The gas-tungsten arc welding (GTAW) process is performed using a welding arc between a nonconsumable tungsten-base electrode and the workpieces to be joined. The arc discharge requires a flow of electrons from the cathode through the arc column to the anode. This article discusses two cases of electron discharge at the cathode: thermionic emission and nonthermionic emission, also called cold cathode, or field emission. It schematically illustrates relative heat transfer contributions to workpiece in the GTAW process. The article provides information on the effects of cathode tip shape and shielding gas composition in the GTAW process.

This article provides the basic physics of the two most widely used arc welding processes: gas tungsten arc welding and gas metal arc welding. It describes the various control parameters of these processes such as arc length control, voltage control, heat input control, and metal-transfer control.

This article describes the applications, process capabilities, and limitations and advantages of electrostream and capillary drilling. It describes equipment and tooling used for electrostream and capillary drilling. These include electrostream and capillary drilling machines, power supplies, electrolyte system, part holding fixtures, cathode holders, and cathode tubes. Key process parameters for electrostream and capillary drilling are also discussed.

Shaped tube electrolytic machining (STEM) is a modified electrochemical machining (ECM) process that uses an acid electrolyte so that the removed metal goes into the solution instead of forming a precipitate. This article lists some specific machining applications of the STEM process, including turbine blade cooling holes, turbine vane cooling holes, turbine disk cooling passages, oil passages, and fuel nozzles. It describes the limitations and advantages of the STEM process. The article discusses the various tool parts of the STEM system, including the holding fixture, guide for cathodes, cathodes, and cathode holder/manifold. The article concludes with information on the process parameters of the STEM system.

Plasma melting is a material-processing technique in which the heat of thermal plasma is used to melt a material. This article discusses two typical design principles of plasma torches in the transferred mode: the tungsten tip design and the hollow copper electrode design. It describes the sources of atmospheric contamination in plasma melting furnaces and their control measures. The equipment used in plasma melting furnaces are also discussed. The article provides a detailed discussion on various plasma melting processes, such as plasma consolidation, plasma arc remelting, plasma cold hearth melting, and plasma casting.

Specific machining processes that employ electrochemical machining technology include deburring and deep-hole drilling. This article describes the principle and applications of electrochemical deburring as well as the machine tools used in the process. The system, process capabilities, and applications of electrochemical deep-hole drilling are also discussed. The article also reviews the pulse electrochemical machining.

Stress-corrosion cracking (SCC) is a phenomenon in which time-dependent crack growth occurs when the necessary electrochemical, mechanical, and metallurgical conditions exist. This article provides an overview of the environmental phenomenon, mechanisms, and controlling parameters of SCC. It describes the phenomenological and mechanistic aspects of the initiation and propagation of SCC. The article includes a phenomenological description of crack initiation and propagation that describes well-established experimental evidence and observations of stress corrosion. Discussions on mechanisms describe the physical process involved in crack initiation and propagation. The article also includes information on dissolution models and mechanical fracture models.

Plasma-metal inert gas (MIG) welding can be defined as a combination of plasma arc welding (PAW) and gas-metal arc welding (GMAW) within a single torch, where a filler wire is fed through the plasma nozzle orifice. This article describes the principles of operation and operating modes of plasma-MIG welding. It discusses the advantages and disadvantages of the plasma-MIG process. The article describes the components, including power sources and welding torches, of equipment used for the plasma-MIG process. It provides information on inspection and weld quality control and troubleshooting techniques. The article concludes with a discussion on the applications of the plasma-MIG process.

This article discusses the principles of corrosion and the basis of the various prevention measures that can be taken for different corrosion modes. It describes aqueous corrosion phenomena in terms of the electrochemical reactions that occur at the metal-environment interface. The article explains the specific forms of corrosion, including general corrosion, localized attack, and environmentally assisted cracking. It provides a discussion on the engineering aspects of design that can, without due care and attention, precipitate unexpected premature failure. The article reviews ways to improve corrosion awareness and prevent corrosion/degradation. It describes a life prediction method with an example of environmental degradation in light-water nuclear reactors. The article concludes with a discussion on the validation of life-prediction algorithms and their applications.

Plasma gas metal arc welding (GMAW) is a process that can be defined as a combination of plasma arc welding (PAW) and GMAW within a single torch, where a filler wire is fed through the plasma nozzle orifice. Although originally referred to as plasma-MIG welding, the preferred term is plasma-GMAW. This article provides a detailed discussion on the operating procedures, advantages, disadvantages, and applications of GMAW and describes the equipment used in the plasma-GMAW.

Corrosion fatigue refers to the phenomenon of cracking in materials under the combined actions of fatigue loading and a corrosive environment. This article focuses on the various mechanisms of corrosion fatigue, namely, hydrogen-assisted cracking, anodic dissolution, and surface energy reduction. It discusses the variables affecting corrosion fatigue. The effect of fatigue load frequency, environment, grain size, stress ratio, waveform, and temperature fatigue crack growth are also discussed.

This article discusses various concepts of micro x-ray diffraction (XRD) used for the examination of materials in situ. The discussion covers the principles, equipment used, sample preparation procedure, considerations for calibrating a detector, steps for performing data analysis, and applications and interpretation of micro-XRD.

Electrochemical machining (ECM) is the controlled removal of metal by anodic dissolution in an electrolytic cell in which the workpiece is the anode and the tool is the cathode. This article begins with a description of the ECM system and then discusses the primary variables that affect current density and the material removal rate in the ECM process. It reviews the various characteristics of electrolytes and considers tool material and design. It also provides an overview of the properties of the workpiece and defines the surface finish and accuracy of an electrochemically machined sample. The variety of work done by electrochemical machining is also exemplified in the article.

This article discusses the operating principles, types, and applications of shearing and slitting of different forms of steel, including plates, flat sheets, bars, coiled sheet and strips. In addition, it provides a detailed account of the cutting methods such as oxyfuel gas cutting, plasma arc cutting, oxygen arc cutting, laser beam cutting, and air carbon arc cutting and gouging, describing their process capabilities, equipment used, operating principles and parameters, and factors affecting their efficiency.

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.

Fracture surfaces are fragile and subject to mechanical and environmental damage that can destroy microstructural features. This article discusses the importance of care and handling of fractures and the factors that need to be considered during the preliminary visual examination. It describes the procedures for sectioning a fracture and opening secondary cracks as well as the effect of nondestructive inspection on subsequent evaluation. The article provides information on the most common techniques for cleaning fracture surfaces. These techniques are dry air blast cleaning, replica stripping, organic-solvent cleaning, water-base detergent cleaning, cathodic cleaning, and chemical-etch cleaning.

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.

The gas tungsten arc welding (GTAW) process derives the heat for welding from an electric arc established between a tungsten electrode and the part to be welded. This article provides a discussion on the basic operation principles, advantages, disadvantages, limitations, and applications of the process. It describes the equipment used for GTAW, namely, power supplies, torch construction and electrodes, shielding gases, and filler metals as well as the GTAW welding procedures. The article concludes with a review of the safety precautions to avoid possible hazards during the GTAW process: electrical shock, fumes and gases, arc radiation, and fire and explosion.

Arc welding is one of several fusion processes for joining metals. This article introduces the fundamentals of arc welding and provides a summary of its history and early discoveries.

Stress-corrosion cracking (SCC) occurs under service conditions, which can result, often without any prior warning, in catastrophic failure. Hydrogen embrittlement is distinguished from stress-corrosion cracking generally by the interactions of the specimens with applied currents. To determine the susceptibility of alloys to SCC and hydrogen embrittlement, several types of testing are available. This article describes the constant extension testing, constant load testing, constant strain-rate testing for smooth specimens and precracked or notched specimens of SCC. It provides information on the cantilever beam test, wedge-opening load test, contoured double-cantilever beam test, three-point and four-point bend tests, rising step-load test, disk-pressure test, slow strain-rate tensile test, and potentiostatic slow strain-rate tensile test for hydrogen embrittlement.