This article describes the processes involved in photochemical aging and weathering of polymeric materials. It explains how solar radiation, especially in the UV range, combines with atmospheric oxygen, driving photooxidation and the development of unstable photoproducts that cause various types of damage when they decompose, including the scission of carbon bonds and polymer chains. The article illustrates some of the degradation reactions that occur in different polymers and presents an overview of the strategies used to prevent such reactions or otherwise mitigate their effects.

Tool steels are carbon, alloy, and high-speed steels that can be hardened and tempered to high hardness and strength values. This article discusses the classifications of commonly used tool steels: water-hardening tool steels, shock-resisting tool steels, cold-work tool steels, and hot-work tool steels. It describes four basic mechanisms of tool steel wear: abrasion, adhesion, corrosion, and contact fatigue wear. The article describes the factors to be considered in the selection of lubrication systems for tool steel applications. It also discusses the surface treatments for tool steels: carburizing, nitriding, ion or plasma nitriding, oxidation, boriding, plating, chemical vapor deposition, and physical vapor deposition. The article describes the properties of high-speed tool steels. It summarizes the important attributes required of dies and the properties of the various materials that make them suitable for particular applications. The article concludes by providing information on abrasive wear and grindability of powder metallurgy steels.

This article describes the general categories and metallurgy of heat treatable aluminum alloys. It briefly reviews the key impurities and each of the principal alloying elements in aluminum alloys, namely, copper, magnesium, manganese, silicon, zinc, iron, lithium, titanium, boron, zirconium, chromium, vanadium, scandium, nickel, tin, and bismuth. The article discusses the secondary phases in aluminum alloys, namely, nonmetallic inclusions, porosity, primary particles, constituent particles, dispersoids, precipitates, grain and dislocation structure, and crystallographic texture. It also discusses the mechanisms used for strengthening aluminum alloys, including solid-solution hardening, grain-size strengthening, work or strain hardening, and precipitation hardening. The process of precipitation hardening involves solution heat treatment, quenching, and subsequent aging of the as-quenched supersaturated solid solution. The article briefly discusses these processes of precipitation hardening. It also reviews precipitation in various alloy systems, including 2xxx, 6xxx, 7xxx, aluminum-lithium, and Al-Mg-Li systems.

Electrical contacts are made of elemental metals, composites, or alloys that are made by the melt-cast method or manufactured by powder metallurgy (PM) processes. PM facilitates combinations of metals that ordinarily cannot be achieved by alloying. This article describes the processing, properties, and performance of electrical contacts based on PM or hybrid composite technologies with refractory metals and compounds. These metals and compounds include tungsten, molybdenum, carbide-based composites, and silver-base composites. The article explains composite manufacturing methods, namely, PM methods, internal oxidation, and hybrid consolidation. The availability of the refractory metals and compounds in various product forms are also reviewed.

The atmosphere within a furnace chamber is a basic factor in achieving the desired chemical reactions with metals during heat treating. This article presents the fundamentals of heat treating atmospheres, and describes two groups of atmosphere control, namely, furnace atmosphere control and supply atmosphere control. The two basic types of atmospheric supply systems are generated atmospheres and nitrogen-base atmospheres. The article provides a brief overview of the gas reactions associated with oxidation and carbon control to ensure either carburization, or to prevent decarburization. It demonstrates how the carbon potential control is achieved by controlling water vapor concentration, carbon dioxide concentration, or oxygen partial pressure. The article also describes the various devices and analyzers used to monitor sampled gas from furnace atmospheres, namely, chromatographs, oxygen probes, Orsat analyzers, infrared analyzers, dewpoint analyzers, and hot-wire analyzers. Finally, it discusses the advantages, disadvantages, and limitations of these analyzers.

This article describes various quenchants, namely, water and inorganic salt solutions, polymers (polyvinyl alcohol, polyalkylene glycol, polyethyl oxazoline, polyvinyl pyrrolidone and sodium polyacrylates), quench oils, and molten salts, which are used for heat treatment of ferrous alloys. It also provides information on the steps for controlling quenching performance for polymer quenchants and oils with an emphasis on measuring quenchant performance, safety measures, and oxidation.

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.

This article focuses on the construction, operation of electric arc furnaces (EAF), and their auxiliary equipment in the steel foundry industry. It provides information on the power supply of EAF and discusses the components of the EAF, including the roof, furnace shell, spout and tap hole, water-cooling system, preheat and furnace scrap burners, and ladles. The article describes the acid and basic steelmaking practices. It discusses the raw materials used, oxidation process, methods of heat reduction, and deoxidation process in the practices. The article provides a discussion on the arc melting of iron and EAF steelmaking.

This article focuses on the internal corrosion of iron and copper in potable water. It tabulates the corrosion and water-quality problems caused by materials in contact with drinking water. The article provides a theoretical description of the reduction-oxidation reactions in water to analyze the causes of corrosion of metals in contact with water. It discusses the Langelier saturation index and the Larson index for determining corrosion in potable water systems. The article describes the two major ways of mitigation against corrosion in potable water systems. The first is to line the pipe surface physically such that water and dissolved oxygen cannot reach the metal surface and the second is to add chemical inhibitors to alter water chemistry.

In a typical semiconductor integrated circuits (SICs) component, corrosion may be observed at the chip level and at the termination area of the lead frames that are plated with a solderable metal or alloy, such as tin and tin-lead alloys that are susceptible to corrosion. This article focuses on the key factors contributing to corrosion of electronic components, namely, chemicals (salts containing halides, sulfides, acids, and alkalis), temperature, air (polluted air), moisture, contact between dissimilar metals in a wet condition, applied potential differences, and stress. It discusses the chip corrosion and oxidation of tin and tin-lead alloys (solders) in SIC. The article also addresses the corrosion of the device terminations resulting in lead (termination) tarnishing that are caused by various factors, including galvanic corrosion, chemical residues, base metal migration and plating additives.

Supercritical water oxidation (SCWO) is an effective process for the destruction of military and industrial wastes including wastewater sludge. This article discusses the unique properties of supercritical water and lists the main technological advantages of SCWO. For many waste streams, corrosion continues to be one of the central challenges to the full development of the SCWO technology. The article presents a summary of selected materials exposed to various environments as well as the observed form of corrosion in a table. It also illustrates the necessity to adopt a synergistic approach incorporating feed chemistry control, reactor design modifications, and intelligent materials selection, for mitigating degradation of SCWO systems.

Steel automotive exhaust systems suffer from various forms of corrosion. This article illustrates exhaust system components with typical upper metal skin temperatures and alloys of construction. It discusses high-temperature corrosion of automotive exhaust systems, including oxidation, hot salt attack, and thermal fatigue. The article describes the various forms of corrosion which occur at the cold end of an exhaust system. The forms of cold end exhaust corrosion, including condensate pitting corrosion, exterior salt pitting, crevice corrosion, intergranular corrosion, and galvanic corrosion.

Phosphoric acid is less corrosive than sulfuric and hydrochloric acids. This article discusses the corrosion rates of metal alloys in phosphoric acid, including aluminum, carbon steel and cast irons, stainless steels, nickel-rich G-type alloys, copper and copper alloys, nickel alloys, lead, titanium alloys, and zirconium alloys. Nonmetallic materials may be chemically attacked in some corrosive environments, which can result in swelling, hardening, or softening phenomena; extraction of ingredients; chemical conversion of the nonmetallic constituents; cross-linking oxidation; and/or substitution reactions. The article also describes the corrosion resistance of nonmetallic materials such as rubber and elastomeric materials, plastics, carbon and graphite, and ceramic materials.

The corrosion issues in the compressor, combustor and turbine sections of industrial gas turbines used in steam production generally depend on the quality of the fuel, air, and water used in the engine than on the specific industrial application. This article focuses on the forms of corrosion and their preventive measures in the compressor, combustor and turbine sections of a steam turbine. The compressor section mainly suffers from aqueous corrosion; while in case of the combustor and turbine sections, which are made of nickel-base superalloys, high-temperature environmental attack in the form of high-temperature oxidation and hot corrosion are predominant. The effect of high-temperature oxidation and hot corrosion on the mechanical properties of superalloys is also discussed.

Understanding the high-temperature corrosion behavior of alloys is an important step toward the selection of appropriate alloys for process equipment. This article briefly describes the high-temperature corrosion modes that are frequently encountered in the chemical process industry. These modes include oxidation, carburization, metal dusting, nitridation, halogen corrosion, and sulfidation.

The high-temperature corrosion processes that are most frequently responsible for the degradation of furnace accessories are oxidation, carburization, decarburization, sulfidation, molten-salt corrosion, and molten-metal corrosion. This article discusses each corrosion process, along with the corrosion behavior of important engineering alloys. It describes the corrosion of plating, anodizing, and parts of pickling equipment such as tanks, wirings and bus bars, racks, anode splines, pumps, and heaters.

Weathering steels contain deliberate additions of alloying elements intended to increase the atmospheric corrosion resistance of steel. This article provides an overview of atmospheric corrosion testing. It describes the estimation of the atmospheric corrosion behavior of weathering steels by two methods such as short-term exposure tests and calculation of a corrosion index based on the steel composition. The article highlights some generalities about corrosion mechanisms. Based on the mechanism of atmospheric corrosion resistance of weathering steel, working rules for creating the protective oxide film have evolved. The article also provides case histories that illustrate both the violations of these rules and suggestions on how to avoid certain maintenance problems that may be encountered with weathering steels.

This article provides an overview of the identification systems for various grades of wrought stainless steels, namely, the American Iron and Steel Institute numbering system, the Unified Numbering System, and proprietary designations. It elaborates on five major families of stainless steels, as defined by the crystallographic structure. These include ferritic stainless steels, austenitic stainless steels, martensitic stainless steels, and precipitation-hardening stainless steels. The mechanism of corrosion protection for stainless steels is reviewed. The article examines the effects of composition, processing, design, fabrication, and external treatments on the corrosion of stainless steels. Various forms of corrosion, namely, general, galvanic, pitting, crevice, intergranular, stress-corrosion cracking, erosion-corrosion, and oxidation, are reviewed. Corrosion testing for; corrosion in atmosphere, water, and chemical environments; and the applications of stainless steels in various industries are also discussed.

This article examines the high-temperature oxidation of silica-forming ceramics under constant temperature and cyclic conditions. The effects of water vapor, impurities, and molten salts are discussed. The article describes the oxidation and corrosion of silica-forming composites, oxide ceramics, non-silica forming nitrides, carbides, and borides. The performance of environmental barrier coatings by material type is also discussed. The article also explains the effects of oxidation and corrosion on the mechanical properties of ceramic-matrix composites. It concludes with information on high-temperature applications, wear properties, and the microscopic analyses of advanced ceramics.

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.