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 describes important requirements for ferrous and nonferrous alloys used for gears. Wrought surface-hardening and through-hardening carbon and alloy steels are the most widely used of all gear materials and are emphasized in this chapter. The processing characteristics of gear steels and the bending fatigue strength and properties of carburized steels are reviewed. In addition to wrought steels, the chapter provides information on the other iron-base alloys that are used for gears, namely cast carbon and alloy steels, gray and ductile cast irons, powder metallurgy irons and steels, stainless steels, and tool steels. In terms of nonferrous alloys, the chapter addresses copper-base alloys, die cast aluminum alloys, zinc alloys, and magnesium alloys.

Several components from the tail boom of a helicopter were found fractured at a crash site, including gusset plates, the hat section near the lower yoke, and a cable that controls the pitch of the tail rotor. The components were recovered from the wreckage and taken to a lab for closer examination. Based on their observations and the results of SEM fractography, failure analysts concluded that the gusset plates failed due to a downward bending overload in tension and that the tail rotor control cable snapped due to tensile overload. There were no indications of delayed failure in any of the areas examined.

The mechanical behavior of a material, in the most practical sense, is how it deforms or breaks under load; in other words, how it responds when stressed. This chapter provides a brief review of the properties associated with mechanical behavior, including stress, strain, elasticity, plastic deformation, ductility, hardness, creep, fatigue, and fracture. It also describes the primary components of a Charpy impact tester and the role they serve.

In order to understand how various types of single-load fractures are caused, one must understand the forces acting on the metals and also the characteristics of the metals themselves. All fractures are caused by stresses. Stress systems are best studied by examining free-body diagrams, which are simplified models of complex stress systems. Free-body diagrams of shafts in the pure types of loading (tension, torsion, and compression) are the simplest; they then can be related to more complex types of loading. This chapter discusses the principles of these simplest loading systems in ductile and brittle metals.

Ductile fracture results from the application of an excessive stress to a metal that has the ability to deform permanently, or plastically, prior to fracture. Careful examination and knowledge of the metal, its thermal history, and its hardness are important in determining the correct nature of the fracture features. This chapter is a detailed account of the general characteristics and microstructural aspects of ductile fracture with suitable illustrations. It describes some of the complicating factors extraneous to the fracture itself.

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.

This chapter discusses the factors that play a role in fatigue failures and how they affect the service life of metals and structures. It describes the stresses associated with high-cycle and low-cycle fatigue and how they differ from the loading profiles typically used to generate fatigue data. It compares the Gerber, Goodman, and Soderberg methods for predicting the effect of mean stress from bending data, describes the statistical nature of fatigue measurements, and explains how plastic strain causes cyclic hardening and softening. It discusses the work of Wohler, Basquin, and others and how it led to the development of a strain-based approach to fatigue and the use of fatigue strength and ductility coefficients. It reviews the three stages of fatigue, beginning with crack initiation followed by crack growth and final fracture. It explains how fracture mechanics can be applied to crack propagation and how stress concentrations affect fatigue life. It also discusses fatigue life improvement methods and design approaches.

The design of case-hardened components is an iterative process, requiring the consideration of multiple interrelated factors. This chapter walks readers through the steps involved in selecting an appropriate material and assessing the influence of alloy composition and cooling rate on core properties including hardenability, microstructure, tensile and yield strength, ductility, toughness, and fatigue resistance. It likewise explains how carbon affects case hardenability, surface hardness, and case toughness and how case depth influences residual stresses and bending and contact fatigue. It also discusses the effect of quenching methods and addresses the issue of distortion.

Metals are used in many engineering applications because of their mechanical properties, particularly strength and ductility. This chapter explains how mechanical properties are measured and how to interpret the results. It describes the most widely used tests, including tensile tests; Rockwell, Brinell, Vickers, and Knoop hardness tests; and Charpy V-notch impact tests. The chapter also provides information on loading conditions that can lead to fatigue failure, and in some cases, counteract or prevent it.

Tensile tests are performed for several reasons related to materials development, comparison, selection, and quality control. The properties derived from tensile tests are used in selecting materials for engineering applications. Tensile properties often are used to predict or estimate the behavior of a material under forms of loading other than uniaxial tension. This chapter provides a brief overview of tensile specimens and test machines, stress-strain curves, true stress and strain, and test methodology and data analysis.

This chapter describes the equipment and processes used to form titanium alloy parts. It discusses the advantages and disadvantages of hot and cold forming, the factors that influence formability, and the effect of forming temperature and lubricants. It describes common processes, including brake forming, stretch forming, deep drawing, and spin forming as well as roll forming, drop-hammer forming, tube bulging and bending, and superplastic forming. It also discusses dimpling and joggling and the use of hot sizing to correct springback.