Hardfacing refers to the deposition of a specially selected material onto a component in order to reduce wear in service as a preventative measure or return a worn component to its original dimensions as a repair procedure. This article provides information on various hardfacing materials, namely, iron-base overlays, chromium carbide-based overlays, nickel- and cobalt-base alloys, and tungsten carbide-based metal-matrix composite overlays. It discusses the types of hardfacing processes, such as arc welding processes, and laser cladded, oxyacetylene brazing and vacuum brazing processes. The arc welding processes include shielding metal arc welding, gas metal arc welding/flux cored arc welding, gas tungsten arc welding, submerged arc welding, and plasma transferred arc welding. The article also reviews various factors influencing the selection of the appropriate hardfacing for specific applications.

Hardfacing is defined as the application of a wear-resistant material, in depth, to the vulnerable surfaces of a component by a weld overlay or thermal spray process Hardfacing materials include a wide variety of alloys, carbides, and combinations of these materials. Iron-base hardfacing alloys can be divided into pearlitic steels, austenitic (manganese) steels, martensitic steels, high-alloy irons, and austenitic stainless steel. The types of nonferrous hardfacing alloys include cobalt-base/carbide-type alloys, laves phase alloys, nickel-base/boride-type alloys, and bronze type alloys. Hardfacing applications for wear control vary widely, ranging from very severe abrasive wear service, such as rock crushing and pulverizing to applications to minimize metal-to-metal wear. This article discusses the types of hardfacing alloys, namely iron-base alloys, nonferrous alloys, and tungsten carbides, and their applications and advantages.

This article focuses on coatings and overlays adopted for use as wear- and corrosion-resistant materials in oil sand processing. It describes the most common application processes for oil sand coatings and overlays, including welding, high-velocity oxyfuel thermal spray, laser cladding, and vacuum brazing. The article provides information on the selection of overlays and materials such as chromium-carbide-base overlays and tungsten carbide metal-matrix composites.

The corrosion issues in the compressor, combustor and turbine sections of industrial gas turbines used in steam production generally depend on the quality of the fuel, air, and water used in the engine than on the specific industrial application. This article focuses on the forms of corrosion and their preventive measures in the compressor, combustor and turbine sections of a steam turbine. The compressor section mainly suffers from aqueous corrosion; while in case of the combustor and turbine sections, which are made of nickel-base superalloys, high-temperature environmental attack in the form of high-temperature oxidation and hot corrosion are predominant. The effect of high-temperature oxidation and hot corrosion on the mechanical properties of superalloys is also discussed.

This article provides a general overview of physical and mechanical properties, alloy compositions, applications, and product forms of cobalt-base alloys as wear-resistant, corrosion-resistant, and/or heat-resistant materials. The discussion is largely focused on cobalt-base alloys for wear resistance, as this is the single largest application area of cobalt-base alloys.

Rolling is the process of reducing the thickness or changing the cross section of a workpiece by compressive forces applied through a set of rolls. This article emphasizes flat rolling and illustrates basic flat-rolling process used to reduce the thickness of a rectangular cross section. It provides a discussion on hot rolling, cold rolling, and warm rolling, as well as lubrication in rolling. The article reviews the lubrication for iron-base and nickel-base materials, light metals, copper-base alloys, and titanium alloys. It discusses the wear mechanism in rolling: abrasion, adhesion, and fatigue, as well as oxidative and corrosive wear. Surface modification techniques, such as hardening by induction heat treating, weld overlay, thermal spray coating, coating via physical vapor deposition (PVD), and laser surface treatment, are also discussed for improving roll service life.

Boronizing is a case hardening process for metals to improve the wear life and galling resistance of metal surfaces. Boronizing can be carried out using several techniques. This article discusses the powder pack cementation process for carrying out boronizing. It describes the structures of boride layers in ferrous materials and boride-layer structures in nickel-base superalloys. The primary reason for boriding metals is to increase wear resistance against abrasion and erosion. The article reviews the wear resistance and coefficient of friction of boride layers, as well as galling resistance of borided surfaces. It concludes with a discussion on boronizing plus physical vapor deposition (PVD) overlay coating.

This article describes the various specimen preparation procedures for lead, lead alloys, and sleeve bearings, including sectioning, mounting, grinding, polishing, and etching. The microscopic examination and microstructures of lead and lead alloys are discussed. The article also provides information on the microstructures of sleeve bearing materials.

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.

This article discusses the general welding characteristics and metallurgical welding considerations that play an important function during the welding of nickel, nickel-copper, nickel-chromium, and nickel-chromium-iron alloys.

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 describes the corrosion modes in a waste-to-energy boiler. It discusses the corrosion protection and alloy performance with an emphasis on two main areas of the boiler: furnace water walls and super heaters.

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 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.

Cobalt is used as an alloying element in alloys for various applications. This article provides a detailed account of the metallurgy of cobalt-base alloys. It focuses on the compositions, properties, and applications of cobalt-base alloys, which include wear-resistant cobalt alloys, heat-resistant cobalt alloys, and cobalt-base corrosion-resistant alloys. The article also describes the heat treatments such as annealing and aging, for these alloys.

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.

There are various coating techniques in practice to prevent the deterioration of steels. This article focuses on dip, barrier, and chemical conversion coatings and describes hot-dip processes for coating carbon steels with zinc, aluminum, lead-tin, and other alloys. It describes continuous electrodeposition for steel strip and babbitting and discusses phosphate and chromate conversion coatings as well. It also addresses painting, discussing types and selection, surface preparation, and application methods. In addition, the article describes rust-preventive compounds and their application. It also provides information on weld-overlay and thermal spray coating, porcelain enameling, and the preparation of enamel frits for steels. The article closes by describing methods and materials for ceramic coating.

Cast iron can be described as an alloy of predominantly iron, carbon, and silicon. This article discusses the classification of cast irons, such as gray cast iron, white cast iron, malleable cast iron, ductile cast iron, and compacted graphite iron. It reviews the various special techniques, such as groove face grooving, studding, joint design modifications, and peening, for improving the strength of a weld or its fitness for service. The article discusses the need for postweld heat treatment that depends on the condition of the casting, possible distortion during subsequent machining, the desired finish of the machined surfaces, and prior heat treatment. It describes various welding process for welding cast irons, including oxyfuel welding, braze welding, shielded metal arc welding, gas metal arc welding, and gas-tungsten arc welding.

This article addresses the cobalt and cobalt-base alloys most suited for aqueous environments and those suited for high temperatures. The performance of cobalt alloys in aqueous environments encountered in commercial applications is discussed. The article provides information on the environmental cracking resistance of the cobalt alloys. Three welding processes that are used for hardfacing with the high-carbon Co-Cr-W alloys, namely, oxyacetylene, gas tungsten arc, and plasma-transferred arc are also discussed. The article examines the effects of various modes of high-temperature corrosion. It describes the applications and fabrication of cobalt alloys for high-temperature service.

High temperature corrosion may occur in numerous environments and is affected by factors such as temperature, alloy or protective coating composition, time, and gas composition. This article explains a number of potential degradation processes, namely, oxidation, carburization and metal dusting, sulfidation, hot corrosion, chloridation, hydrogen interactions, molten metals, molten salts, and aging reactions including sensitization, stress-corrosion cracking, and corrosion fatigue. It concludes with a discussion on various protective coatings, such as aluminide coatings, overlay coatings, thermal barrier coatings, and ceramic coatings.