Search Results for processing of aluminides

This article reviews the bulk deformation processes for various aluminide and silicide intermetallic alloys with emphasis on the gamma titanium aluminide alloys. It summarizes the understanding of microstructure evolution and fracture behavior during thermomechanical processing of the gamma aluminides with particular reference to production scaleable techniques, including vacuum arc and cold-hearth melting, isothermal forging, conventional hot forging, and extrusion. The selection and design of manufacturing methods, in the context of processing-cost trade-offs for gamma titanium aluminide alloys, are also discussed.

Alloys based on ordered intermetallic compounds constitute a unique class of metallic material that form long-range ordered crystal structures below a critical temperature. Aluminides, a unique class of ordered intermetallic materials, possesses many attributes like low densities, high melting points, and good high-temperature strength that make them an attractive material for high-temperature structural application. This article discusses the properties, chemical composition, corrosion resistance, processing, fabrication, alloying effects and crystallographic data of nickel aluminides (Ni3Al and NiAl), iron aluminides (Fe3Al and FeAl) and titanium aluminides (alpha-2 alloys, orthorhombic alloys, and gamma alloys).

Ordered intermetallic compounds based on aluminides and silicides constitute a unique class of metallic materials that have promising physical and mechanical properties for structural applications at elevated temperatures. This article provides useful information on mechanical and metallurgical properties, material processing and fabrication, structural applications, mechanical behavior, environmental embrittlement, alloying effects, and crystal structure of aluminides of nickel, iron, titanium, and silicides. It describes the cleavage and intergranular fracture in trialuminides.

Titanium alloys are forged into a variety of shapes and types of forgings, with a broad range of final part forging design criteria based on the intended end-product application. This article begins with a discussion on the classes of titanium alloys, their forgeability, and factors affecting forgeability. It describes the forging techniques, equipment, and common processing elements associated with titanium alloy forging. The processing elements include the preparation of forging stock, preheating of the stock, die heating, lubrication, forging process, trimming and repair, cleaning, heat treatment, and inspection. The article presents a discussion on titanium alloy precision forgings and concludes with information on the forging of advanced titanium materials and titanium aluminides.

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.

This article describes the widespread use of diffusion coatings for elevated-temperature protection of the turbine components for aircraft engines and gas turbines. The principles of pack diffusion coating, namely, aluminizing, chromizing, and siliconizing, are discussed. The article presents information on the coating formation mechanism of superalloys and explains the steps involved in a typical pack cementation process. It concludes with information on the processing procedures and properties of pack aluminized steels.

This article addresses surface cleaning, finishing, and coating operations that have proven to be effective for molybdenum, tungsten, tantalum, and niobium. It describes standard procedures for abrasive blasting, molten caustic processing, acid cleaning, pickling, and solvent and electrolytic cleaning as well as mechanical grinding and finishing. The article also provides information on common plating and coating methods, including electroplating, anodizing, and oxidation-resistant coatings.

This article reviews the corrosion behavior of intermetallics for the modeling of the corrosion processes and for devising a strategy to create corrosion protective systems through alloy and coating design. Thermodynamic principles in the context of high-temperature corrosion and information on oxidation; sulfidation; hot corrosion of NiAl-, FeAl-, and TiAl-based intermetallics; and silicides are included. The article explores the thermodynamic consideration, ordering influencing kinetics, stress-cracking corrosion, and hydrogen embrittlement of aqueous corrosion. It also explains the practical issues dealing with the corrosion problems.

Metalworking is one of the three major technologies used to fabricate metal products. This article tabulates the classification of metal forming processes. It discusses different types of metalworking equipment, including rolling mills, ring-rolling machines, and thread-rolling and surface-rolling machines. The article outlines the significant characteristics of pressing-type machines: load and energy characteristics, time-related characteristics, and accuracy characteristics. It summarizes different specialized processes such as advanced roll-forming methods, equal-channel angular extrusion, incremental forging, and microforming. The article describes the thermomechanical processing of nickel- and titanium-base alloys and concludes with information on the advancements in process simulation.

Titanium and its alloys are used in various applications owing to its high strength, stiffness, good toughness, low density, and good corrosion resistance. This article discusses the applications of titanium and titanium alloys in gas turbine engine components, aerospace pressure vessels, optic-system support structures, prosthetic devices, and applications requiring corrosion resistance and high strength. It explains the effects of alloying elements in titanium alloys as they play an important role in controlling the microstructure and properties and describes the secondary phases and martensitic transformations formed in titanium alloy systems. Information on commercial and semicommercial grades and alloys of titanium is tabulated. The article also discusses the different grades of titanium alloys such as alpha, near-alpha alloys, alpha-beta alloys, beta alloys, and advanced titanium alloys (titanium-matrix composites and titanium aluminides).

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.

Pack cementation is the most widely employed method of diffusion coating. This article briefly reviews pack cementation processes of aluminizing, chromizing, and siliconizing. It contains tables that list typical characteristics of pack cementation processes and commercial applications of pack cementation aluminizing, which is used to improve the performance of steels in high-temperature corrosive environments.

Metal-matrix composites (MMCs) are a class of materials with potential for a wide variety of structural and thermal management applications. They are nonflammable, do not outgas in a vacuum, and suffer minimal attack by organic fluids, such as fuels and solvents. This article presents an overview of the status of MMCs, and provides information on physical and mechanical properties, processing methods, distinctive features, and various types of continuously and discontinuously reinforced aluminum, magnesium, titanium, copper, superalloy, and intermetallic-matrix composites. It further discusses the property prediction and processing methods for MMCs.

Alloys intended for use in high-temperature environments rely on the formation of a continuous, compact, slow-growing oxide layer for oxidation, and hot corrosion resistance. This article focuses on the issues related to high-temperature oxidation of superalloys used in gas turbine engine applications. It discusses the general methodologies used to evaluate oxidation resistance of materials. The article describes the performance characteristics of superalloys, single-crystal superalloys, and other high-temperature materials such as refractory metals and ceramics. It discusses hot corrosion of superalloys and airfoil degradation due to deposits resulting from ingested particles or sand. The article concludes with a discussion on the limitations of testing techniques and life prediction.

The refractory metals include niobium, tantalum, molybdenum, tungsten, and rhenium. They are readily degraded by oxidizing environments at moderately low temperatures. Protective coating systems have been developed, mostly for niobium alloys, to permit their use in high-temperature oxidizing aerospace applications. This article discusses the properties, processing, applications, and classes of refractory metals and its alloys, namely molybdenum, tungsten, niobium, tantalum and rhenium. It also provides an outline of the coating processes used to improve their oxidation resistance.

This article provides a detailed discussion on heat treatment of titanium alloys such as alpha alloys, alpha-beta alloys, and beta and near-beta alloys. Common processes include stress-relief, annealing, solution treating, aging, quenching, and age hardening. It provides information on the effects of alloying elements on alpha/beta transformation. The article also discusses the heat treating procedures, and the furnaces used for heat treating titanium and titanium alloys.

This article focuses on the mechanical properties, production of titanium powder metallurgy (P/M) compacts, namely, blended elemental (BE) compacts and prealloyed (PA) compacts. It explains the postcompaction treatments of titanium P/M compacts, including heat treatment, and thermochemical processing. The article talks about the applications of titanium P/M products, namely, BE and PA products. It concludes with a short note on the future trends in titanium P/M technology.

This article discusses the various categories of nontraditional machining processes that are subdivided according to the form of energy being harnessed. These include mechanical, electrical, thermal, and chemical methods.