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.

High-temperature corrosion can occur in numerous environments and is affected by various parameters such as temperature, alloy and protective coating compositions, stress, time, and gas composition. This article discusses the primary mechanisms of high-temperature corrosion, namely oxidation, carburization, metal dusting, nitridation, carbonitridation, sulfidation, and chloridation. Several other potential degradation processes, namely hot corrosion, hydrogen interactions, molten salts, aging, molten sand, erosion-corrosion, and environmental cracking, are discussed under boiler tube failures, molten salts for energy storage, and degradation and failures in gas turbines. The article describes the effects of environment on aero gas turbine engines and provides an overview of aging, diffusion, and interdiffusion phenomena. It also discusses the processes involved in high-temperature coatings that improve performance of superalloy.

This article is an atlas of fractographs that covers nickel-base superalloys. The fractographs display the following: hydrogen-embrittlement fracture; segment of a fractured second-stage gas-turbine wheel; gas-producer turbine rotor cast; dendritic stress-rupture fracture surface; fatigue and creep fractures; simultaneous metallographic-fractographic evaluation; and effect of thermal cycling on fatigue fracture.

The design process for ceramic materials is more complex than that of metals because of low-strain tolerance, low fracture toughness and brittleness. The application of structural ceramics to engineering systems hinges on the functional benefits to be derived and is manifested in the conceptual design for acceptable reliability. This article discusses the design considerations for the use of structural ceramics for engineering applications. It describes the conceptual design and deals with fast fracture reliability, lifetime reliability, joints, attachments, interfaces, and thermal shock in detailed design procedure. The article provides information on the proof testing of ceramics, and presents a short note on public domain software that helps determine the reliability of a loaded ceramic component. The article concludes with several design scenarios for gas turbine components, turbine wheels, ceramic valves, and sliding parts.

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.

Structural applications for advanced ceramics include mineral processing equipment, machine tools, wear components, heat exchangers, automotive products, aerospace components, and medical products. This article begins with an overview of the wear-resistant applications and the parameters affecting wear of ceramics, namely, hardness, thermal conductivity, fracture toughness, and corrosion resistance. The next part of the article addresses temperature-resistant applications of advanced ceramics. Specific applications of ceramic materials addressed include cutting tools, pump and valve components, rolling elements and bearings, paper and wire manufacturing, biomedical implants, heat exchangers, adiabatic diesel engines, advanced gas turbines, and aerospace applications.

Superalloys are nickel, iron-nickel, and cobalt-base alloys generally used for high-temperature applications. Superalloys are used in aircraft, industrial, marine gas turbines, nuclear reactors, spacecraft structures, petrochemical production, orthopedic and dental prostheses, and environmental protection applications. This article discusses the material characteristics, phases, structures, and systems of superalloys. It describes the processing of superalloys, including primary and secondary melting, deformation processing (conversion), powder processing, investment casting, and joining methods. The article also describes the properties, microstructure, and thermal exposure of superalloys. It further discusses the effects of environmental factors on superalloys, including oxidation and hot corrosion. Protective coatings are also discussed. The article provides information on the mechanical properties and chemical composition of nickel, iron, and cobalt-base superalloys in both the cast and wrought forms.

Although stainless steel is naturally passivated by exposure to air and other oxidizers, additional surface treatments are needed to prevent corrosion. Passivation, pickling, electropolishing, and mechanical cleaning are important surface treatments for the successful performance of stainless steel. This article describes the surface treatment of stainless steels including abrasive blast cleaning, acid pickling, salt bath descaling, passivation treatments, electropolishing, and the necessary coating processes involved. It also describes the surface treatment of heat-resistant alloys including metallic contaminant removal, tarnish removal, oxide and scale removal, finishing, and coating processes.

This article is a general introduction to surface engineering of engineering components, providing an overview of the applications of surface treatments and the environmental protection regulations directly or indirectly related to surface engineering processes.

The principal types of elevated-temperature mechanical failure are creep and stress rupture, stress relaxation, low- and high-cycle fatigue, thermal fatigue, tension overload, and combinations of these, as modified by environment. This article briefly reviews the applied aspects of creep-related failures, where the mechanical strength of a material becomes limited by creep rather than by its elastic limit. The majority of information provided is applicable to metallic materials, and only general information regarding creep-related failures of polymeric materials is given. The article also reviews various factors related to creep behavior and associated failures of materials used in high-temperature applications. The complex effects of creep-fatigue interaction, microstructural changes during classical creep, and nondestructive creep damage assessment of metallic materials are also discussed. The article describes the fracture characteristics of stress rupture. Information on various metallurgical instabilities is also provided. The article presents a description of thermal-fatigue cracks, as distinguished from creep-rupture cracks.

Erosion is the progressive loss of original material from a solid surface due to mechanical interaction between that surface and a fluid, a multicomponent fluid, an impinging liquid, or impinging solid particles. The detrimental effects of erosion have caused problems in a number of industries. This article describes the processes involved in erosion of ductile materials, brittle materials, and elastomers. Some examples of erosive wear failures are given on abrasive erosion, liquid impingement erosion, cavitation, and erosion-corrosion. In addition, the article provides information on the selection of materials for applications in which erosive wear failures can occur.

Erosion of a solid surface can be brought about by liquid droplet impingement (LDI), which is defined as "progressive loss of original material from a solid surface due to continued exposure to erosion by liquid droplets." In this article, the emphasis is placed on the damage mechanism of LDI erosion under the influence of a liquid film and surface roughness and on the prediction of LDI erosion. The fundamentals of LDI and processes involved in initiation of erosion are also discussed.

This article describes the methods for removing metallic contaminants, tarnish, and scale resulting from hot-working or heat-treating operations on nickel-, cobalt-, and iron-base heat-resistant alloys. It provides a brief description of applicable finishing and coating processes, including polishing, electroplating, ceramic coatings, diffusion coatings, and shot-peening. The article presents numerous examples that identify cleaning and finishing problems and the procedures used to solve them.

Thermomechanical fatigue (TMF) is the general term given to the material damage accumulation process that occurs with simultaneous changes in temperature and mechanical loading. TMF may couple cyclic inelastic deformation accumulation, temperature-assisted diffusion within the material, temperature-assisted grain-boundary evolution, and temperature-driven surface oxidation, among other things. This article discusses some of the major aspects and challenges of dealing with TMF life prediction. It describes the damage mechanisms of TMF and covers various experimental techniques to promote TMF damage mechanisms and elucidate mechanism coupling interactions. In addition, life modeling in TMF conditions and a practical application of TMF life prediction are presented.

Fusible alloys, eutectic and noneutectic, include a group of binary, ternary, quaternary, and quinary alloys containing bismuth, lead, tin, cadmium, and indium that melt at relatively low temperatures. This article describes the composition and mechanical properties of these alloys and lists the values of their composition and melting temperatures.

The principal task of a failure analyst during a physical-cause investigation is to identify the sequence of events involved in the failure. Technical skills and tools are required for such identification, but the analyst also needs a mental organizational framework that helps evaluate the significance of observations. This article discusses the processes involved in the characterization and identification of damage and damage mechanisms. It describes the relationships between damage causes, mechanisms, and modes with examples. In addition, some of the more prevalent and encompassing characterization approaches and categorization methods of damage mechanism are also covered.

Physical vapor deposition (PVD) coatings are harder than any metal and are used in applications that cannot tolerate even microscopic wear losses. This article describes the three most common PVD processes: thermal evaporation, sputtering, and ion plating. It also discusses ion implantation in the context of research and development applications.

Nickel-base alloy castings are widely used in corrosive-media and high-temperature applications. This article begins with a discussion on the compositions of corrosion-resistant nickel-base casting alloys and heat-resistant nickel-base casting alloys. It describes the effects of aluminum and titanium on the structure and properties of nickel-base alloys. The article provides information on the melting, foundry, and pouring practices for nickel-base alloys. It describes the welding and heat treatment of the nickel-base casting alloys. The article concludes with information on the numerous applications of cast heat-resistant nickel-base alloys.

The commonly used nondestructive testing of cast products include liquid penetrant inspection, radiographic inspection, fluoroscopic inspection and automated defect recognition, ultrasonic inspection, eddy current inspection, process-controlled resonant testing (PCRT), leak test, and electrical conductivity measurements. This article summarizes the application of these nondestructive tests to castings. It also tabulates a partial list of automotive part types and materials amenable to PCRT and lists the potential limitations to the use of PCRT.

This article reviews nondestructive testing (NDT) and inspection techniques, namely liquid penetrant, magnetic particle, ultrasonics, X-ray, eddy current, visual and radiography that are commonly used to detect and evaluate flaws or leaks in an engineering system. This article compares the merits and limitations of these techniques and describes the various uses of NDT, including leak detection, metrology, structure or microstructure characterization, stress-strain response determination, and rapid identification of metals and alloys.