Showing papers on "Corrosion published in 2000"

Characterisation of oxide films produced by plasma electrolytic oxidation of a Ti–6Al–4V alloy

Abstract: The paper discusses processing and property aspects of oxide films formed on a Ti–6Al–4V alloy by AC plasma electrolytic oxidation (PEO) in aqueous solutions containing aluminate, phosphate, silicate and sulfate anions and some of their combinations. Structure, composition, mechanical tribological and corrosion resistant characteristics of the films formed are studied by SEM, XRD and microhardness analyses, and by scratch, impact, pin-on-disc friction and potentiodynamic corrosion testing. It is found that the films produced from the aluminate–phosphate electrolyte are dense and uniform and are composed mainly of Al 2 TiO 5 and TiO 2 phases of the rutile form. The films possess a beneficial combination of 50–60 μm thickness, 575 kg/mm 2 hardness and high adhesion and provide a low wear rate (3.4×10 −8 mm 3 /Nm) but a relatively high friction coefficient of μ=0.6–0.7 against steel, caused by material transfer from the counterface. A minimum friction coefficient of μ=0.18 is recorded during the testing of softer rutile–anatase films, 7 μm thick, produced from a phosphate electrolyte. Both of these types of film show good corrosion resistance in NaCl and physiological solutions, where the corrosion current is approximately 1.5 orders of magnitude lower than that of the uncoated substrate. SiO 2 /TiO 2 -based films with 70–90 μm thickness and high bulk porosity produced from silicate and silicate–aluminate electrolytes demonstrate better corrosion behaviour in H 2 SO 4 solution, due to the greater chemical stability of the film phase components in this environment.

Fundamentals of Electrochemical Corrosion

Abstract: Covering the essential aspects of the corrosion behavior of metals in aqueous environments, this book is designed with the flexibility needed for use in courses for upper-level undergraduate and graduate students, for concentrated courses in industry, for individual study and as a reference book. Contents: Overview of aqueous corrosion Electrochemical background on electrode reactions (includes use of Pourbaix diagrams) Electrochemical background on electrode kinetics How the corrosion rate is established (includes use of polarization curves) Corrosion behavior of active-passive type metals Principles and procedures of electrochemical measurements Localized corrosion phenomena and corrosion processes.

Corrosion: Understanding the Basics

Abstract: This book presents a practical "how to" approach to understanding and solving the problems of corrosion of structural materials. Although it is written mainly for those having a limited technical background in corrosion, it also provides more experienced engineers with a useful overview of the principles of corrosion and can be used as a general guide for developing a corrosion-control program. Includes identification of the various forms of corrosion, critical factors leading to a specific type of corrosion, necessary preventive steps to eliminate or reduce corrosion damage, protective-coating selection, corrosion characteristics of common structural materials, corrosion-testing programs, and failure-analysis procedures.

Current status of environmental barrier coatings for Si-Based ceramics

Abstract: Silicon-based ceramics are the leading candidates for high temperature structural components in next generation gas turbine engines. One key drawback of silicon-based ceramics for such an application is volatilization of the protective silica scale in water vapor and the resulting rapid ceramic recession. Therefore, the realization of Si-based ceramics components in advanced gas turbine engines depends on the development of protection schemes from water vapor attack. Currently, plasma-sprayed external environmental barrier coatings (EBCs) are the most promising approach. In the late 1980s and early 1990s a wide range of refractory oxide materials were tested as coatings on Si-based ceramics to provide protection from hot corrosion. After the discovery of silica volatilization in water vapor in the early 1990s, the focus of EBC development research has been shifted towards the protection from water vapor attack. Experience learned form the earlier coating developmental effort provided the foundation upon which more complex and advanced EBC coatings have been developed. This paper will discuss the brief history and the current status of EBC development for Si-based ceramics with the main focus on water vapor protection.

Porosity evaluation of protective coatings onto steel, through electrochemical techniques

Abstract: Various electrochemical techniques, usually used to characterise the corrosion resistance of coated steel, are compared in order to evaluate the porosity of various protective coatings (Al, Ti, TiN or CrN). The porosity significantly influences the corrosion behaviour of the coated steel, tested in saline environment, and some gaps are evident in the porosity values determined from these techniques. These heterogeneous data are interpreted in terms of intrinsic behaviour of each coating and of galvanic effects between the relevant coating and the substrate. The advantages and drawbacks of each electrochemical technique are underlined in correlation with the type of tested coating.

Surface modifications induced in 316L steel by laser peening and shot-peening. Influence on pitting corrosion resistance

Abstract: The influence of laser peening (LP) on the electrochemical behavior of AISI type 316L stainless steel in a saline environment was evaluated. Surface modifications were investigated as they might have beneficial effects on the corrosion behaviour. Low residual stress and work hardening levels were found, when compared with a conventional shot-peening (SP) treatment, mainly because of the absence of martensite transformation in the case of LP. Surface changes were accompanied by small roughening effects and a global preservation of the surface chemistry after treatment. Therefore, electrochemical tests performed on samples after LP and SP treatments showed increases in rest potentials, reductions of passive current densities and anodic shifts of the pitting potentials evidenced by a stochastic approach of pitting. The better pitting resistance was observed after LP treatment, which seems to reflect a reduction or an elimination of active sites for pitting at lower potentials. Even though the deleterious surface state of shot peened surfaces possibly counterbalances the beneficial influence of residual stresses, a beneficial influence of mechanical surface treatments has been demonstrated regarding the localized corrosion properties.

Stainless steel in bone surgery.

Abstract: Today, stainless steel is one of the most frequently used biomaterials for internal fixation devices because of a favorable combination of mechanical properties, corrosion resistance and cost effectiveness when compared to other metallic implant materials The biocompatibility of implant quality stainless steel has been proven by successful human implantation for decades Composition, microstructure and tensile properties of stainless steel used for internal fixation is standardized in ISO and ASTM material specifications Metallurgical requirements are stringent to ensure sufficient corrosion resistance, nonmagnetic response, and satisfactory mechanical properties Torsional properties of stainless steel screws are different from titanium screws Stainless steel bone screws are easier to handle because the surgeon can feel the onset of plastic deformation and this provides adequate prewarning to avoid overtorquing the screw New nickel-free stainless steels have been recently developed primarily to address the issue of nickel sensitivity These stainless steels also have superior mechanical properties and better corrosion resistance The Ni-free compositions appear to possess an extraordinary combination of attributes for potential implant applications in the future

Nickel, cobalt, and their alloys

Abstract: This book is a comprehensive guide to the compositions, properties, processing, performance and applications of nickel, cobalt, and their alloys. It includes all of the essential information contained in the 20-volume ASM Handbook series. Includes new or updated coverage in the following areas: Expanded corrosion coverage including guidelines for selecting the best alloy for specific environments or applications Data sheets covering the compositions, specifications, applications and properties for dozens of the most commercially important heat, corrosion and wear-resistant nickel and cobalt alloys Recent advances in superalloy development, including coatings to extend high-temperature service life Unique characteristics of nickel and cobalt which allow them to be used in special-purpose applications, e.g., magnets, controlled-expansion devices, electronics, and implants for the human body Engineering applications for nickel and cobalt coatings produced by electroplating, electroforming, electroless coating, thermal spraying, and weld surfacing. Contents include: Nickel and Its Alloys: The Nickel Industry, occurrence, recovery and consumption Uses of nickel Wrought and Cast Corrosion-Resistant Alloys Cast Heat-Resistant Ni-Cr and Ni-Cr-Fe alloys Superalloys Special-Purpose Alloys Nickel Coatings Corrosion Behavior, including performance in specific environments, Stress-Corrosion Cracking and Hydrogen Embrittlement, and High-Temperature Corrosion Fabrication and Finishing, including forming, forging, powder metallurgy, heat treating, machining, welding and brazing, cleaning and finishing, and high-temperature coatings for superalloys Metallography, Microstructures, and Phase Diagrams Cobalt and Its Alloys: The Cobalt Industry, occurrence, recovery and consumption Uses of cobalt Cobalt-base alloys Wear behavior Corrosion Behavior Fabrication Characteristics Metallography, Microstructures and Phase Diagrams.

Test methods for on site measurement of resistivity of concrete. A RILEM TC-154 Technical Recommendation

Abstract: This paper describes methods to assess concrete resistivity on site for various purposes related to corrosion and protection of reinforcement. It is based on a first draft of a RILEM Technical Recommendation. The electrical resistivity of concrete can be related to the two processes involved in corrosion of reinforcement: initiation (chloride penetration) and propagation (corrosion rate). The resistivity of a structure exposed to chloride indicates the risk of early corrosion damage, because a low resistivity is related to rapid chloride penetration and to a high corrosion rate. Once damage has occurred, resistivity is relevant for electrochemical maintenance methods. The resistivity of the near surface concrete can be measured non-destructively by placing electrodes on the concrete surface, applying a voltage and measuring the current. Several arrangements can be used: one electrode (the reinforcement is the second electrode), two electrodes, four electrodes. Practical aspects of these arrangements are discussed. Procedures for calibration are proposed. Guidelines for the interpretation and reference values for various exposures and concrete compositions are given

Influence of Water Vapor and Flow Rate on the High-Temperature Oxidation of 304L; Effect of Chromium Oxide Hydroxide Evaporation

Abstract: The effect of roman PH 2 O and flow rate on the oxidation of 304Lat 873 K in oxygen is reported. High concentrations of water vapor and highflow rates result in breakaway corrosion. The mass gain after 168 hrincreased by four to five times, compared to oxidation in dry O2. Inthe presence of H2O, the corrosion products consisted of arelatively thin (Cr,Fe)2O3 oxide plus large oxide islandsconsisting mainly of Fe2O3. A mechanism explaining theeffect of water vapor on marginal chromia formers is proposed.

Bond behavior of corroded reinforcement bars

Abstract: Corrosion of reinforcement is an international problem, causing extensive damage to various types of structures. While considerable research has been carried out on measuring the amount of corrosion and methods to slow the progress of corrosion, estimating the strength of structural members with corroded reinforcement has not received sufficient attention. The two main mechanisms for the loss of strength are loss of cross section of reinforcement and loss of bond between concrete and reinforcement. This study focuses on the loss of bond strength. Reinforcing bars embedded in concrete were subjected to accelerated corrosion using external current source. The mass loss of reinforcement varied from 0% for the control to 5.91%. The average compressive strength was 4,000 psi (28 MPa). Results indicate that it is possible to induce predetermined accelerated corrosion by passing external current; low levels of corrosion (less than 1% mass loss) improves bond strength; corrosion levels resulting in more than 1% mass loss lead to reduction in bond strength; slip at failure reduces exponentially with corrosion, even at low levels; and even after excessive corrosion, measurable bond strength exists. The results obtained in this investigation are being used for the evaluation of beam and slab specimens.

Improvement of the corrosion resistance of PVD hard coating–substrate systems

Abstract: Hard coatings play a continuously increasing role in the field of tribology as well as for decorative applications. In both areas they are often exposed to corrosive environments. While especially hard coatings exhibit a high corrosion resistance for themselves, hard coating–substrate systems may suffer from a severe corrosion attack due to the defects in the coating structure (pores, pinholes) resulting from the PVD-typical film morphology. In contrast to the huge number of investigations on the structure, properties and tribological performance of hard coatings, only limited studies exist on the corrosion behaviour of hard coating–substrate systems and attempts to improve their corrosion resistance. This paper briefly describes the corrosion mechanisms and reports characteristic examples of the system behaviour. Special emphasis is put on recent investigations in order to improve the corrosion resistance by alloying, interlayers and multilayered coating structures.

Mechanical behaviour of corroded reinforced concrete beams—Part 1: Experimental study of corroded beams

Abstract: Steel corrosion in reinforced concrete leads to crack occurrence along the reinforcement (secondary cracks), to a reduction in bond strength and a reduction in steel cross section. The purpose of this study is to determine the effect of these deteriorations on the global behaviour of reinforced concrete structural elements in their service and ultimate states. Mechanical experimentation was carried out on fourteen-year-old reinforced concrete beams, on two control elements and two corroded beams. A comparative analysis of the results obtained on the beams showed that concrete cracking in the compressive area had no significant influence on the behaviour in service of the corroded elements. However, significant modifications of service behaviour were observed, due to the degradations in the tensile zone, namely: loss of bending stiffness, dissymmetrical behaviour. Finally, the measure of the residual steel cross-section of the corroded re-bars showed that the loss of bending stiffnes due to steel corrosion cannot be merely explained in terms of steel cross-section reduction. Concerning the ultimate behaviour, the loss of steel cross-section is the main parameter which leads to a reduction of bearing capacity and ductility. Another part will explain the separate and coupling effects of bond strength and steel cross-section loss on the mechanical behaviour of corroded beams.

Method for depositing nanolaminate thin films on sensitive surfaces

Abstract: The present method provides tools for growing conformal metal nitride, metal carbide and metal thin films, and nanolaminate structures incorporating these films, from aggressive chemicals. The amount of corrosive chemical compounds, such as hydrogen halides, is reduced during the deposition of transition metal, transition metal carbide and transition metal nitride thin films on various surfaces, such as metals and oxides. Getter compounds protect surfaces sensitive to hydrogen halides and ammonium halides, such as aluminum, copper, silicon oxide and the layers being deposited, against corrosion. Nanolaminate structures (20) incorporating metal nitrides, such as titanium nitride (30) and tungsten nitride (40), and metal carbides, and methods for forming the same, are also disclosed.