This article discusses the properties, behaviors, and uses of cobalt and its alloys. It explains how cobalt alloys are categorized and describes the commercial designations and grades that are available. It also provides composition information and explains how alloying elements and carbides affect toughness, hardness, ductility, and strength as well as resistance to heat, corrosion, and wear.

Superalloys are nickel, iron-nickel, and cobalt-base alloys designed for high-temperature applications, generally above 540 deg C. This chapter covers the metallurgy, composition, and properties of cast and wrought superalloys. It provides information on melting, heat treating, and secondary fabrication processes. It also covers coating technology, including aluminide diffusion and overlay coatings, and addresses the advantages and disadvantages of superalloys in various applications.

Nickel and nickel alloys have an excellent combination of corrosion, oxidation, and heat resistance, combined with good mechanical properties. Nickel alloys can be divided into alloys that combine corrosion and heat resistance, superalloys for high-temperature applications, and special nickel alloys. Corrosion- and heat-resistant nickel alloys include commercially pure and low-alloy nickels, nickel-copper alloys, nickel-molybdenum and nickel-silicon alloys, nickel-chromium-iron alloys, nickel-chromium-molybdenum alloys, and nickel-chromium-iron-molybdenum-copper alloys. Special nickel alloys include electrical-resistance alloys, low-expansion alloys, magnetically soft alloys, and shape memory alloys. This chapter discusses the metallurgy, nominal composition, properties, applications, advantages, and disadvantages of these alloys. It also provides information on cobalt wear-resistant alloys and cobalt corrosion-resistant alloys.

This chapter describes the metallurgy of superalloys and the extent to which it can be controlled. It discusses the alloying elements, crystal structures, and processing sequences associated with more than a dozen phases that largely determine the characteristics of superalloys, including their properties, behaviors, and microstructure. It examines the role of more than 20 alloying elements, including phosphorus (promotes carbide precipitation), boron (improves creep properties), lanthanum (increases hot corrosion resistance), and carbon and tungsten which serve as matrix stabilizers. It explains how precipitates provide strength by impeding deformation under load. It also discusses the factors that influence grain size, shape, and orientation and how they can be controlled to optimize mechanical and physical properties.

This article discusses the composition, structure, and properties of iron-nickel-, nickel-, and cobalt-base superalloys and the effect of major alloying and trace elements. It describes the primary and secondary roles of each alloying element, the amounts typically used, and the corresponding effect on properties and microstructure. It also covers mechanical alloying and weldability and includes nominal composition data on many wrought and cast superalloys.

The qualities that make superalloys excellent engineering materials also make them difficult to machine. This chapter discusses the challenges involved in machining superalloys and the factors that determine machinability. It addresses material removal rates, cutting tool materials, tool life, and practical issues such as set up time, tool changes, and production scheduling. It describes several machining processes, including turning, boring, planing, trepanning, shaping, broaching, drilling, tapping, thread milling, and grinding. It also provides information on toolholders, fixturing, cutting and grinding fluids, and tooling modifications.

Nonferrous metals are of commercial interest both as engineering materials and as alloying agents. This chapter addresses both roles, discussing the properties, processing characteristics, and applications of several categories of nonferrous metals, including light metals, corrosion-resistance alloys, superalloys, refractory metals, low-melting-point metals, reactive metals, precious metals, rare earth metals, and metalloids or semimetals. It also provides a brief summary on special-purpose materials, including uranium, vanadium, magnetic alloys, and thermocouple materials.

This chapter provides a brief overview of nickel-iron-base, cobalt-base, and nickel-base superalloys, discussing their basic metallurgy and defining characteristics.

This chapter examines the effect of heat treating and other processes on the microstructure-property relationships that occur in superalloys. It discusses precipitation and grain-boundary hardening and how they influence the phases, structures, and properties of various alloys. It explains how the delta phase, which is used to control grain size in IN-718, improves strength and prevents stress-rupture embrittlement. It describes heat treatments for different product forms, discusses the effect of tramp elements on grain-boundary ductility, and explains how section size and test location influence measured properties. It also provides information and data on the physical and mechanical properties of superalloys, particularly tensile strength, creep-rupture, fatigue, and fracture, and discusses related factors such as directionality, porosity, orientation, elongation, and the effect of coating and welding processes.

This appendix includes selected references on topics related to the production and application of superalloys, including properties and microstructure; melting/ingot breakdown; forging/powder metallurgy; machining, heat treating, joining, refurbishment/repair; investment casting; coatings/corrosion; and modeling.

This chapter discusses the application of investment casting to nickel- and cobalt-base superalloys. It describes the production of polycrystalline and single crystal castings, the materials normally used, and the part dimensions and tolerances typically achieved. It explains how patterns, molds, and shells are produced, discusses the practice of directional solidification, and examines an assortment of turbine components cast from nickel- and cobalt-base alloys. The chapter also addresses casting problems such as inclusions, porosity, distortion, core shift, and leaching and explains how to avoid them.

The microstructure of superalloys is highly complex, with a large number of dispersed intermetallics and other phases that modify alloy behavior through their composition, morphology, and distribution. This chapter provides an overview of the most notable phases, including the matrix phase and geometrically and topologically close-packed phases, and describes how superalloy microstructure can be modified via heat treatments and directional solidification. It also discusses the role of carbides, borides, oxides, and nitrides and the detrimental effects of sulfocarbides.

This article discusses the compositions, structures, and properties of the most common grades of soft magnetic metals and permanent magnet alloys. It explains how alloying additions and impurities affect the magnetic properties of these materials, which include commercially pure and phosphorus irons, low-carbon and silicon steels, ferritic stainless steels, and nickel-iron and iron-cobalt alloys.

This chapter discusses the failure of superalloy components in high-temperature applications where they are subject to the effects of microstructural changes, melting, and corrosion. It explains how overheating can deplete alloying elements and alter the composition and distribution of phases, and how these processes contribute to microstructural changes as a function of time, temperature, and applied stress. It also describes several failure examples and discusses related issues, including damage recovery, refurbishment, and repair.

This chapter covers the tribological properties of stainless steel and other corrosion-resistant alloys. It describes the metallurgy and microstructure of the basic types of stainless steel and their suitability for friction and wear applications and in environments where they are subjected to liquid, droplet, and solid particle erosion. It also discusses the tribology of nickel- and cobalt-base alloys as well as titanium, zinc, tin, aluminum, magnesium, beryllium, graphite, and different types of wood.

This article discusses the general purpose of alloying and identifies some of the material properties and behaviors that can be improved by adding various elements to the base metal. It explains how alloying can make metals stronger and more resistant to corrosion and wear as well as easier to cast, weld, form, and machine. It also discusses some of the alloying techniques that have been developed to address problems stemming from dissimilarities between the base metal and alloying or inoculate material.

This chapter discusses the progress that has been made in the development of superalloy operating temperatures, properties, and performance. It also provides forward-looking projections based on advances in process modeling, alloying, and production techniques.

This article examines the role of alloying in the production and use of nickel and its alloys. It explains how nickel-base alloys are categorized and lists the most common grades along with their compositional ranges and corresponding UNS numbers. It describes the role of nearly 20 alloying elements and how they influence strength, ductility, hardness, and corrosion resistance. It also addresses processing issues, explaining how alloying and intermetallic phases affect forming, welding, and machining operations.