This chapter explains how the presence of intermediate phases affects the melting behavior of binary alloys and the transformations that occur under different rates of cooling. It begins by examining the phase diagrams of magnesium-lead and copper-zinc, noting some of the complexities associated with intermediate phases. It then discusses the difference between ordered and disordered phases and how they are accounted for on phase diagrams. It describes how the atoms in a disordered solution may arrange themselves into an ordered array, forming a superlattice in the process of cooling, and goes on to identify the most common superlattice structures and their corresponding alloy phases. It also discusses the factors that limit the formation of superlattices along with the kinetics of spinodal decomposition and its effect on microstructure development.

The microstructure of carbon steel is largely determined by the transformation of austenite to ferrite, cementite, and pearlite. This chapter focuses on the microstructures produced by diffusion-controlled transformations that occur at relatively low cooling rates. It describes the conditions that promote such transformations and, in turn, how they affect the structure of various phases and the rate at which they form. The chapter also discusses the concepts of transformation kinetics, minimum free energy, and nucleation and growth, and provides information on alloying, interphase precipitation, and various types of transformations.

This chapter examines two important strengthening mechanisms, martensitic and bainitic transformations, both of which occur under nonequilibrium cooling conditions. It explains how time-temperature-transformation diagrams are constructed and how they are used to understand and control the formation of martensite and bainite in steel and other alloys. It describes the morphology of both types of structures, the factors that influence their formation, how they respond to tempering processes, and their effect on mechanical properties and behaviors. It also discusses the role of transformation hysteresis in shape memory alloys.

This chapter provides an overview of a computational method, called CALPHAD, used for the study of phase equilibria in multicomponent systems. It describes the thermodynamic models and calculation techniques employed in the software and explains how it applies to complex alloys used in industry. It also provides examples showing how CALPHAD has been used to determine the formability of metallic glass, calculate the dilation of stainless steel during phase transformation, and predict the beta transus and approach curves of commercial titanium alloys.

The practical application of metals and alloys is guided largely by information obtained through the study of their microstructure. This chapter examines a wide range of titanium microstructures, identifying characteristic features and explaining what they reveal about processing, properties, and performance. It includes images of elongated and equiaxed structures, primary alpha, transformed beta, and metastable phases as well as spheroidal and intergranular beta, alpha case, and intermetallic compounds. It also defines important terms and provides step-by-step procedures for preparing titanium for metallographic analysis.

This chapter describes the metallurgy, composition, and properties of steels and other alloys. It provides information on the atomic structure of metals, the nature of alloy phases, and the mechanisms involved in phase transformations, including time-temperature effects and the role of diffusion, nucleation, and growth. It also discusses alloying, heat treating, and defect formation and briefly covers condenser tube materials.

The existence of austenite and ferrite, along with carbon alloying, is fundamental in the heat treatment of steel. In view of the importance of structure and its formation to heat treatment, this chapter describes the various microstructures that form in steels, the various factors that determine the formation of microstructures during heat treatment processing of steel, and some of the characteristic properties of each of the microstructures. The discussion also covers the constitution of iron during heat treatment and the phases of heat-treated steel with elaborated information on iron phase transformation, hysteresis in heating and cooling, ferrite and austenite as two crystal structures of solid iron, and the diffusion coefficient of carbon.

When a metal is alloyed with another metal, either substitutional or interstitial solid solutions are usually formed. This chapter discusses the general characteristics of these solutions and the effects of several alloying elements on the yield strength of pure metals. It presents four rules that give a qualitative estimate of the ability of two metals to form substitutional solid solutions: relative size factor, chemical affinity factor, relative valency factor, and lattice type factor. The chapter provides information on alloys that form an ordered structure during heating. It describes the intermediate phases that are formed during solidification between the two extremes of substitutional solid solution on the one hand and intermetallic compound on the other. The chapter concludes with a section on strain aging in low-carbon steels that allows the interstitial atoms to diffuse to the dislocations and again form atmospheres that pin dislocation movement.

This chapter describes the ferritic microstructures that form in carbon steels under continuous cooling conditions. It begins with a review of the Dubé classification system for crystal morphologies. It then explains how cooling-rate-induced changes involving carbon atom diffusion and the associated rearrangement of iron atoms produce the wide variety of morphologies and microstructures observed in ferrite. The chapter also describes a classification system developed specifically for ferritic microstructures and uses it to compare common forms of ferrite, including polygonal or equiaxed ferrite, Widmanstatten ferrite, quasi-polygonal or massive ferrite, acicular ferrite, and granular ferrite.

This chapter is a compilation of beryllium phase diagrams, representing more than 25 binary alloy systems from beryllium-aluminum to beryllium-zirconium. Each diagram is presented along with a summary and source reference.

Titanium aluminides are lightweight materials that have relatively high melting points and good high-temperature strength. They also tend to be stronger and lighter than conventional titanium alloys, but considerably less ductile. This chapter begins with a review of the titanium-aluminum phase diagram, focusing on the properties, compositions, and microstructures of alpha-2 Ti3Al alloys. It then describes the properties, microstructures, and compositions of orthorhombic, gamma, and near-gamma alloys as well as the processing methods and procedures normally used in their production.

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.

Phases are distinct states of aggregation of matter and one of the primary leverage points for understanding and applying materials. This chapter discusses the phase nature of metals and alloys, the concept of solid solutions, and the use of phase diagrams. It also describes some of the metallurgical effects of freezing or solidification, including the segregation of solutes and the formation of metal glasses.

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 chapter describes the iron-carbon phase diagram, its modification by alloying elements, and the effect of carbon on the chemistry and crystallography of austenite, ferrite, and cementite found in Fe-C alloys and steels. It also lays the groundwork for understanding important metallurgical concepts, including solubility, critical temperature, dislocation defects, slip, and diffusion, and how they affect the microstructure, properties, and behaviors of steel.

Nonferrous alloys are heat treated for a variety of reasons. Heat treating can reduce internal stresses, redistribute alloying elements, promote grain formation and growth, produce new phases, and alter surface chemistry. This chapter describes heat treatment processes and how nonferrous alloys respond to them. It provides information on aluminum, cobalt, copper, magnesium, nickel, and titanium alloys and their composition, microstructure, properties, and processing characteristics.

Copper is often used in the unalloyed form because pure copper is more conductive than copper alloys. Alloying elements are added to optimize strength, ductility, and thermal stability, with little negative effect on other properties such as conductivity, fabricability, and corrosion resistance. This chapter covers the classification, composition, properties, and applications of copper alloys, including brasses, bronzes, copper-nickel, beryllium-copper, and casting alloys. It also examines wrought copper alloys and pure coppers. The chapter begins with an overview of the copper production process and concludes with a discussion on corrosion resistance.