This article provides an overview of metal additive manufacturing (AM) processes and describes sources of failures in metal AM parts. It focuses on metal AM product failures and potential solutions related to design considerations, metallurgical characteristics, production considerations, and quality assurance. The emphasis is on the design and metallurgical aspects for the two main types of metal AM processes: powder-bed fusion (PBF) and directed-energy deposition (DED). The article also describes the processes involved in binder jet sintering, provides information on the design and fabrication sources of failure, addresses the key factors in production and quality control, and explains failure analysis of AM parts.

This article provides information on the metallurgy of austenitic stainless steels, and the formation of their intermediate phases (Sigma, Chi, and Laves). It discusses sensitization, a major problem associated with the austenitics, and solutions to avoid the problem. The article describes heat treatments applied to austenitic stainless steels, namely, soaking for homogenization and preparation for hot working; annealing to remove the effects of cold work and to put alloying elements into solid solution; and stress relieving. It provides information on the stabilizing anneal process, which is conducted on stabilized alloys, and discusses the metallurgical characteristics of austenitic stainless steels that may affect the selection of a stress-relieving treatment and prevention of stress corrosion by stress relieving. The article also discusses the heat treatments applied to duplex stainless steels, which involve soaking and annealing, achieving the austenite-ferrite balance, precipitation of intermetallics, and alpha prime precipitation.

This article commences with a description of the applications of galvanized coatings and provides information on metallurgical characteristics, such as coating thickness and alloying elements. It examines the effect of galvanizing process on the mechanical properties of steels and briefly describes the cleaning procedures of iron and steel pieces, before galvanizing. The article discusses the different types of conventional batch galvanizing practices. Information on the galvanizing of silicon-killed steels is also presented. The article concludes with helpful information on batch galvanizing equipment and galvanizing post treatments.

This article describes the classification of ferritic stainless steels. It reviews the metallurgical characteristics of various ferritic grades as well as the factors that influence their weldability. The article provides a discussion on various arc welding processes. These processes include gas-tungsten arc welding (GTAW), gas-metal arc welding (GMAW), flux-cored arc welding (FCAW), shielded metal arc welding (SMAW), and plasma arc welding (PAW). The selection criteria for welding consumables are discussed. The article also explains the welding procedures associated with the ferritic stainless steels. It concludes with information on weld properties.

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.

Heat treatment of depleted uranium (DU) alloys with 4.0 wt% or more molybdenum or equivalent is similar to that of dilute alloys. This article discusses the metallurgical characteristics and processing considerations of DU and its alloys, and describes the control of grain size and orientation using beta treatment. It lists the typical mechanical properties of DU as functions of the amount of cold work and hardness data of uranium rod, and describes the annealing of cold-worked DU. The article also describes the heat treatment of dilute alloys of DU, focusing on the three basic furnace designs used for heating or heat treating of unalloyed uranium: molten salt baths, inert-atmosphere furnaces, and vacuum furnaces. Finally, it presents procedures that are examples of heat treatment used to meet certain specifications of ultimate tensile strength, yield strength, and elongation.

The choice of heat treatment depends on the service requirements of a given bearing and how the bearing will be made. This article describes the design parameters, material characteristics required to sustain performance characteristics, metallurgical properties, and dimensional stability. It also provides a description of various extensively-used heat treatment processes, namely, carburizing, carbonitriding, induction surface hardening, and nitriding associated with various bearings. In addition, the article explores the factors to be considered in selecting a process and explains why it is optimum for a specific application.

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.

Explosion welding (EXW) is a solid-state metal-joining process that uses explosive force to create an electron-sharing metallurgical bond between two metal components. This article discusses the process attributes of EXW, including metallurgical attributes, metal combinations, size limitations, configuration limitations, and bond zone morphology. It provides an overview of the common industrial applications and shop welding applications of EXW products. The article reviews different safety standards and regulations, such as noise and vibration abatement and process geometry. It concludes with a section on the EXW process sequence for welding a two-component flat plate product.

The term cast iron designates a group of materials that contain more than one constituent in their microstructure due to excess carbon that result in unique characteristics such as the fracture appearance and graphite morphology. This article discusses the classification of cast iron and the various metallurgical aspects, such as the composition, alloying element, solidification, and graphite morphologies, of different types of cast iron. It describes the physical properties for various cast irons and the influence of microstructure and chemical composition on each property. The article provides a detailed account on thermal properties, conductive properties, magnetic properties, and acoustic properties of cast iron. It also examines heat treatment, namely, stress relieving, annealing, normalizing, through hardening, and surface hardening. The article presents a discussion on the welding, machining and grinding, and coating of the types of cast iron.

This article provides an overview of the effects of various material- and process-related parameters on residual stress, distortion control, cracking, and microstructure/property relationships as they relate to various types of failure. It discusses phase transformations that occur during heat treating and describes the metallurgical sources of stress and distortion during heating and cooling. The article summarizes the effect of materials and the quench-process design on distortion and cracking and details the effect of cooling characteristics on residual stress and distortion. It also provides information on the methods of minimizing distortion and tempering. The article concludes with a discussion on the effect of heat treatment processes on microstructure/property-related failures.

This article describes the preliminary stages and general procedures, techniques, and precautions employed in the investigation and analysis of metallurgical failures that occur in service. The most common causes of failure characteristics are described for fracture, corrosion, and wear failures. The article provides information on the synthesis and interpretation of results from the investigation. Finally, it presents key guidelines for conducting a failure analysis.

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.

This article discusses the use of a shaped electrode for electrical discharge machining (EDM). It describes the operational methodology of the EDM. Topography, metallurgical and chemical effects, and surface integrity of the EDM surface are reviewed. The article provides information on the characteristics of electrodes and the process features of electrode manufacturing. Functions of the dielectric fluids and applications of the EDM are discussed. The article reviews the advancement in EDM such as no-wear EDM and computer numerically controlled vertical EDM. It analyzes the applications and process of the traveling wire EDM. Health and safety measures for the EDM process are also discussed.

Electroless nickel plating is used to deposit nickel without the use of an electric current. This article provides an overview of the solution composition and characteristics of the electroless nickel bath. It focuses on the metallurgical, mechanical and physical properties of electroless nickel-phosphorus coatings and electroless nickel-boron coatings. The effect of electroless nickel coatings on the fatigue strength of steel is also described. The article includes information on the recommended pretreatment procedures for different ferrous alloys, aluminum alloys, and copper alloys. It presents a detailed account of the equipment and various processes—including bulk and barrel plating—involved in electroless nickel plating, and discusses hydrogen relief methods. The article includes a comprehensive table on nickel plating applications, and concludes with information on electroless nickel coatings on composites and plastics.

Cutting fluids play a major role in increasing productivity and reducing costs by making possible the use of higher cutting speeds, higher feed rates, and greater depths of cut. After listing the functions of cutting fluids, this article then covers the major types, characteristics, advantages and limitations of cutting and grinding fluids, such as cutting oils, water-miscible fluids, gaseous fluids, pastes, and solid lubricants along with their subtypes. It discusses the factors considered during the selection of cutting fluid, focusing on machinability (or grindability) of the material, compatibility (metallurgical, chemical, and human), and acceptability (fluid properties, reliability, and stability). The article also describes various application methods of cutting fluids and precautions that should be observed by the operator.

The principal types of elevated-temperature mechanical failure are creep and stress rupture, stress relaxation, low- and high-cycle fatigue, thermal fatigue, tension overload, and combinations of these, as modified by environment. This article briefly reviews the applied aspects of creep-related failures, where the mechanical strength of a material becomes limited by creep rather than by its elastic limit. The majority of information provided is applicable to metallic materials, and only general information regarding creep-related failures of polymeric materials is given. The article also reviews various factors related to creep behavior and associated failures of materials used in high-temperature applications. The complex effects of creep-fatigue interaction, microstructural changes during classical creep, and nondestructive creep damage assessment of metallic materials are also discussed. The article describes the fracture characteristics of stress rupture. Information on various metallurgical instabilities is also provided. The article presents a description of thermal-fatigue cracks, as distinguished from creep-rupture cracks.

Stress-corrosion cracking (SCC) is a form of corrosion and produces wastage in that the stress-corrosion cracks penetrate the cross-sectional thickness of a component over time and deteriorate its mechanical strength. Although there are factors common among the different forms of environmentally induced cracking, this article deals only with SCC of metallic components. It begins by presenting terminology and background of SCC. Then, the general characteristics of SCC and the development of conditions for SCC as well as the stages of SCC are covered. The article provides a brief overview of proposed SCC propagation mechanisms. It discusses the processes involved in diagnosing SCC and the prevention and mitigation of SCC. Several engineering alloys are discussed with respect to their susceptibility to SCC. This includes a description of some of the environmental and metallurgical conditions commonly associated with the development of SCC, although not all, and numerous case studies.

This article describes the factors considered in the analysis of brazeability and solderability of engineering materials. These are the wetting and spreading behavior, joint mechanical properties, corrosion resistance, metallurgical considerations, and residual stress levels. It discusses the application of brazed and soldered joints in sophisticated mechanical assemblies, such as aerospace equipment, chemical reactors, electronic packaging, nuclear applications, and heat exchangers. The article also provides a detailed discussion on the joining process characteristics of different types of engineering materials considered in the selection of a brazing process. The engineering materials include low-carbon steels, low-alloy steels, and tool steels; cast irons; aluminum alloys; copper and copper alloys; nickel-base alloys; heat-resistant alloys; titanium and titanium alloys; refractory metals; cobalt-base alloys; and ceramic materials.

This article discusses the general welding characteristics and metallurgical welding considerations that play an important function during the welding of nickel, nickel-copper, nickel-chromium, and nickel-chromium-iron alloys.