling step corresponding to the last step

Corrosion and Protection of Metals

Introduction and Scope—During the last few decades, an enormous effort has been made to understand corrosion phenomena and their mechanisms, and to elucidate the causes that dramatically influence the service lifetime of metal materials. The performance of metal materials in aggressive environments is critical for a sustainable society. The failure of the material in service impacts the economy, the environment, health, and society. In this regard, corrosion-based economic losses due to maintenance, repair, and the replacement of existing structures and infrastructure account for up to 4% of gross domestic product (GDP) in well developed countries. One of the biggest issues in corrosion engineering is estimating service lifetime. Corrosion prediction has become very difficult, as there is no direct correlation with service lifetime and experimental lab results, usually as a result of discrepancies between accelerated testing and real corrosion processes. It is of major interest to forecast the impact of corrosion-based losses on society and the global economy, since existing structures and infrastructure are becoming old, and crucial decisions now need to be made to replace them. On the other hand, environmental protocols seek to reduce greenhouse effects. Therefore, low emission policies, in force, establish regulations for the next generation of materials and technologies. Advanced technologies and emergent materials will enable us to get through the next century. Great advances are currently in progress for the development of corrosion-resistant metal materials for different sectors, such as energy, transport, construction, and health. This Special Issue on the corrosion and protection of metals is focused on current trends in corrosion science, engineering, and technology, ranging from fundamental to applied research, thus covering subjects related to corrosion mechanisms and modelling, protection and inhibition processes, and mitigation strategies

Electrochemical and Corrosion Behavior of Metallic Glasses

Metallic glasses are multi-component metallic alloys with disordered atomic distribution unlike their crystalline counterparts with long range periodicity in arrangement of atoms. Metallic glasses of different compositions are being commercially used in bulk form and as coatings because of their excellent corrosion resistance. This book was written with the objective of providing a comprehensive understanding of the electrochemical and corrosion behavior of metallic glasses for a wide range of compositions. Corrosion in structural materials leads to rapid deterioration in the performance of critical components and serious economic implications including property damage and loss in human life. Discovery and development of metallic alloys with enhanced corrosion resistance will have a sizable impact in a number of areas including manufacturing, aerospace, oil and gas, nuclear industry, and load-bearing bioimplants. The corrosion resistance of many metallic glass systems is superior compared to conventionally used alloys in different environments. In this book, we discuss in detail the role of chemistry, processing conditions, environment, and surface state on the corrosion behavior of metallic glasses and compare their performance with conventional alloys. Several of these alloy systems consist of all biocompatible and non-allergenic elements making them attractive for bioimplants, stents, and surgical tools. To that end, critical insights are provided on the bio-corrosion response of some metallic glasses in simulated physiological environment

Electrochemical and Corrosion Behavior of Metallic Glasses

Metallic glasses are multi-component metallic alloys with disordered atomic distribution unlike their crystalline counterparts with long range periodicity in arrangement of atoms. Metallic glasses of different compositions are being commercially used in bulk form and as coatings because of their excellent corrosion resistance. This book was written with the objective of providing a comprehensive understanding of the electrochemical and corrosion behavior of metallic glasses for a wide range of compositions. Corrosion in structural materials leads to rapid deterioration in the performance of critical components and serious economic implications including property damage and loss in human life. Discovery and development of metallic alloys with enhanced corrosion resistance will have a sizable impact in a number of areas including manufacturing, aerospace, oil and gas, nuclear industry, and load-bearing bioimplants. The corrosion resistance of many metallic glass systems is superior compared to conventionally used alloys in different environments. In this book, we discuss in detail the role of chemistry, processing conditions, environment, and surface state on the corrosion behavior of metallic glasses and compare their performance with conventional alloys. Several of these alloy systems consist of all biocompatible and non-allergenic elements making them attractive for bioimplants, stents, and surgical tools. To that end, critical insights are provided on the bio-corrosion response of some metallic glasses in simulated physiological environment