This article provides information on thermal spray coating features, which combine to determine the properties of a coating. These include the lamellar or layered splat structure, entrapped unmelted or resolidified particles, pores, oxide inclusions, grains, phases, cracks, and bond interfaces. The article describes the sources of porosity and the factors that control the final coating porosity levels. The article also lists the materials most suitable for thermal spraying processes.

Materials resulting from thermal spray processes are often different from their wrought, forged, and cast counterparts. Assessing the usefulness of thermal spray coatings requires understanding, developing, and using appropriate testing and characterization methods that are generally borrowed from other materials science disciplines. This article focuses on commonly used testing and characterization methods: metallography, image analysis, hardness, tensile adhesion testing, corrosion testing, x-ray diffraction, non-destructive testing, and powder characterization. It provides information on how the materials themselves respond to the various test methods. The article focuses on the test methods themselves, including those test parameters that can be varied and the influence of each on the results obtained.

This article describes the specific features and mechanisms of oxidation in thermal spray coatings. It discusses the two forms of hot corrosion in sulfur-containing combustion, namely high-temperature hot corrosion and low-temperature hot corrosion. The article reviews the behavior of corrosion-resistant coatings in boilers. The effects of high-temperature corrosion in waste incinerators are detailed. The article also examines the effects of erosion-corrosion in fluidized bed combustion boilers.

This article reviews how process variations influence the characteristics of thermal spray coatings. It describes various specimen preparation techniques, which allow accurate microstructural analysis. These techniques include sectioning, cleaning, mounting, planar grinding, fine grinding, rough polishing, and etching. The article provides information on the problems associated with specimen preparation. It concludes with a discussion on the various methods of analysis for thermal spray coatings.

Thermal spray processes involve complete or partial melting of a feedstock material in a high-temperature flame, and propelling and depositing the material as a coating on a substrate. This article describes the properties of sprayed electronic materials, including dielectrics, conductors, and resistors, and discusses their implications and associated limitations for device applications and potential remedial measures. The article presents specific examples of electrical/electronic device applications, including electromagnetic interference/radio-frequency interference shielding, planar microwave devices, waveguide devices, sensing devices, solid oxide fuel cells, heating elements, electrodes for capacitors and other electrochemical devices.

Rapid solidification is a tool for modifying the microstructure of alloys that are obtained by ordinary casting. This article describes the fundamentals of the four microstructural changes, namely, microsegregation, identity of the primary phase, identity of the secondary phase, and the formation of noncrystalline phases. It considers three factors to understand the fundamentals of these changes: heat flow, thermodynamic constraints/conditions at the liquid-solid interfaces, and diffusional kinetics/microsegregation. These factors are described in detail.

This article discusses three types of powder-feeder systems that are commonly used throughout the thermal spray (TS) industry: gravity-based devices, rotating wheel devices, and fluidized-bed systems. It provides information on the various mechanical methods for producing powders, namely, crushing, milling, attriting, and machining. The article describes two prime methods of agglomeration. One method uses a binder by way of agglutination, while the other relies on a sintering operation. The article discusses the technology and principles of the processes that relate to thermal spraying, and offers an understanding for choosing particular feedstock materials that are classified based on the thermal spray process, material morphology, chemical nature of the material, and applications. Sieving, the most common method of separating powders into their size fractions, is also reviewed. The article also provides information on the topical areas and precautions to be undertaken to protect the operator from safety hazards.

This article provides a brief discussion on the common types of overlayers that can be used on a metal surface to protect it from corrosion. These overlayers include phosphate, chromate, and chromate-free conversion coatings; hot dip galvanizing; cementitious linings; glass and porcelain enamels; electroplating; thermal spray coatings; and rubber linings.

A major effort in the development of thermal spray applications has been the improvement of process reliability and predictability in response to process changes. The ability to model a process is a prerequisite to understanding and controlling it. This article provides an overview of thermal spray process modeling, as it applies to the engineering of new thermal spray equipment and coating development.

Surface treatments are used in a variety of ways to improve the material properties of a component. This article provides information on surface treatments that improve service performance so that the design engineer may consider surface-engineered components as an alternative to more costly materials. It describes solidification surface treatments such as hot dip coatings, weld overlays, and thermal spray coatings. The article discusses deposition surface treatments such as electrochemical plating, chemical vapor deposition, and physical vapor deposition processes. It explains surface hardening and diffusion coatings such as carburizing, nitriding, and carbonitriding. The article also tabulates typical characteristics of carburizing, nitriding, and carbonitriding diffusion treatments.

This article is a compilation of definition of the terms related to thermal spray coating technology.

Metallographic examination is a critical step in the assessment of thermal spray coating characteristics. This article discusses the major steps involved in metallographic examination: sectioning, mounting, grinding, polishing, optical microscopy, and image analysis. It provides a discussion on etching to reveal grain structure. The article also provides recommendations for metallographic examination of some standard coatings.

This article illustrates typical wear and friction issues encountered in gas and steam turbines and their consequences as well as commonly adopted materials solutions. It contains tables that present the summary of wear and friction related issues encountered in steam turbines and gas turbines. The article outlines the differences in the operating conditions and the nature of the components involved in gas and steam turbines. It discusses the constraints and applicable coating solutions for wear and friction issues, and concludes with a broad set of challenges that need to be addressed to improve performance and operability of gas and steam turbines.

Castability is a complex characteristic that depends on both the intrinsic fluid properties of the molten metal and the manner in which the particular alloy solidifies. This article discusses the practical aspects of solidification important to aluminum foundrymen. The primary focus is on the chemical segregation that occurs during freezing, because it determines the castability of the alloy. The article describes the two types of segregation, namely, microsegregation and macrosegregation. It discusses the effect of freezing range on castability of an alloy. The article lists the freezing range of a number of important alloys. It concludes with a discussion on castability of 2xx, 3xx, 4xx, 5xx, and 7xx alloys.

This article reviews the use of thermal spray polymer coatings as a replacement for paints. It discusses the applications of the thermal spray forming process. The article also provides information on the applications of thermal spray in metal processing, textile and plastics, and ceramic and glass manufacturing industries.

Additive manufacturing is a collection of manufacturing processes, each of which builds a part additively based on a digital solid model. The solid model-to-additive manufacturing interface and material deposition are entirely computer-controlled. The traditional additive manufacturing applications have been used for low production runs of parts with complex shapes and geometric features. Additive manufacturing is also used for topology optimization and it impacts the process and supply chain. This article discusses processes, including vat photopolymerization, material jetting, powder bed fusion, directed energy deposition, material extrusion, binder jetting, and sheet lamination.

Martensite is a metastable structure that forms during athermal (nonisothermal) conditions. This article reviews the crystallographic theory, morphologies, orientation relationships, habit plane, and transformation temperature of ferrous martensite microstructures. It examines the stages of the tempering process involved in ferrous martensite. The article also describes the formation of the martensite structure in nonferrous systems. It concludes with a discussion on shape memory alloys.

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.

This article describes the structure of coatings produced by plasma spraying, vapor deposition, and electrodeposition processes. The main techniques used for microstructure assessment are introduced. The relationship between the microstructure and property is also discussed. The experimental techniques for microstructural characterization include metallographic technique, X-ray diffraction, electron, microscopies, and porosimetry.

This article begins with a description of the advantages and disadvantages of thermal spraying. It provides a discussion on the importance of substrate processing prior to coating and the role of undercutting in repair. The article reviews the steps for substrate preparation, namely, cleaning, roughening, masking, and preheating. Information on the equipment and process variables of dry abrasive grit blasting are also provided. The article describes the roles of spray stream and the spray pattern for all thermal spray processes. It discusses the defects arising from poor temperature control and from the variables influencing the manipulation of the spray torch. The article concludes with helpful information on calculating the process efficiency of thermal spraying.