Plasma arc welding (PAW) can be defined as a gas-shielded arc welding process where the coalescence of metals is achieved via the heat transferred by an arc that is created between a tungsten electrode and a workpiece. This article focuses on the operating principles and procedures, current and operating modes, advantages, disadvantages, and applications of PAW. It discusses the personnel and equipment requirements, as well as the joints used in the process. The power source, plasma control console, water cooler, welding torch, and gas supply system for the plasma and shielding gases are also reviewed.

Plasma arc welding (PAW) can be defined as a gas-shielded arc welding process where the coalescence of metals is achieved via the heat transferred by an arc that is created between a tungsten electrode and a workpiece. This article discusses the melt-in mode and the keyhole mode of the PAW process, as well as the advantages and disadvantages. It describes the components of a basic PAW system, namely the power source, plasma control console, water cooler, welding torch, and gas supply system for the plasma and shielding gases. The article provides information on the applications of the PAW process and discusses the typical components and joints used. It concludes with information on personnel requirements and safety issues.

Significant expansion of thermal spray technology occurred with the invention of plasma spray, detonation gun, and high-velocity oxyfuel (HVOF) deposition technologies. This article provides a brief history of the major initiating inventions/developments of thermal spray processes. It provides information on feedstock materials developed for specific thermal spray processes.

This article presents the major thermal spray processes and their subsets, presenting each of the commercially significant processes together with some of their important variations. Each process is presented along with the attributes that influence coating structure and performance. The article summarizes the essential equipment components and necessary controls. The various thermal spray processes are conventional flame spray, detonation gun, high-velocity oxyfuel spray, electric arc spray, and plasma arc spray. Other processes, such as cold spray, underwater plasma arc spray, and extended-arc and other high-energy plasma arc spray, are also considered.

This article discusses various control processes carried out in powder feeding, thermal spraying, and gas flow of the thermal spray process to standardize the coating quality. Quality of the entire powder feeding process can be achieved by controlling the processing of feeding equipment as well as the characteristics of the powder being fed. Gas flow control can be achieved by using rotameters, critical orifices, and thermal mass flowmeters, whose ability to provide useful information is defined by their resolution, accuracy, linearity, and repeatability. The commercial thermal spray controls discussed here include the open-loop input-based, open-loop output-based, closed-loop input-based, and closed-loop output-based or adaptive controls. The article discusses the common causes and practical solutions for arc starting problems. It also outlines certain important developments in measuring individual and collective particle velocities, temperature, and trajectories as well as other plume characteristics for the plasma spray process.

The hazards associated with thermal spray deposition processes include ultraviolet and infrared radiation; acoustical noise; and by-product production in the forms of nitrous oxides, ozone, fumes, and dust. The most important consideration in health and safety is to use the engineered controls of hazards. This article provides a brief description of the spray booth, the most commonly used engineering tool to separate the operator from the thermal spray process and confine the associated hazards. It also presents guidelines on the proper and safe handling of industrial gases and ventilation and heat exhaust. The article provides information on the personal protective equipment for eyes and skin from radiation, and ears from noise. It also discusses other potential safety hazards associated with thermal spraying, namely, magnetic fields and infrasound.

Plasma (ion) nitriding is a method of surface hardening using glow-discharge technology to introduce nascent (elemental) nitrogen to the surface of a metal part for subsequent diffusion into the material. This article describes the procedures and applications of plasma nitriding methods of steel. These methods include direct-current plasma nitriding, pulsed-current plasma nitriding, and active-screen plasma nitriding. The article reviews cold-walled and hot-walled furnaces used for plasma nitriding. It provides information on the importance of controlling three process parameters: atmosphere, pressure, and part temperature. The article includes a discussion on the influence of nitrogen concentration on case structure formation on nitrided steel, and explains the significance of microstructure, hardness, and fatigue strength on nitrided case. It also discusses processing, laboratory studies, and applications of nitrocarburizing of steel.

This article discusses the safety issues associated with the design and operation of thermal spray booths and spray box structures and the equipment or systems required for operating thermal spray processes. It describes the design elements necessary to mitigate sound, dust and fume, ultraviolet light, and mechanical hazards. The means selected for safeguarding personnel must be based on a formal risk assessment that meets ANSI/RIA standards. The safeguards include sensing devices, barriers, awareness signals, procedures, and training. It also provides guidelines that are intended to increase the safety awareness and the use of safety practices for gas and liquid piping and electrical equipment within thermal spray installations.

Sintering provides the interparticle bonding that generates the attractive forces needed to hold together the otherwise loose ceramic powder mass. It also improves hardness, strength, transparency, toughness, electrical conductivity, thermal expansion, magnetic saturation, corrosion resistance, and other properties. This article discusses the fundamentals of sintering and its effects on pore structures and particle density. It addresses some of the more common sintering methods, including solid-state, liquid-phase, and gas pressure sintering, and presents alternative processes such as reaction sintering and self-propagating, high-temperature synthesis. It also describes several pressure densification methods, including hot isostatic pressing, gas pressure sintering, molten particle deposition, and sol-gel processing. The article concludes with a section on grain growth that discusses the underlying mechanisms and kinetics and the relationship between grain growth and densification.

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

The scanning electron microscopy (SEM) is one of the most versatile instruments for investigating the microstructure of metallic materials. This article highlights the development of SEM technology and describes the operation of basic systems in an SEM, including the electron optical column, signal detection and display equipment, and vacuum system. It discusses the preparation of samples for observation using an SEM and describes the application of SEM in fractography. If the surface remains unaffected and undamaged by events subsequent to the actual failure, it is often a simple matter to determine the failure mode by the use of an SEM. In cases where the surface is altered after the initial failure, the case may not be so straightforward. The article presents typical examples that illustrate these points. Image dependence on the microscope type and operating parameters is also discussed.

The scanning electron microscope (SEM) is one of the most versatile instruments for investigating the microscopic features of most solid materials. The SEM provides the user with an unparalleled ability to observe and quantify the surface of a sample. This article discusses the development of SEM technology and operating principles of basic systems of SEM. The basic systems covered include the electron optical column, signal detection and display equipment, and the vacuum system. The processes involved in the preparation of samples for observation using an SEM are described, and the application of SEM in fractography is discussed. The article covers the failure mechanisms of ductile failure, brittle failure, mixed-mode failure, and fatigue failure. Lastly, image dependence on microscope type and operating parameters is also discussed.

Oxyfuel gas cutting (OFC) includes a group of cutting processes that use controlled chemical reactions to remove preheated metal by rapid oxidation in a stream of pure oxygen. This article discusses the operation principles and process capabilities of the OFC. It reviews the properties and compositions of fuel types such as acetylene, natural gas, propane, propylene, and methyl-acetylene-propadiene-stabilized gas. The article describes the effects of OFC on base metal, including carbon and low-alloy steels, cast irons, and stainless steels. It provides information on light cutting, medium cutting, heavy cutting, and stack cutting. The article informs that the basic oxyfuel method can be modified to allow gas cutting of metals, such as stainless steel and most nonferrous alloys, that resist continuous oxidation.

This article begins with an overview of the fundamentals of adhesive technology, including functions, limitations, adhesive joint types, and the key factors in the selection of adhesives, including application, type of joint, process limitation, mechanical requirement, and service conditions. It then focuses on the characteristics, types, and properties of the five groups of adhesives, such as structural, hot melt, pressure sensitive, water based, ultraviolet, and electron beam cured adhesives. The article also discusses the functions and applications of adhesive modifiers, including fillers, adhesion promoters, tackifiers, and tougheners. It gives a short note on functions of primers and primerless bonding. Applications of adhesives in automotive, aerospace, electronics, electrical, medical, sports, and construction sectors are also described. Finally, the article describes the steps in adhesive bonding, including storage and handling of adhesives, bonding preparation, adhesive application, tooling, and curing.

This article discusses pressure vessels, piping, and associated pressure-boundary items of the types used in nuclear and conventional power plants, refineries, and chemical-processing plants. It begins by explaining the necessity of conducting a failure analysis, followed by the objectives of a failure analysis. Then, the article discusses the processes involved in failure analysis, including codes and standards. Next, fabrication flaws that can develop into failures of in-service pressure vessels and piping are covered. This is followed by sections discussing in-service mechanical and metallurgical failures, environment-assisted cracking failures, and other damage mechanisms that induce cracking failures. Finally, the article provides information on inspection practices.