This article describes the development of heat-resistant titanium-base alloys and their classification into several microstructure categories based on their strengthening mechanisms. It explains the phase transformation in titanium-aluminum-base alloys and two peritectic reactions that take place in the titanium-aluminum system. The article also describes two approaches for controlling the orientation of the high-temperature alpha phase to achieve the required lamellar orientation by directional solidification in order to improve the strength and ductility of titanium-aluminum alloys. One approach is by seeding the alpha phase in the alloys, and the other is without seeding, by controlling the solidification path of alloys through appropriate alloying. The article discusses the grain refinement technique used to improve the ductility of cast titanium-aluminum alloys to a level of above 1" at room temperature and reasonable room temperature ductility in the as-cast condition. Finally, it provides information on the microstructures produced through various near-net shape manufacturing processes.

Computational modeling assists in addressing the issues of solid/liquid interface dynamics at the microlevel. It also helps to visualize the grain length scale, fraction of phases, or even microstructure transitions through microstructure maps. This article provides a detailed account of the general capabilities of the various models that can generate microstructure maps and thus transform the computer into a dynamic microscope. These include standard transport models, phase-field models, Monte Carlo models, and cellular automaton models.

This article provides a review of metallographic procedures and techniques for analyzing the microstructure of fusion welded joints. It discusses sample preparation, the use of backing plates, and common sectioning methods. It identifies the various types of defects that can occur in arc welded metals, organizing them according to the sectioning method by which they are observed. It describes the relationship between weld bead morphology and sectioning direction and its effect on measurement error. The article examines micrographs from stainless steel, aluminum, and titanium alloy joints, highlighting important details such as solidification and solid-state transformation structures and what they reveal about the welding process. Besides arc welding, it also discusses laser and electron beam welding methods, resistance and spot welding, and the welding of dissimilar metals.

Recovery, recrystallization, and grain growth are the stages that a cold worked metal undergoes when it is annealed. This article describes the changes in the structure and properties that occur on annealing a cold-worked metal. It summarizes the experimental recrystallization studies by Burke and Turnbull with six laws of recrystallization. Applications of these laws of recrystallization are discussed in detail with examples. The article reviews the classification of grain growth according to the growth behavior of grains, namely, normal or continuous grain growth and abnormal or discontinuous grain growth. The latter has also been termed exaggerated grain growth, coarsening, or secondary recrystallization.

The ferrous metals are the most significant class of commercial alloys. This article describes the solidification structures of plain carbon steel, low-alloy steel, high-alloy steel, and cast iron, with illustrations. The formation of nonmetallic inclusions in the liquid before and during solidification is also discussed.

The most common aluminum alloy systems are aluminum-silicon, aluminum-copper, and aluminum-magnesium. This article focuses on the grain structure, eutectic microstructure, and dendritic microstructure of these systems. It provides information on microsegregation and its problems in casting of alloys. The article also illustrates the casting defects such as macroporosity, microshrinkage, and surface defects, associated with the alloys.

Electroslag welding (ESW) and electrogas welding (EGW) are two related procedures that are used to weld thick-section materials in the vertical or near-vertical position between retaining shoes. This article discusses the fundamentals of the electroslag process in terms of heat flow conditions and metal transfer and weld pool morphology. It presents constitutive equations for welding current, voltage, and travel rate for ESW. The article describes the metallurgical and chemical reactions in terms of fusion zone compositional effects, weld metal inclusions, solidification structure, and solid-state transformations. It describes the electroslag process development and the applications of electroslag and electrogas processes. The article concludes with a discussion on weld defects, such as temper embrittlement, hydrogen cracking, and weld distortion.