High-temperature exposure of materials occurs in many applications such as power plants (coal, oil, natural gas, and nuclear), land-based gas turbine and diesel engines, gas turbine engines for aircraft, marine gas turbine engines for shipboard use, waste incineration, high-temperature fuel cells, and missile components. This article discusses high-temperature corrosion in boilers, diesel engines, gas turbines, and waste incinerators. Boilers are affected by stress rupture failures, waterside corrosion failures, fireside corrosion failures, and environmental cracking failures. Contamination of combustion fuel in diesel engines can cause high-temperature corrosion. Gas turbine engines are affected by hot corrosion. Refractory-lined incinerators and alloy-lined incinerators are discussed. The article provides case studies for each component failure.

This article provides an overview of key abradable thermal spray coating systems based on predominant function and key design criteria. It describes two families of coatings which have evolved for use at higher temperature: flame (combustion)-sprayed abradable powders and atmospheric plasma-sprayed abradable powders. Three classic examples of flame spray abradables are nickel-graphite powders, NiCrAl-bentonite powders, and NiCrFeAl-boron nitride powders. The article provides information on various abradable coating testing procedures, namely, abradable incursion testing; aging, corrosion, thermal cycle and thermal shock testing; hardness testing; and erosion resistance testing.

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 reviews some of the trends in superalloy development as they relate to U.S. strategic materials availability and the aerospace industry. It discusses the supply sources and availability of strategic materials and summarizes the status of U.S. resources and reserves. The article presents a list of several superalloys that have been used in gas turbine engines or that are emerging as replacements because of the promise of increased operating temperatures and higher efficiencies for the aircraft of the future. It concentrates on the objectives, results, and methodology of the NASA Conservation of Strategic Aerospace Materials (COSAM) program.

Superalloys are predominantly nickel-base alloys that are strengthened by solid-solution elements including molybdenum, tungsten, cobalt, and by precipitation of a Ni 3 (Al, Ti) type compound designated as gamma prime and/or a metastable Ni 3 Nb precipitate designated as gamma double prime. This article provides a discussion on the conventional processing, compositions, characteristics, mechanical properties, and applications of powder metallurgy (PM) superalloys. The conventional processing of PM superalloys involves production of spherical prealloyed powder, screening to a suitable maximum particle size, blending the powder to homogenize powder size distribution, loading powder into containers, vacuum outgassing and sealing the containers, and consolidating the powder to full density. PM superalloys include Rene 95, IN-100, LC Astroloy, Udimet 720, N18, ME16, RR1000, Rene 88DT, PA101, MERL 76, AF2-1DA, Inconel 706, AF115, and KM4. The article reviews specialized PM superalloy processes and technical issues in the usage of PM superalloys.

This article includes a collection of color images that aid in the identification and classification of forms of corrosion in industries and environments. It emphasizes the negative aspects of corrosion and examines the cost and the effort to test, evaluate, simulate, and prevent corrosion. The ability of corrosion to undo the best complex engineered systems has been documented.

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.

Oxide - dispersion - strengthened (ODS) materials utilize extremely fine oxide dispersion for strengthening, such as nickel-base alloys or alumina. The processing techniques employed in the production of ODS alloys produce some entrapped gases, which tend to create porosity during welding that can be rectified by suitable designing considerations. This article discusses certain successful design strategies employed in joining ODS alloys in consideration with the grain structure. It further provides a brief discussion on different welding processes involved in joining ODS materials, namely, gas-tungsten arc welding, gas-metal arc welding, electron-beam and laser-beam welding, resistance welding, furnace brazing, friction welding, and explosion welding.

The success of a reliable non-destructive evaluation (NDE) application depends greatly on the expertise and thoroughness of the NDE engineering that is performed. This article discusses the general considerations of NDE in terms of NDE response and NDE system management and schedule. It describes the NDE engineering and NDE process control, along with some case studies related to the applications of NDE. The article reviews various models for predicting NDE reliability, such as ultrasonic inspection model, eddy current inspection model, and radiographic inspection model. It concludes with an example that illustrates the integration of an ultrasonic reliability model with a CAD system.

Vapor-deposition processes fall into two major categories, namely, physical vapor deposition (PVD) and chemical vapor deposition (CVD). This article describes major deposition processes such as sputtering, evaporation, ion plating, and CVD. The list of materials that can be vapor deposited is extensive and covers almost any coating requirement. The article provides a table of some corrosion-resistant vapor deposited materials. It concludes with an overview of the applications of CVD and PVD coatings and a discussion on coatings for graphite, the aluminum coating of steel, and alloy coatings for aircraft turbines, marine turbines, and industrial turbines.

Aging is a process where the structural and/or functional integrity of components will be continuously degraded by exposure to the environmental conditions under which they are operated. This article discusses aging mechanisms in various components of military systems such as structural parts, engines, and subsystems. It describes the aging management processes such as full-scale structural testing and practical life-enhancement methods. The article reviews control and prevention systems such as usage and health monitoring systems necessary to provide effective corrosion maintenance on military systems. Failure prediction techniques, namely, the equivalent pre-crack size approach, life-cycle cost modeling and simulation, and holistic life-prediction methodology are also discussed.

The primary motivation for the insertion of metal-matrix composites (MMCs) into aeronautical systems is the excellent balance of specific strength and stiffness offered by MMCs. This article provides information on the aerostructural, aeropropulsion, and aeronautical subsystem applications of MMCs. The applications include ventral fin, fuel access door covers, helicopter blade sleeve, fan exit guide vane, nozzle actuator piston rod, nozzle actuator links, T-1 racks, and hydraulic manifold.

The primary fossil fuels are generally defined as coal, oil, natural gas, tar sands, and shale oil. This article discusses the characteristics and the types of fuels used in fossil and fuel industries. It describes the energy conversion in fuels and outlines the efficiency of a heat engine with the help of the Carnot equation.

Thermal spray is a generic term for a group of coating processes used to apply metallic, ceramic, cermet, and some polymeric coatings for a broad range of applications. This article provides a brief description of commercially important thermal spray processes, namely, powder-fed flame spray, wire- or rod-fed flame spray, electric arc spray, plasma arc spray, vacuum plasma spray, high-velocity oxyfuel spray, detonation gun deposition, and cold spray, and their advantages. It provides details on the microstructural characteristics of thermal spray coatings. The article also presents information on a wide variety of materials that can be thermal sprayed, such as metals, ceramics, intermetallics, composites, cermets, polymers, and functionally gradient materials. Tables are included, which list the thermal spray processes and coating properties of importance for various industrial applications.

Directionally solidified (DS) and single-crystal (SX) superalloys and process technology are contributing to significant advances in turbine engine efficiency and durability. These gains are expected to arise from the development of higher creep strength and improved oxidation-resistant SX alloy compositions as well as from the development of SX casting and fabrication technology to utilize advanced transpiration-cooling schemes. This article provides a detailed discussion on the chemistry and castability of first- and second-generation DS and SX superalloys. It summarizes the chemistry modifications applied to MAR-M 247 to develop CMSX-2 with respect to function and objectives. The article also lists the nominal compositions of first- and second-generation DS and SX superalloys.

This article is a comprehensive collection of properties, compositions, and applications of standard grades of titanium and selected titanium alloys. It provides data regarding the common names, Unified Number System numbers, composition limits, typical uses with service temperatures, precautions in use, and general corrosion behavior of each. The applications of titanium alloys include aerospace, gas turbine engines and prostheses. Further, the article graphically presents a comparative study of fatigue, creep and tensile properties of various titanium alloys.

This article describes the various environments affecting corrosion performance, corrosion protection, and corrosion control. These include freshwater environments, marine environments, and underground environments. The article provides information on corrosion in military environments and specialized environments, representing less-well-known environments with more limited applications.

This article provides an overview of the structural design process and discusses the life-limiting factors, including material defects, fabrication practices, and stress. It details the role of a failure investigator in performing nondestructive inspection. The article provides information on fatigue life assessment, elevated-temperature life assessment, and fitness-for-service life assessment.

With regard to documentation and photography of a catastrophic event, the field investigator's duties are fundamentally different from those of the laboratory-based analyst, even though both share the same goals. This article presents a case study on documentation considerations during the field investigation. It provides a detailed discussion on the general procedure to downselect from a multicomponent assemblage to a set of potential primary failed components. The article describes visual examination in macrofractography.

Liquid impingement erosion has been defined as progressive loss of original material from a solid surface due to continued exposure to impacts by liquid drops or jets. This article focuses on the core nature of erosion by liquid impingement, due to the greater appreciation of the distinctions between the different forms of erosion. It discusses steam turbine blade erosion, aircraft rain erosion, and rain erosion of wind turbine blades. The article describes the mechanisms of liquid impact erosion and time dependence of erosion rate. It reviews critical empirical observations regarding both impingement variables (velocity, impact angle, droplet size, and physical properties of liquids) and erosion resistance of materials, including the correlation between erosion resistance and mechanical properties and the effects of alloying elements and microstructure. The article also provides information on the ways to combat erosion.