This article describes the three solidification mechanisms of peritectic structures, namely, peritectic reaction, peritectic transformation, and direct precipitation. It discusses the theoretical analysis, which shows that the rate of the peritectic transformation is influenced by the diffusion rate and the extension of the beta-phase region in the phase diagram. The article also provides information on the peritectic transformations in multicomponent systems.

Solid-state transformations from invariant reactions are of three types: eutectoid, peritectoid, and monotectoid transformations. This article focuses on structures from eutectoid transformations with an emphasis on the classic iron-carbon system of steel. It illustrates the morphology of a pearlite nodule and the effect of various substitutional alloy elements on the eutectoid transformation temperature and effective carbon content, respectively. Peritectic and peritectoid phase equilibria are very common in several binary systems. The article reviews structures from peritectoid reactions and details the formation of peritectic structures that can occur by at least three mechanisms: peritectic reaction, peritectic transformation, and direct precipitation of beta from the melt.

Similar to the eutectic group of invariant transformations is a group of peritectic reactions, in which a liquid and solid phase decomposes into a solid phase on cooling through the peritectic isotherm. This article describes the equilibrium freezing and nonequilibrium freezing of peritectic alloys. It informs that peritectic reactions or transformations are very common in the solidification of metals. The article discusses the formation of peritectic structures that can occur by three mechanisms: peritectic reaction, peritectic transformation, and direct precipitation of beta from the melt. It provides a discussion on the peritectic structures in iron-base alloys and concludes with information on multicomponent systems.

Two high-strength low-alloy (HSLA) families, acicular-ferrite steels and pearlite-reduced steels, contain microalloying additions of vanadium and niobium. Vanadium, niobium, and titanium combine preferentially with carbon and/or nitrogen to form a fine dispersion of precipitated particles in the steel matrix. This article summarizes the metallurgical effects of vanadium, niobium, molybdenum, and titanium. The metallurgical fundamentals were first applied to forgings in the early 1970s. The ultimate strength of first- and second-generation microalloy steels is adequate for many engineering applications, but these steels do not achieve the toughness of conventional quenched and tempered alloys under normal hot-forging conditions. Third-generation microalloy steels differ from their predecessors in that they are direct quenched from the forging temperature to produce microstructures of lath martensite with uniformly distributed temper carbides. Without subsequent heat treatment, these materials achieve properties, including toughness, similar to those of standard quenched and tempered steels.

Aluminum and aluminum alloys are very suitable for extrusion and many types of profiles can be produced from easily extrudable alloys. This article lists the basic characteristics of aluminum and its alloys. It tabulates the aluminum extrusion alloys by series and lists the typical applications for 6xxx series aluminum extrusions. The article discusses three broad categories of extrusion profiles: solid profile, hollow profile, and semi hollow profile. It provides information on weldability and machinability, which are often considered in profile design and product performance. The article discusses different aluminum extrusion processes, such as the direct extrusion process and the indirect extrusion process. It schematically illustrates the plotting of flow stress and extrudability for several types of aluminum alloys. The article concludes with information on the heat treatment and precipitation hardening for alloys, such as 2xxx, 6xxx, and 7xxx.

This article reviews the types of passivity and presents tactics that employ passivity to control corrosion. Thermodynamics provides a guide to the conditions under which passivation becomes possible. A valuable guide to thermodynamics is the potential-pH diagram and the Pourbaix diagram. The article presents a potential-pH diagram for the iron-water system and an illustration of an idealized anodic polarization curve for a metal surface, which serves as a basis for describing the kinetics of passivation. It discusses five properties of passive films: thickness, composition, structure, electronic properties, and mechanical properties. The article outlines three possible processes that can form passive films: direct film formation, dissolution precipitation, and anodic oxidation of metal ions in solution. It describes the breakdown of the passive film using various models and highlighting the effect of alloy composition and structure.

Metallic alloys that are typically used for medical purposes include stainless steels, Ti-6Al-4V, and Co-Cr-Mo. This article discusses the relative merits of each of these alloys. The utilization of stainless steels in the biomedical industry, especially in relation to the additive manufacturing (AM) process, is the main focus of this article. The characteristics of various stainless steels are described subsequently, and the categories that are of relevance to the biomedical industry are identified. The types of stainless steels covered are austenitic, ferritic, martensitic, duplex, and precipitation-hardened stainless steels. The article discusses the potential benefits of AM for biomedical devices. It describes the types of AM processes for stainless steels, namely binder jet, directed-energy deposition, and laser powder-bed fusion. The article reviews the AM of austenitic, martensitic, and PH stainless steels for biomedical applications. In addition, the challenges and obstacles to the clinical use of AM parts are covered.

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 begins with a schematic illustration of a eutectic system in which the two components of the system have the same crystal structure. Eutectic systems form when alloying additions cause a lowering of the liquidus lines from both melting points of the pure elements. The article describes the aluminum-silicon eutectic system and the lead-tin eutectic system. It discusses eutectic morphologies in terms of lamellar and fibrous eutectics, regular and irregular eutectics, and the interpretation of eutectic microstructures. The article examines the solidification of a binary alloy of exactly eutectic composition. It concludes with a discussion on terminal solid solutions.

This article aims to summarize the work on cryogenic strength and toughness and to present the fractography of aluminum alloys. It presents case studies on the importance of understanding the fractography of aluminum alloys and the role of microstructure in the appearance of fractographic features, with variables comprised of in-plane/through-thickness anisotropy, test temperature, heat treatment condition, and the effect of welding.

In high-strength aluminum alloys, stress-corrosion cracking (SCC) is known to occur in ordinary atmospheres and aqueous environments. This article discusses the mechanisms of SCC in aluminum alloys, providing information on two main types of SCC models: those of anodic dissolution based on electrochemical theory and those that involve the stress-sorption theory of mechanical fracture. It reviews three different categories of experiments used to compare SCC performance of candidate materials for service. The categories are tests on statically loaded smooth samples, tests on statically loaded precracked samples, and tests using slowly straining samples. The article describes SCC susceptibility and ratings of SCC resistance for high-strength wrought aluminum products, such as 2xxx, 5xxx, and 7xxx series alloys, aluminum-lithium alloys, and 7xxx alloys containing copper.

This article briefly introduces the concept of creep properties of additively manufactured (AM) alloys, with a focus on the effects of the characteristic microstructure of AM alloys on creep performance. Relevant postprocessing treatment also is discussed, in relation to improved creep performance based on the improvement of AM initial microstructure.

This article discusses fracture, fatigue, and creep of nickel-base superalloys with additional emphasis on directionally solidified and single-crystal applications. It analyzes the physical metallurgy of these alloys. The effects of grain boundary and grain size on failure are summarized. The article also discusses the effects of microstructure and extrinsic parameters on fatigue crack propagation (FCP). It details the modeling of FCP rates and creep and creep-fatigue crack growth rates.

Aluminum-lithium alloys have been developed primarily to reduce the weight of aircraft and aerospace structures. This article commences with a discussion on the physical metallurgy and development of aluminum-lithium alloys. It focuses on major commercial aluminum-lithium alloys, including alloy 2090, alloy 2091, alloy 8090, alloy CP276, and Weldalite 049. The article also lists the chemical compositions, physical properties, fabrication characteristics, corrosion performance, and general applications of these alloys. A comparison of alloy properties is represented graphically.

This article presents various equations that are essential for the modeling of both single-phase and multiphase profiles. It includes the fundamental laws of diffusion, along with its equations and solutions. The article provides information on the series of applications that illustrate how various diffusional processes can be modeled.