Nickel-base alloys are generally used in harsh environments that demand either corrosion resistance or high-temperature strength. This article first describes the general welding characteristics of nickel-base alloys. It then describes the weldability of solid-solution nickel-base alloys in terms of grain boundary precipitation, grain growth, and hot cracking in the heat-affected zone; fusion zone segregation and porosity; and postweld heat treatments. Next, the article analyzes the welding characteristics of dissimilar and clad materials. This is followed by sections summarizing the various types and general weldability of age-hardened nickel-base alloys. The article then discusses the composition, welding metallurgy, and properties of cast nickel-base superalloys. Finally, it provides information on the welding of dissimilar metals, filler metal selection for welding clad materials and for overlay cladding, service conditions during repair, and welding procedural idiosyncrasies of cobalt-base alloys.

This chapter discusses the metallurgical changes that occur and the improvements that can be achieved in superalloys through solid-solution hardening, precipitation hardening, and dispersion strengthening. It also explains how further improvements can be achieved through the control of grain structure, as in columnar-grained alloys, or by the elimination of grain boundaries as with single-crystal superalloys.

Nickel-base alloys used for low-temperature aqueous corrosion are commonly referred to as corrosion-resistant alloys (CRAs), and nickel alloys used for high-temperature applications are known as heat-resistant alloys, high-temperature alloys, or superalloys. The emphasis in this chapter is on the CRAs and in particular nickel-chromium-molybdenum alloys. The chapter provides a basic understanding of general welding considerations and describes the welding metallurgy of molybdenum-containing CRAs and of nickel-copper, nickel-chromium, and nickel-chromium-iron CRAs. It discusses the corrosion behavior of nickel-molybdenum alloys and nickel-chromium-molybdenum alloys. Information on the phase stability and corrosion behavior of nickel-base alloys is also included.

This chapter examines the structural changes that occur in high-carbon steels during austenitization. It describes the effect of heating time and temperature on the production of austenite and the associated transformation of ferrite and cementite in eutectoid, hypoeutectoid, and hypereutectoid steels. It discusses the factors that influence the kinetics of the process, including carbon diffusion and the morphology of the original structure. It describes the nucleation and growth of austenite grains, the effect of grain size on mechanical properties, and the difference between coarse- and fine-grained steels. The chapter also discusses grain-refinement processes and some of the effects of overheating, including sulfide spheroidization, grain-boundary sulfide precipitation, and grain-boundary liquation.

This chapter describes the effects of metallurgical variables on the corrosion of aluminum alloys. Emphasis is placed on the effect of constituent particles on pitting corrosion of aluminum.

This chapter describes the mechanisms, characteristics, and prevention of intergranular and exfoliation corrosion in various aluminum alloys. It discusses susceptible alloys and recommended tempers and presents several examples of exfoliation in aircraft components. It also explains how the two forms of corrosion are related to stress-corrosion cracking.

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.