Hardfacing is a form of surfacing that is applied for the purpose of reducing wear, abrasion, impact, erosion, galling, or cavitation. This article describes the deposition of hardfacing alloys by oxyfuel welding, various arc welding methods, laser welding, and thermal spray processes. It discusses the categories of hardfacing alloy, such as build-up alloys, metal-to-metal wear alloys, metal-to-earth abrasion alloys, tungsten carbides, and nonferrous alloys. A summary of the selection guide for hardfacing alloys is presented in a table. The article describes the procedures for stainless steel weld cladding and the factors influencing joint integrity in dissimilar metal joining. It concludes with a discussion on joining carbon and low-alloy steels to various dissimilar materials (both ferrous and nonferrous) by arc welding.

Dissimilar metal welding applications require careful control over the welding parameters and corresponding dilution level in order to produce welds with proper microstructure and properties for the intended service. This article reviews the relation between the dilution and bulk fusion-zone compositions and describes the effect of fusion welding parameters on dilution. It also provides typical examples of the microstructure and property control in dissimilar weld applications.

The process of making assemblies of solid-solution and precipitation hardening groups of alloys and superalloys often requires welding of dissimilar metals, welding of diffusion-bonded materials, and sometimes weld overlay cladding and even thermal spraying that in turn requires special knowledge and treatments developed specifically for each material. This article emphasizes the special metallurgical welding considerations for welding solid-solution and precipitation hardening nickel alloys, cobalt alloys, and superalloys.

This article provides a review of metallographic procedures and techniques for analyzing the microstructure of fusion welded joints. It discusses sample preparation, the use of backing plates, and common sectioning methods. It identifies the various types of defects that can occur in arc welded metals, organizing them according to the sectioning method by which they are observed. It describes the relationship between weld bead morphology and sectioning direction and its effect on measurement error. The article examines micrographs from stainless steel, aluminum, and titanium alloy joints, highlighting important details such as solidification and solid-state transformation structures and what they reveal about the welding process. Besides arc welding, it also discusses laser and electron beam welding methods, resistance and spot welding, and the welding of dissimilar metals.

This article provides information on the practice considerations for the inertia and direct-drive rotary friction welding processes. It presents the tooling and welding parameter designs of these processes. The article discusses the welding of different material family classes to provide a baseline for initial development of a welding parameter set. Common material family classes, including steels, nonferrous metals, and dissimilar metals, are discussed.

Ultrasonic additive manufacturing (UAM) is a solid-state hybrid manufacturing technique that leverages the principles of ultrasonic welding, mechanized tape layering, and computer numerical control (CNC) machining operations to create three-dimensional metal parts. This article begins with a discussion on the process fundamentals and process parameters of UAM. It then describes metallurgical aspects in UAM. The article provides a detailed description of a wide range of mechanical characterization techniques of UAM, namely tensile testing, peel testing, and pushpin testing. The article ends with information on sensor embedding.

This article briefly describes the welding of various stainless steels to dissimilar steels. The stainless steels include austenitic stainless steels, ferritic stainless steels, and martensitic stainless steels. The dissimilar steels include carbon and low-alloy steels. In addition, the article provides information on the cladding of austenitic stainless steel to carbon or low-alloy steels.

Diffusion welding involves minimal pressurization, but relatively high temperatures and long periods of time. This article discusses the process variants of diffusion welding: solid-phase and liquid-phase processes. It describes the diffusion welding of carbon and low-alloy steels, high-strength steels, stainless steels, and aluminum-base alloys. The article provides a discussion on dissimilar metal combinations, such as ferrous-to-ferrous combinations, nonferrous-to-nonferrous combinations, ferrous-to-nonferrous combinations, and metal-ceramic joining.

This article describes two methods based on rolling of sheet. The first is roll welding, where two or more sheets or plates are stacked together and then passed through rolls until sufficient deformation has occurred to produce solid-state welds. The other is laser roll welding, which is a hybrid process based on a thin-melting interface for a lap joint of dissimilar-metal sheets using a roller and one-sided laser heating. The article discusses the types, advantages, and applications of roll welding and laser roll welding. It also provides a detailed discussion on the laser roll welding of dissimilar metals.

Ultrasonic welding (USW) is effectively used to join both similar and dissimilar metals with lap-joint welds. This article describes procedure considerations for the ultrasonic welding of specific material types. It reviews difficult-to-weld alloys, such as carbon and low-alloy steels, high-strength steels, and stainless steel, and provides information on the applications of weldable alloys such as aluminum alloys and copper alloys. The article concludes with a discussion on welding of dissimilar metal (nonferrous-to-nonferrous) combinations and its applications.

Explosion welding (EXW) is a solid-state metal-joining process that uses explosive force to create an electron-sharing metallurgical bond between two metal components. This article discusses the process attributes of EXW, including metallurgical attributes, metal combinations, size limitations, configuration limitations, and bond zone morphology. It provides an overview of the common industrial applications and shop welding applications of EXW products. The article reviews different safety standards and regulations, such as noise and vibration abatement and process geometry. It concludes with a section on the EXW process sequence for welding a two-component flat plate product.

This article describes the solid-phase and liquid-phase processes involved in diffusion bonding of metals. It provides a detailed discussion on the diffusion bonding of steels and their alloys, nonferrous alloys, and dissimilar metals. Ceramic-ceramic diffusion welding and a variation on this process in which ceramic powder compacts are simultaneously sintered and bonded are also discussed.

Electron-beam welding (EBW) can produce deep, narrow, and almost parallel-sided welds with low total heat input and relatively narrow heat-affected zones in a wide variety of common and exotic metals. This article discusses the joint configurations and shrinkage stresses encountered in various joint designs for electron-beam welding, as well as special joints and welds including multiple-pass welds, tangent-tube welds, three-piece welds, and multiple-tier welds. It provides a comparison of medium vacuum EBW with high-vacuum EBW. Scanning is a method of checking the run-out between the beam spot and the joint to be welded. The article describes various scanning techniques for welding dissimilar metals and provides information on the application of electron-beam wire-feed process for repairs. It concludes with a discussion on EBW of heat-resistant alloys, refractory metals, aluminum alloys, titanium alloys, copper and copper alloys, magnesium alloys, and beryllium.

Roll welding (ROW) is a process in which two or more sheets or plates are stacked together and then passed through the rolls until sufficient deformation has occurred to produce solid-state welds. This article begins with a process description of two modes of roll welding, including pack rolling. It describes a patented roll welding process for fabrication of heat exchangers. The article presents a table showing the typical properties of common roll welded clad laminates. The relative weldability of selected dissimilar metals and alloys roll welded into clad-laminate form are also tabulated. The article concludes with information on cladding of metals by strip roll welding.

Friction welding (FRW) is a solid-state welding process that uses the compressive force of the workpieces that are rotating or moving relative to one another, producing heat and plastically displacing material from the faying surfaces to create a weld. This article reviews practice considerations for the two most common variations: inertia welding and direct-drive friction welding. Direct-drive friction welding differs from inertia welding, primarily in how the energy is delivered to the joint. The article discusses the parameter calculations for inertia welding and direct-drive friction welding. It provides information on friction welding of carbon steels, stainless steels, aluminum-base alloys, and copper-, nickel-, and cobalt-base materials.

Friction welding (FRW) is a solid-state welding process in which the heat for welding is produced by the relative motion of the two interfaces being joined. This article provides an outline of the mechanisms of friction heating and discusses the two principal FRW methods: direct-drive welding and inertia-drive welding. It summarizes the similar and dissimilar metals that can be joined by FRW and discusses the metallurgical considerations that govern the properties of the resulting weld.