This article discusses the weldability and fusion weld properties of refractory metal alloys. The alloys discussed include tantalum, niobium, rhenium, molybdenum, and tungsten.

This chapter covers the welding characteristics of titanium along with the factors that determine which welding method is most appropriate for a given application. It discusses the joinability of titanium alloys, the effect of heat on microstructure, the cause of various defects, and the need for contaminant-free surfaces and atmospheres. It describes common forms of fusion, arc, and solid-state welding along with the use of filler metals, shielding gases, and stress-relief treatments. It also discusses the practice of titanium brazing and the role of filler metals.

Superalloys, except those with high aluminum and titanium contents, are welded with little difficulty. They can also be successfully brazed. This chapter describes the welding and brazing processes most often used and the factors that must be considered when making application decisions. It discusses the basic concepts of fusion welding and the differences between solid-solution-hardened and precipitation-hardened wrought superalloys. It addresses joint integrity, design, weld-related cracking, and the effect of grain size, precipitates, and contaminants. It covers common fusion welding techniques, defect prevention, fixturing, heat treatments, and general practices, including the use of filler metals. It also discusses several solid-state welding methods, superplastic forming, and transient liquid phase bonding, a type of diffusion welding process. The chapter includes extensive information on brazing processes, atmospheres, filler metals, and surface preparation procedures. It also includes examples of nickel-base welded components for aerospace use.

Surface cleanliness requirements depend on which nitrocarburizing process is selected for component treatment. This chapter discusses the processes involved in some of the more commonly used precleaning methods for gas ferritic nitrocarburizing and provides information on the methods used to accomplish enhanced plasma cleaning.

The surface condition of metals can have a significant effect on the outcome of high-temperature processes and vice versa. This chapter discusses the general cleaning and surface treatment needs of work in-process both before and after induction hardening. It identifies contaminants and defects associated with various quenchants and processing atmospheres and provides insights on how they can be removed and, in some cases, prevented. It also recommends the application of a rust preventative shortly after parts have cooled.

Gas turbine disks made from nickel-base superalloys are often produced using powder metallurgy (P/M) techniques because the alloy compositions normally used are difficult or impractical to forge by conventional methods. This chapter discusses the P/M process and its application to superalloys. It describes the gas, vacuum, and centrifugal atomization processes used to make commercial superalloy powders. It explains how the powders are consolidated into preforms or billets using hot isostatic pressing, extrusion, or a combination of the two. It also provides information on spray forming and consolidation by atmospheric pressure, and includes a section on powder-based disk components, where it discusses the general advantages of P/M as well as the effects of inclusions, carbon contamination, and the formation of oxide and carbide films due to prior particle boundary conditions. The chapter concludes with a detailed discussion on mechanically alloyed superalloy compositions, the product forms into which they are made, and some of the applications where they are used.

All superalloys, whether precipitation hardened or not, are heated at some point in their production for a subsequent processing step or, as needed, to alter their microstructure. This chapter discusses the changes that occur in superalloys during heat treatment and the many reasons such changes are required. It describes several types of treatments, including stress relieving, in-process annealing, full annealing, solution annealing, coating diffusion, and precipitation hardening. It discusses the temperatures, holding times, and heating and cooling rates necessary to achieve the desired objectives of quenching, annealing, and aging along with the associated risks of surface damage caused by oxidation, carbon pickup, alloy depletion, intergranular attack, and environmental contaminants. It also discusses heat treatment atmospheres, furnace and fixturing requirements, and practical considerations, including heating and cooling rates for wrought and cast superalloys and combined treatments such as solution annealing and vacuum brazing.

This chapter discusses some important factors involved in the atmospheric corrosion of engineering materials. The discussion begins with a description of elements necessary for the operation of a galvanic corrosion cell and corrosion reactions, followed by the types of atmospheric corrosion attack. Some of the atmospheric parameters and their effects on the corrosion of several metals are then reviewed. The following sections provide information on air chemistry, principal pollutants inducing corrosion, thermodynamics as well as models for prediction of atmospheric corrosion, and use of Pourbaix diagrams. The phenomenon of precipitation runoff on the corroded metal surface is then discussed. The chapter also describes the role of microbes or bacteria in the corrosion of metals. It concludes by providing information on the trends in atmospheric corrosion research and methods.

This chapter explains how decarburization can occur during carburizing processes and how to limit the severity of its effects. It describes the reactions and conditions that result in a loss of carbon atoms and how they vary with changes in the physical metallurgy of the affected material and the processing environment. It examines the characteristic features of decarburized microstructures and assesses their influence on hardness, residual stresses, and fatigue and fracture behaviors. It also discusses corrective measures and practical considerations regarding their use.

Superalloys are susceptible to damage from a variety of surface contaminants. They may also require special surface finishes for subsequent processing steps such as coating applications. This chapter describes some of the cleaning and finishing procedures that have been developed for superalloys and how they work. It discusses the effect of metallic contaminants, tarnish, oxide, and scale and how they can be detected and removed. It also discusses chemical and mechanical surface finishing techniques and where they are used, and presents several application examples.

Arc welding applies to a large and diversified group of welding processes that use an electric arc as the source of heat to melt and join metals. This chapter provides a detailed overview of specific arc welding methods: shielded metal arc welding, flux cored arc welding, submerged arc welding, gas metal arc welding, gas tungsten arc welding, plasma arc welding, plasma-GMAW welding, electroslag welding, and electrogas welding. The basic characteristics of gases used for shielding during arc welding are briefly discussed.

This chapter, a detailed account of furnaces and related equipment for heat treating, begins by describing three basic modes of heat transmission, namely conduction, convection, and radiation, followed by a discussion on the working principle, applications, advantages, and disadvantages of furnaces classified based on the heat transfer medium employed. The types of furnaces covered are batch-type, continuous-type, liquid bath, fluidized bed, and vacuum. The subsequent sections provide information on furnace parts, fixtures, quenching mediums, and quenching systems. The final section of the chapter describes the types of atmospheres available, emphasizing their applications and limitations.

This article examines the composition and properties of magnesium and its alloys. It discusses alloy and temper designations, applications and product forms, and commercial alloy systems, and explains how alloying elements affect physical and mechanical properties, processing characteristics, and corrosion behaviors.

Aluminum products are used extensively in natural atmospheres and in and around water. They are also widely used in building materials and as containers for chemicals and food and beverage products. This chapter discusses the corrosion mechanisms associated with these environments and the influence of various factors and prevention methods. It also includes an extensive amount of data of corrosion rates, corrosion resistance, and changes in mechanical properties.

This article discusses the fusion welding processes that are most widely used for joining titanium, namely, gas-tungsten arc welding, gas-metal arc welding, plasma arc welding, laser-beam welding, and electron-beam welding. It describes several important and interrelated aspects of welding phenomena that contribute to the overall understanding of titanium alloy welding metallurgy. These factors include alloy types, weldability, melting and solidification effects on weld microstructure, postweld heat treatment effects, structure/mechanical property/fracture relationships, and welding process application.

Martensitic stainless steels are essentially iron-chromium-carbon alloys that possess a body-centered tetragonal crystal structure (martensitic) in the hardened condition. Martensitic stainless steels are similar to plain carbon or low-alloy steels that are austenitized, hardened by quenching, and then tempered for increased ductility and toughness. This chapter provides a basic understanding of grade designations, properties, corrosion resistance, and general welding considerations of martensitic stainless steels. It also discusses the causes for hydrogen-induced cracking in martensitic stainless steels and describes sulfide stress corrosion resistance of type 410 weldments.

This chapter covers regulatory requirements, safe handling practices, hazard analysis and control, dismantling and decommissioning, and waste disposal. It also includes references for additional information on government regulations.

Most integrated titanium mills have primary working equipment designed specifically for titanium. This chapter describes the forging, rolling, and extruding equipment used to produce titanium mill products and sheds light on the corresponding process, structure, property relationships.

This chapters reviews the various process, material, and post-treatment problems that can occur in nitriding and how to troubleshoot them. The troubleshooting methods discussed relate to gas nitriding, salt bath nitriding, and ion nitriding.

This chapter discusses the various methods used to join titanium alloy assemblies, focusing on welding processes and procedures. It explains how welding alters the structure and properties of titanium and how it is influenced by composition, surface qualities, and other factors. It describes several welding processes, including arc welding, resistance welding, and friction stir welding, and addresses related issues such as welding defects, quality control, and stress relieving. The chapter also covers mechanical fastening techniques along with adhesive bonding and brazing.