This article describes the characterization of welds as a sequence of procedures, where each procedure is concerned with a finer scale of detail. The first level of characterization involves information that may be obtained by direct visual inspection and measurement of the weld. The article discusses nondestructive evaluation of welds by encompassing techniques that are used to characterize the locations and structure of internal and surface defects, including radiography, ultrasonic testing, and liquid penetrant inspection. It reviews the macrostructural characterization of a sectioned weld, including features such as number of passes; weld bead size, shape, and homogeneity; and the orientation of beads in a multipass weld. The article provides examples that describe how welds are characterized according to the procedures.

Optical metallography, one of the most common materials characterization techniques, uses visible light to magnify structural features of interest. This article discusses the use of optical methods to evaluate micro and macrostructure and relate it to process conditions and material behavior. It covers the steps involved in sample preparation, including sectioning, mounting, grinding, polishing, and etching, and presents several examples of macro and microanalysis on various metals and alloys.

The process of fatigue failure consists of three stages: initial fatigue damage leading to crack initiation; crack propagation to some critical size; and final, sudden fracture of the remaining cross section. Variations in mechanical properties, composition, microstructure, and macrostructure, along with their subsequent effects on fatigue life, have been studied extensively to aid in the appropriate selection of steel to meet specific end-use requirements. The metallurgical variables having the most pronounced effects on the fatigue behavior of carbon and low-alloy steels are strength, ductility, cleanliness, residual stresses, surface conditions, and aggressive environments. The article discusses the stress-based and strain-based approach to fatigue. The application of fatigue data in engineering design is complicated by the characteristic scatter of fatigue data; variations in surface conditions of actual parts; variations in manufacturing processes such as bending, forming, and welding; and the uncertainty of environmental and loading conditions in service.

Thermite welding (TW) is a fusion welding process in which two metals become bonded after being heated by superheated metal that has experienced an aluminothermic reaction. This article describes the thermite welding principles by presenting equations of the aluminothermic reaction that occurs in thermite welding. It provides information on the applications of thermite welding: rail welding, electrical connections, and railroad applications. The article concludes with a discussion on the associated safety aspects.

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.

Conventional high-strength aluminum alloys produced via powder metallurgy (P/M) technologies, namely, rapid solidification (RS) and mechanical alloying (mechanical attrition) have high strength at room temperature and elevated temperature. This article focuses on the metallurgy and weldability of dispersion-strengthened aluminum alloys based on the aluminum-iron system that are produced using various RS-P/M processing techniques. It describes weldability issues related to weld solidification behavior, the formation of hydrogen-induced porosity in the weld zone, and the high-temperature deformation behavior of these alloys, which affect the selection and application of fusion and solid-state welding processes. The article provides specific examples of material responses to welding conditions and highlights the microstructural development in the weld zone.

This article describes two methods based on rolling of sheet. The first is roll welding, where two or more sheets or plates are stacked together and then passed through rolls until sufficient deformation has occurred to produce solid-state welds. The other is laser roll welding, which is a hybrid process based on a thin-melting interface for a lap joint of dissimilar-metal sheets using a roller and one-sided laser heating. The article discusses the types, advantages, and applications of roll welding and laser roll welding. It also provides a detailed discussion on the laser roll welding of dissimilar metals.

This article describes the roll forming of components of nickel, titanium, and aluminum alloys. The metallurgical characteristics of the roll formed components, such as macrostructures, microstructures, tensile strength, and stress rupture performance, are discussed. The article compares the resulting properties of roll formed and conventionally forged components.

Diffusion brazing (DFB) is a process that coalesces, or joins, metals by heating them to a suitable brazing temperature at which either a preplaced filler metal will melt and flow by capillary attraction or a liquid phase will form in situ between one faying surface and another. This article discusses the two critical aspects of DFB, namely, a liquid filler metal must be formed and become active in the joint area and extensive diffusion of filler metal elements into the base metal must occur. It schematically illustrates a diffusion process that results in the loss of identity of original brazed joint. The article also discusses the advantages of DFB.

Manufacturing processes typically involve the reshaping of materials from one form to another under a set of processing conditions. This article discusses the two classification schemes of modeling for manufacturing processes, namely, on-line or off-line models and empirical, mechanistic, or deterministic models along with their important considerations. It describes the various aspects of modeling of deformation processes, casting operations, and fusion welding processes, with examples.