Search Results for oxidative stress

This article describes the corrosion resistance and ion release from main transition metallic bearings used as medical devices. It discusses the main issues associated with the in vivo presence of ions and their biocompatibility during the exposure of patients to different aspects of ion toxicity. These include ion concentration and accumulation in organisms, reactive oxygen species and oxidative stress, and carcinogenicity stimulated by the corrosion process and toxic ions release.

This article examines the characteristics and behavior of scale produced by various types of oxidation. The basic models, concepts, processes, and open questions for high-temperature gaseous corrosion are presented. The article describes the development of geometrically induced growth stresses, transformation stresses, and thermal stresses in oxide scales. It discusses the ways in which stresses can be relieved. The article provides information on catastrophic oxidation, internal oxidation, sulfidation, alloy oxidation, selective oxidation, and concurrent oxidation. It illustrates the relationships between scale morphologies on binary alloys and concludes with a discussion on metal dusting and chlorine corrosion.

Structural alloys are commonly subjected to a variety of thermal and thermomechanical loads. This article provides an overview of the experimental methods in thermal fatigue (TF) and thermomechanical fatigue (TMF) and presents experimental results on the structural materials that have been considered in TF and TMF research. Life prediction models and constitutive equations suited for TF and TMF are covered. The structural materials discussed include carbon steels, low-alloy steels, stainless steels, aluminum alloys, and nickel-base high-temperature alloys. The article explains crack initiation and crack propagation in TF and TMF. It describes thermal ratcheting and thermal shock behavior of structural metallic materials. The article concludes with information on life prediction of structural materials under TF and TMF.

Bending fatigue of carburized steel components is a result of cyclic mechanical loading. This article reviews the alloying and processing factors that influence the microstructures and bending fatigue performance of carburized steels. These include austenitic grain size, surface oxidation, retained austenite, subzero cooling, residual stresses, and shot peening. The article describes the analysis of bending fatigue behavior of the steels based on S-N curves that represents a stress-based approach to fatigue. It discusses the types of specimen used to evaluate bending fatigue in carburized steels. The stages of fatigue and fracture of the steels, namely crack initiation, stable crack propagation, and unstable crack propagation, are reviewed. The article analyzes the intergranular fracture at the prior-austenite grain boundaries of high-carbon case microstructures that dominates bending fatigue crack initiation and unstable crack propagation of direct-quenched carburized steels.

Metals can react chemically with oxygen when exposed to air. Essential to an understanding of the gaseous corrosion of a metal are the crystal structure and the molar volume of the metal on which the oxide builds, both of which may affect growth stresses in the oxide. This article presents crystal structures and thermal properties of pure metals and oxides in a tabular form. The free energy of reaction, which describes the oxidation process of a pure divalent metal, is presented. The article illustrates the Richardson-Jeffes diagram, which is used in the determination of the standard Gibbs energy change of formation of oxides and the corresponding dissociation pressures of the oxides as a function of temperature. It demonstrates the Kellogg diagram which shows stability range in more complicated multioxidant systems. The article explains the determination of partial pressures of gas mixtures and partial pressures of volatile oxidation products.

Material properties are the link between the basic structure and composition of the material and the service performance of a part or component. This article describes the most significant properties that must be considered when choosing a metal for a given application, namely physical properties (mass characteristics and thermal, electrical, magnetic, radiation, and optical properties), chemical properties (corrosion and oxidation resistance) and mechanical properties (tensile and yield strength, elongation, toughness, hardness, creep, and fatigue). The article also contains tables that list room-temperature physical properties, vapor pressures, and mechanical properties for various metals.

The overarching goal of life-prediction research is to develop models for the various types of time dependencies in the crack-tip damage accumulation that occur in materials subjected to elevated temperatures. This article focuses on describing the models based on creep, oxidation kinetics, evolution of crack-tip stress fields due to creep, oxygen ingress, and change in the microstructure. It also provides a summary of creep-fatigue modeling approaches.

High temperature corrosion may occur in numerous environments and is affected by factors such as temperature, alloy or protective coating composition, time, and gas composition. This article explains a number of potential degradation processes, namely, oxidation, carburization and metal dusting, sulfidation, hot corrosion, chloridation, hydrogen interactions, molten metals, molten salts, and aging reactions including sensitization, stress-corrosion cracking, and corrosion fatigue. It concludes with a discussion on various protective coatings, such as aluminide coatings, overlay coatings, thermal barrier coatings, and ceramic coatings.

Cast stainless steels are usually specified on the basis of composition by using the alloy designation system established by the Alloy Casting Institute. This article discusses the corrosion behavior of heat-resistant alloys due to oxidation, sulfidation, and carburization. It describes the influence of the metallurgy of corrosion-resistant stainless steels on general corrosion, intergranular corrosion, localized corrosion, corrosion fatigue, and stress corrosion.

This article focuses on the life assessment methods for elevated-temperature failure mechanisms and metallurgical instabilities that reduce life or cause loss of function or operating time of high-temperature components, namely, gas turbine blade, and power plant piping and tubing. The article discusses metallurgical instabilities of steel-based alloys and nickel-base superalloys. It provides information on several life assessment methods, namely, the life fraction rule, parameter-based assessments, the thermal-mechanical fatigue, coating evaluations, hardness testing, microstructural evaluations, the creep cavitation damage assessment, the oxide-scale-based life prediction, and high-temperature crack growth methods.

Oxide dispersion-strengthened (ODS) alloys are produced by mechanical alloying, a process by which base metals and alloying particles are powdered together forming a metal-matrix composite. This article discusses the production of ODS superalloy powders and subsequent processing steps, including consolidation, hot rolling, heat treating, and the fabrication of mill products. It also discusses the nominal composition and microstructure of commercial ODS alloys, including nickel, iron, and aluminum-base systems, and provides detailed information on their mechanical, physical, oxidation, and hot-corrosion properties.