The formation of defects within additive-manufactured (AM) components is a major concern for critical structural and cyclic load applications. Thus, understanding the mechanisms of defect formation in fusion-based processes is important for prescribing the appropriate process parameters specific to the alloy system and selected processing technique. This article discusses the formation of defects within metal additive manufacturing, namely fusion-based processes and solid-state/sintering processes. Defects observed in fusion-based processes include lack of fusion, keyhole collapse, gas porosity, solidification cracking, solid-state cracking, and surface-connected porosity. The types of defects in solid-state/sintering processes are sintering porosity and improper binder burnout. The article also discusses defect-mitigation strategies, such as postprocess machining, surface treatment, and postprocessing HIP to eliminate defects detrimental to properties from the as-built condition. The use of noncontact thermal, optical, and ultrasound techniques for inspecting AM components are also considered. The final section summarizes the knowledge gap in our understanding of the defects observed within AM components.

Submerged arc welding (SAW) is an arc welding process in which the arc is concealed by a blanket of granular and fusible flux. This article provides a schematic illustration of a typical setup for automatic SAW and discusses the advantages and limitations and the process applications of SAW. The article discusses flux classification relative to production method, relative to effect on alloy content of weld deposit, and relative to basicity index. It describes the procedural variations and the effect of weld current, weld voltage, electrical stickout, travel speed, and flux layer depth on weld bead characteristics. The article concludes with information on weld defects, such as lack of fusion, slag entrapment, solidification cracking, hydrogen cracking, or porosity.

This article addresses consumable selection and procedure development for the welding of stainless steels. The WRC-1992 diagram and the Schaeffier diagram, are used to illustrate the rationale behind many filler-metal choices. The article discusses the basic metallurgy and base metals of five major families of stainless steels: martensitic stainless steels, ferritic stainless steels, austenitic stainless steels, precipitation-hardening (PH) stainless steels, and duplex ferritic-austenitic stainless steels. Stainless steels of all types are weldable by virtually all welding processes. The article describes the common arc welding processes with regard to procedure and technique errors that can lead to loss of ferrite control with the common austenitic stainless steel weld metals that are designed to contain a small amount of ferrite for protection from hot cracking. The arc welding processes include shielded-metal arc welding, gas-tungsten arc welding, and gas-metal arc welding.

Austenitic stainless steels exhibit a single-phase, face-centered cubic structure that is maintained over a wide range of temperatures. This article reviews the compositions of standard and nonstandard austenitic stainless steels. It summarizes the important aspects of solidification behavior and microstructural evolution that dictate weld-metal ferrite content and morphology. The article describes weld defect formation, namely, solidification cracking, heat-affected zone liquation cracking, weld-metal liquation cracking, copper contamination cracking, ductility dip cracking, and weld porosity. It discusses four general types of corrosive attack: intergranular attack, stress-corrosion cracking, pitting and crevice corrosion, and microbiologically influenced corrosion. The article concludes with information on weld thermal treatments such as preheat and interpass heat treatments and postweld heat treatment.

This article discusses four types of defects in materials that have been fusion welded and that have been the focus of much attention because of the magnitude of their impact on product quality. These include hot cracks, heat-affected zone (HAZ) microfissures, cold cracks, and lamellar tearing. These defects, all of which manifest themselves as cracks, are characteristic of phenomena that occur at certain temperature intervals specific to a given alloy. The article presents selected alloy 625 compositions used in weldability study.

This article discusses two categories of stainless steel casting alloys and their nomenclature. It provides information on two situations in which welding of stainless steel castings is required. These situations are based on casting defects and selection of welding processes. The article presents compositions and typical microstructures of corrosion-resistant stainless steel casting alloys in tabular form. It presents special considerations for the welding of martensitic stainless steel castings. The article reviews the two most serious problems encountered in the welding of stainless steel castings, namely, solidification hot cracking and heat-affected zone hot cracking. It concludes with a discussion on the some useful considerations for welding corrosion-resistant alloys to avoid defects.

This article focuses on the tests for evaluating the weldability, cracking susceptibility, weld pool shape, fluid flow, and weld penetration of base materials. These tests include different types of self-restraint tests, externally loaded tests for evaluating cracking susceptibility and weld penetration tests, weld pool shape tests, and Gleeble testing for evaluating weld pool shape, fluid flow, and weld penetration.

This article discusses the susceptibility of carbon steels to hydrogen-induced cracking, solidification cracking, lamellar tearing, weld metal porosity, and heat-affected zone (HAZ) mechanical property variations. The composition and mechanical properties of selected carbon steels used in arc welding applications are listed in a table. The article presents process selection guidelines for arc welding carbon steels. It provides information on the shielded metal arc welding, gas-metal arc welding, and flux-cored arc welding, gas-tungsten arc and plasma arc welding, submerged arc welding, electrogas welding, electroslag welding, and stud arc welding.

This article describes the common defects associated with arc welds in the weld metal and the heat-affected zone (HAZ) of the plate. These defects include porosity, incomplete fusion, hot cracks, lamellar tearing, undercut, rollover, and inclusions. The article details hydrogen-induced cracking and its mechanism as well as the control measures. It provides information on measurement of hydrogen in weld metal and presents a table that contain information on effect of welding processes and electrodes on hydrogen levels in welds.

This article is a guide to the welding of commercially available aluminum-lithium alloys. It discusses the weldability issues created by weld porosity, hot cracking, and filler metal selection and presents the data revealed from weld characterization.

This article aims to survey the factors controlling the weldability of carbon and low-alloy steels in arc welding. It discusses the influence of operational parameters, thermal cycles, and metallurgical factors on weld metal transformations and the susceptibility to hot and cold cracking. The article addresses the basic principles that affect the weldability of carbon and low-alloy steels. It outlines the characteristic features of welds and the metallurgical factors that affect weldability. It describes the common tests to determine steel weldability. There are various types of tests for determining the susceptibility of the weld joint to different types of cracking during fabrication, including restraint tests, externally loaded tests, underbead cracking tests, and lamellar tearing tests. Weldability tests are conducted to provide information on the service and performance of welds. The major tests that are discussed in this article are weld tension test, bend test, the drop-weight test, the Charpy V-notch test, the crack tip opening displacement test, and stress-corrosion cracking test.