Boriding is a thermochemical diffusion-based surface-hardening process that can be applied to a wide variety of ferrous, nonferrous, and cermet materials. It is performed on metal components as a solution for extending the life of metal parts that wear out too quickly in applications involving severe wear. This article presents a variety of methods and media used for boriding of ferrous materials, and explains their advantages, limitations, and applications. These methods include pack cementation boriding, gas boriding, plasma boriding, electroless salt bath boriding, electrolytic salt bath boriding, and fluidized-bed boriding. The article briefly describes the chemical vapor deposition process, which has emerged to be dominant among metal-boride deposition processes.

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 provides a brief introduction to abrasive wear-resistant coating materials that contain a large amount of hard phases, such as borides, carbides, or carboborides. It describes some of the commonly used methods of producing thick wear-resistant coatings. The article also provides information on metal-matrix composites and cemented carbides. The three base-alloying concepts, including cobalt-, iron-, and nickel-base alloys used for wear-protection applications, are also described. The article compares the tribomechanical properties of the materials in a qualitative manner, thus allowing a rough materials selection for practitioners. It presents a brief discussion on hot isostatic pressing (HIP) cladding, sinter cladding, and manufacturing of thick wear-resistant coatings by extrusion or ring rolling. The article also discusses the processing sequence of thick wear-resistant coatings, namely, compound casting, deposition welding, and thermal spraying.

Tool steels are carbon, alloy, and high-speed steels that can be hardened and tempered to high hardness and strength values. This article discusses the classifications of commonly used tool steels: water-hardening tool steels, shock-resisting tool steels, cold-work tool steels, and hot-work tool steels. It describes four basic mechanisms of tool steel wear: abrasion, adhesion, corrosion, and contact fatigue wear. The article describes the factors to be considered in the selection of lubrication systems for tool steel applications. It also discusses the surface treatments for tool steels: carburizing, nitriding, ion or plasma nitriding, oxidation, boriding, plating, chemical vapor deposition, and physical vapor deposition. The article describes the properties of high-speed tool steels. It summarizes the important attributes required of dies and the properties of the various materials that make them suitable for particular applications. The article concludes by providing information on abrasive wear and grindability of powder metallurgy steels.

This article describes the surface modification treatments used to modify the tribological properties of titanium alloys. These include physical vapor deposition and thermochemical conversion treatments. The physical vapor deposition includes ion implantation, sputtering, evaporation, and ion plating surface modification treatments. The thermochemical conversion surface treatments include nitriding, carburizing, boriding, and solid lubrication.

Passivation; pickling, that is, acid descaling; electropolishing; and mechanical cleaning are important surface treatments for the successful performance of stainless steel used for piping, pressure vessels, tanks, and machined parts in a wide variety of applications. This article provides an overview of the various types of stainless steels and describes the commonly used cleaning methods, namely, alkaline cleaning, emulsion cleaning, solvent cleaning, vapor degreasing, ultrasonic cleaning, and acid cleaning. Finishing operations of stainless steels, such as grinding, polishing, and buffing, are reviewed. The article also explains the procedures of electrocleaning, electropolishing, electroplating, painting, surface blackening, coloring, terne coatings, and thermal spraying. It includes useful information on the surface modification of stainless steels, namely, ion implantation and laser surface processing. Surface hardening techniques, namely, nitriding, carburizing, boriding, and flame hardening, performed to improve the resistance of stainless steel alloys are also reviewed.

This article examines the high-temperature oxidation of silica-forming ceramics under constant temperature and cyclic conditions. The effects of water vapor, impurities, and molten salts are discussed. The article describes the oxidation and corrosion of silica-forming composites, oxide ceramics, non-silica forming nitrides, carbides, and borides. The performance of environmental barrier coatings by material type is also discussed. The article also explains the effects of oxidation and corrosion on the mechanical properties of ceramic-matrix composites. It concludes with information on high-temperature applications, wear properties, and the microscopic analyses of advanced ceramics.

Coatings and other surface modifications are used for a variety of functional, economic, and aesthetic purposes. Two major applications of thermal spray coatings are for wear resistance and corrosion resistance. This article discusses thermal (surface hardening) and thermochemical (carburizing, nitriding, and boriding) surface modifications, electrochemical treatments (electroplating, and anodizing), chemical treatments (electroless plating, phosphating, and hot dip coating), hardfacing, and thermal spray processes. It provides information on chemical and physical vapor deposition techniques such as conventional CVD, laser-assisted CVD, cathodic arc deposition, molecular beam epitaxy, ion plating, and sputtering.

Ceramic-metal composites, or cermets, combine the heat and wear resistance of ceramics with the formability of metals, filling an application niche that includes cutting tools, brake pads, heat shields, and turbine components. This article examines a wide range of cermets, including oxide cermets, carbide and carbonitride cermets, boride cermets, and other refractory types. It describes the powder metallurgy process by which cermets are produced, examining each step from powder preparation to post treatment. It discusses forming and compacting, injection molding, extrusion, rolling, pressing, slip casting, and sintering. It also discusses fundamental concepts such as chemical bonding, chemical composition, microstructure, and the development of physical and mechanical properties.

This article discusses selected highlights of thermodynamic relationships during solidification and nucleation kinetics behavior in connection with the basis of nucleation treatments, such as grain refinement and inoculation, to provide a summary of nucleation phenomena during casting. The article describes nucleation phenomenon such as homogeneous nucleation and heterogeneous nucleation. It examines various grain refinement models, such as the carbide-boride model, the free growth model, and the constitutional undercooling model. The article concludes with information on the thermal analysis techniques for assessing grain-refining characteristics during master alloy processing.

This article provides crystallographic and engineering data for single oxide ceramics, zirconia, silicates, mullite, spinels, perovskites, borides, carbides, silicon carbide, boron carbide, tungsten carbide, silicon-nitride ceramics, diamond, and graphite. It includes data on crystal structure, density, mechanical properties, physical properties, electrical properties, thermal properties, and magnetic properties.

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.

Chemical vapor deposition (CVD) involves the formation of a coating by the reaction of the coating substance with the substrate. Serving as an introduction to CVD, the article provides information on metals, ceramics, and diamond films formed by the CVD process. It further discusses the characteristics of different pack cementation processes, including aluminizing, siliconizing, chromizing, boronizing, and multicomponent coating.

Chemical vapor deposition (CVD) involves the formation of a coating by the reaction of the coating substance with the substrate. Serving as an introduction to CVD, the article provides information on metals, ceramics, and diamond films formed by the CVD process. It further discusses the characteristics of different pack cementation processes, including aluminizing, siliconizing, chromizing, boronizing, and multicomponent coating.

This article discusses the composition, properties and applications of bearing steels. It focuses on the typical wear modes that rolling-element bearings experience: contact fatigue wear, abrasive wear, adhesive wear, and corrosive wear. The article provides information on reliability factor and ABMA and ISO environmental factors.

Grain refinement in aluminum casting alloys tends to reduce the amount of porosity and the size of the pores and to improve mechanical properties, especially fatigue strength. This article provides information on measurement of grain size in alloys and describes the mechanisms of grain refinement in aluminum casting alloys. It reviews the use of boron and titanium as a grain refiner for aluminum casting alloys. The article discusses the best practices for grain refinement in various aluminum casting alloys. These include aluminum-silicon casting alloys, aluminum-silicon-copper casting alloys, aluminum-silicon-copper casting alloys, aluminum-zinc-magnesium casting alloys, and aluminum-magnesium casting alloys. The article also examines the benefits of grain refinement in aluminum casting alloys.

This article describes die wear and failure mechanisms, including thermal fatigue, abrasive wear, and plastic deformation. It summarizes the important attributes required for dies and the properties of the various die materials that make them suitable for particular applications. Recommendations on the selection of the materials for hot forging, hot extrusion, cold heading, and cold extrusion are presented. The article discusses the methods of characterizing abrasive wear and factors affecting abrasive wear. It discusses various die coatings and surface treatments used to extend the lives of dies: alloying surface treatments, micropeening, and electroplating.

This article describes the development of heat-resistant titanium-base alloys and their classification into several microstructure categories based on their strengthening mechanisms. It explains the phase transformation in titanium-aluminum-base alloys and two peritectic reactions that take place in the titanium-aluminum system. The article also describes two approaches for controlling the orientation of the high-temperature alpha phase to achieve the required lamellar orientation by directional solidification in order to improve the strength and ductility of titanium-aluminum alloys. One approach is by seeding the alpha phase in the alloys, and the other is without seeding, by controlling the solidification path of alloys through appropriate alloying. The article discusses the grain refinement technique used to improve the ductility of cast titanium-aluminum alloys to a level of above 1" at room temperature and reasonable room temperature ductility in the as-cast condition. Finally, it provides information on the microstructures produced through various near-net shape manufacturing processes.

Carbon-carbon is a unique composite material in which a nonstructural carbonaceous matrix is reinforced by carbon fibers to create a heat-resistant structural material that finds application in the aerospace and defense industries. This article provides a detailed account of the fundamentals of protecting carbon-carbon composites and explains the various coating deposition techniques, namely, pack cementation, chemical vapor deposition, and slurry coatings. It includes information on the practical limitations of coatings for the carbon-carbon composites.

Surface hardening improves the wear resistance of steel parts. This article focuses exclusively on the methods that involve surface and subsurface modification without any intentional buildup or increase in part dimensions. These include diffusion methods, such as carburizing, nitriding, carbonitriding, and austenitic and ferritic nitrocarburizing, as well as selective-hardening methods, such as laser transformation hardening, electron beam hardening, ion implantation, selective carburizing, and surface hardening with arc lamps. The article also discusses the factors affecting the choice of these surface-hardening methods.