In some phase diagrams, the appearance of several reactions is the result of the presence of intermediate phases. These are phases whose chemical compositions are intermediate between two pure metals, and whose crystalline structures are different from those of the pure metals. This article describes the order-disorder transformation that typically occurs on cooling from a disordered solid solution to an ordered phase. It provides a table that lists selected superlattice structures and alloy phases that order according to each superlattice. The article informs that spinodal decomposition has been particularly useful in the production of permanent magnet materials, because the morphologies favor high magnetic coercivities. It also describes the theory of spinodal decomposition with a simple binary phase diagram.

Spinodal transformation is a phase-separation reaction that occurs from kinetic behavior. This article discusses the theory of spinodal decomposition, and outlines the methods used in the characterization of spinodal structures in metal matrices.

This introductory article provides basic information on the various aspects of solid-state transformation: multiphase microstructures, substructures, and crystallography, which assist in characterizing the morphology of phase transformations. It contains a flowchart that illustrating the classification of transformations by growth processes.

This article presents the experimental and theoretical aspects of small-angle scattering, and discusses specific applications used in the characterization of metals, glasses, polymers, and ceramics. The basic methods of collimating x-rays, the cause of smearing from a line source, desmearing parameters, and the types of scattering curves are illustrated.

This article is an atlas of fractographs that helps in understanding the causes and mechanisms of fracture of copper alloys and in identifying and interpreting the morphology of fracture surfaces. The fractographs illustrate the following: fatigue fracture, intergranular fracture, transgranular fracture, microvoid coalescence, corrosion fatigue, fatigue striations, tensile-overload fracture, stress-corrosion cracking, and pitting corrosion of these alloys.

This article introduces the mechanism of diffusion and the common types of heat treatments such as annealing and precipitation hardening, which are applicable to most ferrous and nonferrous systems. Three distinct processes occur during annealing: recovery, recrystallization, and grain growth. The article also describes the various types of solid-state transformations such as isothermal transformation and athermal transformation, resulting from the heat treatment of nonferrous alloys. It provides information on the homogenization of chemical composition within a cast structure.

This article provides information on the Unified Numbering System designations and temper designations of copper and copper alloys. It discusses the basic types of heat treating processes of copper and copper alloys, namely, homogenizing, annealing, and stress relieving, and hardening treatments such as precipitation hardening, spinodal hardening, order hardening, and quench hardening and tempering. The article presents tables that list the compositions and mechanical properties of copper alloys. It also discusses two strengthening mechanisms of copper alloys, solid-solution strengthening and work hardening. Finally, the article provides information on the equipment used for the heat treating of copper and copper alloys, including batch-type atmosphere furnaces, continuous atmosphere furnaces, and salt baths.

This article describes the integration of thermodynamic modeling, mobility database, and phase-transformation crystallography into phase-field modeling and its combination with transformation texture modeling to predict phase equilibrium, phase transformation, microstructure evolution, and transformation texture development during heat treatment of multicomponent alpha/beta and beta titanium alloys. It includes quantitative description of Burgers orientation relationship and path, discussion of lattice correspondence between the alpha and beta phases, and determination of the total number of Burgers correspondence variants and orientation variants. The article also includes calculation of the transformation strain with contributions from defect structures developed at alpha/beta interfaces as a precipitates grow in size. In the CALculation of PHAse Diagram (CALPHAD) framework, the Gibbs free energies and atomic mobilities are established as functions of temperature, pressure, and composition and serve directly as key inputs of any microstructure modeling. The article presents examples of the integrated computation tool set in simulating microstructural evolution.

This article describes the results obtained by Volmer, Weber, Farkas, Becker, and Doring, which constitute the classical nucleation theory. These results are the predictions of the precipitate size distribution, steady-state nucleation rate, and incubation time. The article reviews a nucleating system as a homogeneous phase using the classical nucleation theory, along with heterophase fluctuations that led to the formation of precipitates. It discusses the gas cluster dynamics using the kinetic approach to describe nucleation. The article presents key parameters, such as cluster condensation and evaporation rates, to describe the time evolution of the system. The predictions and extensions of the classical nucleation theory are discussed. The article also provides the limitations of classical nucleation theories in cluster dynamics.

Field ion microscopy (FIM) can be used to study the three-dimensional structure of materials, such as metals and semiconductors, because successive atom layers can be ionized and removed from the surface by field evaporation. The ions removed from the surface by field evaporation can be analyzed chemically by coupling to the microscope a time-of-flight mass spectrometer of single-particle sensitivity, known as the atom probe (AP). This article describes the principles, sample preparation, and quantitative analysis of FIM. It also provides information on the principles, instrument design and operation, mass spectra and their interpretation, and applications of AP microanalysis.

This article describes the fracture toughness behavior of austenitic stainless steels and their welds at ambient, elevated, and cryogenic temperatures. Minimum expected toughness values are provided for use in fracture mechanics evaluations. The article explains the effect of crack orientation, strain rate, thermal aging, and neutron irradiation on base metal and weld toughness. It discusses the effect of cold-work-induced strengthening on fracture toughness. The article examines the fracture toughness behavior of aged base metal and welding-induced heat-affected zones. It concludes with a discussion on the Charpy energy correlations for aged stainless steels.

Precipitation reactions occur in many different alloy systems when one phase transforms into a mixed-phase system as a result of cooling from high temperatures. This article discusses the homogenous and heterogeneous nucleation and growth of coherent and semicoherent precipitates. It describes two precipitation modes, namely, general or continuous precipitation and cellular or discontinuous precipitation. The article also provides information on the precipitation sequences in aluminum alloys.

This article describes the different types of precipitation and transformation processes and their effects that can occur during heat treatment of various nonferrous alloys. The nonferrous alloys are aluminum alloys, copper alloys, magnesium alloys, nickel alloys, titanium alloys, cobalt alloys, zinc alloys, and heat treatable silver alloys, gold alloys, lead alloys, and tin alloys. It also provides a detailed discussion on the effects due to precipitation and transformation processes in these non-ferrous alloys.

This article discusses the chief magnetic characteristics of permanent magnet materials. It provides a detailed description on nominal compositions; principal magnet designations; magnetic, physical, and mechanical properties; selection criteria; and applications of the permanent magnet materials, which include magnet steels, magnet alloys, alnico alloys, platinum-cobalt alloys, cobalt and rare-earth alloys, hard ferrites, iron-chromium-cobalt alloys, and neodymium-iron-boron alloys.

This article provides information on the general structural features and origins of metals. The characteristic structural features of single-phase metals and alloys, such as grain structure and substructure, are discussed. The article also describes the major types of multiphase structures and macrostructure of metals and alloys.