The solidification process has a major influence on the microstructure and mechanical properties of metal casting as well as wrought products. This appendix covers the fundamentals of solidification. It discusses the formation of solidification structures, the characteristics of planar, cellular, and dendritic growth, the basic freezing sequence for an alloy casting, and the variations in cooling rate, heat flow, and grain morphology in different areas of the mold. It also describes the types of segregation that occur during freezing, the effect of solidification rate on secondary dendrite arm spacing, and the factors that contribute to porosity and shrinkage.

Almost all metals and alloys are produced from liquids by solidification. For both castings and wrought products, the solidification process has a major influence on both the microstructure and mechanical properties of the final product. This chapter discusses the three zones that a metal cast into a mold can have: a chill zone, a zone containing columnar grains, and a center-equiaxed grain zone. Since the way in which alloys partition on freezing, it follows that all castings are segregated to different categories. The different types of segregation discussed include normal, gravity, micro, and inverse. The chapter also provides information on grain refinement and secondary dendrite arm spacing and porosity and shrinkage in castings. It concludes with a brief overview of six of the most important casting processes in industries: sand casting, plaster mold casting, evaporative pattern casting, investment casting, permanent mold casting, and die casting.

This chapter considers various behaviors of microstructural interfaces from a thermodynamics viewpoint. It discusses energy of surface and interface, the Gibbs-Thomson Effect, grain-boundary segregation, smooth and rough interfaces, and grain growth.

This chapter describes various aspects of the billet making process and how they affect the quality of aluminum extrusions. It begins with an overview of the direct-chill continuous casting technique and its advantages over other methods, particularly for hard aluminum alloys. It then discusses the influence of casting variables, including pouring temperature and cooling rate, and operating considerations such as the make-up of charge materials, fluxing and degassing procedures, and grain refining. The chapter also provides information on vertical and horizontal casting systems, billet homogenization, and the cause of casting defects, including cracking and splitting, segregation, porosity, and grain growth.

This chapter describes several macroscopic examination techniques, including macroetching, contact printing, fracturing, and lead exudation. It explains how each method is implemented, why it is used, and what it reveals about manufacturing processes, defects, imperfections, and failure mechanisms.

This chapter reviews failure aspects of structural ferrous powder metallurgy (PM) parts, which form the bulk of the PM industry. The focus is on conventional PM technology of parts in the density range of 6 to 7.2 g/cc. The chapter briefly introduces the processing steps that are essential to understanding failure analysis of PM parts. This is followed by a section on case hardening of PM parts. The methods used for analyzing the failures are then discussed. Some case studies are given that illustrate different failures and the methods of prevention of these failures.

Many of the structural characteristics of steel products are a result of changes that occur during solidification, particularly volume contractions and solute redistribution. This chapter discusses the solidification process and how it affects the quality and behaviors of steel. It explains how steel shrinks as it solidifies, causing issues such as pipe and voids, and how differences in the solubility of solid and liquid steel lead to compositional heterogeneities or segregation. It describes the dendritic nature of solidification, peritectic and eutectic reactions, microporosity, macro- and microsegregation, and hot cracking, as well as the effects of solidification and remelting on castings, ingots, and continuous cast products. It explains how to determine where defects originate in continuous casters and how to control alumina, sulfide, and nitride inclusions.

It is well established that solidification behavior in the fusion zone controls the size and shape of grains, the extent of segregation, and the distribution of inclusions and defects such as porosity and hot cracks. Since the properties and integrity of the weld metal depend on the solidification behavior and the resulting microstructural characteristics, understanding weld pool solidification behavior is essential. This article provides a general introduction of key welding variables including solidification of the weld metal or fusion zone and microstructure of the weld and heat-affected zone. It discusses the effects of welding on microstructure and the causes and remedies of common welding flaws.

Microstructures can be altered intentionally or unintentionally. In some cases, metallographers must diagnose what may have happened to the steel or cast iron based on the microstructural details. This chapter discusses how microstructure in steels and cast irons can be intentionally altered during heat treatment, solidification, and deformation (hot and cold working). Some specific examples are then shown to illustrate what can go wrong through unintentional changes in microstructure, for example, the loss of carbon from the surface of the steel by the process known as decarburization or the buildup of brittle carbides on the grain boundaries of an austenitic stainless steel by the process known as sensitization.

Phases are distinct states of aggregation of matter and one of the primary leverage points for understanding and applying materials. This chapter discusses the phase nature of metals and alloys, the concept of solid solutions, and the use of phase diagrams. It also describes some of the metallurgical effects of freezing or solidification, including the segregation of solutes and the formation of metal glasses.

This chapter describes the basic steps in the production of titanium ingots and their subsequent conversion to standards product forms. It explains how titanium ore is reduced to a spongy residue, then granularized, compacted, and melted (along with alloying additions) to form an ingot, which may be remelted several times to achieve the necessary properties. It also discusses the cause of defects and ingot imperfections and the benefits of billet reduction and grain-refinement processes.

This chapter discusses the melting and conversion of superalloys and the solidification challenges they present. Superalloys have high solute content which can lead to untreatable defects if they solidify too slowly. These defects, called freckles, are highly detrimental to fatigue life. The chapter explains how and why freckles form as well as how they can be prevented. It describes the criteria for selecting the proper melting method for specific alloys based on melt segregation and chemistry requirements. It compares standard processes, including electric arc furnace/argon oxygen decarburization melting, vacuum induction melting, vacuum arc remelting, and electroslag remelting. It also addresses related issues such as consumable remelt quality, control anomalies, melt pool characteristics, and melt-related defects, and includes a section that discusses the processes involved in converting cast ingots into mill products.

This chapter provides an overview of beryllium casting practices and the challenges involved. It discusses the stages of solidification, the effect of cooling rate, the difficulty of heat removal, and the potential for hot cracking. It describes common melting techniques, including vacuum induction melting, vacuum arc melting, and electron beam melting, and some of the ways they have been used to cast beryllium alloys. The chapter also includes information on metal purification and grain refinement procedures.

This chapter discusses the processes, procedures, and equipment used in the production of iron, steel, aluminum, and titanium alloys. It describes the design and operation of melting and refining furnaces, including blast furnaces, basic oxygen and electric arc furnaces, vacuum induction melting furnaces, and electroslag and vacuum arc remelting furnaces. It also covers casting, rolling, and annealing procedures and describes the basic steps in aluminum and titanium production.

This chapter describes some of the more typical manufacturing practices, along with their benefits and limitations. The manufacturing practices covered include primary melting, electroslag remelting, rolling, hot and cold drawing, and continuous casting. The chapter discusses the advance and application of powder metallurgy. A few of the more recently introduced processes that hold considerable promise for producing tool steels or finished tools at a lower cost or with improved quality also are reviewed.

This chapter examines the microstructure of special bar quality (or engineering) steels and how it is influenced by carbon content, tempering temperature, and prior austenitic grain size. It explains how some of the changes are difficult to detect and require special etching and/or measurement techniques. It provides information on many types of engineering steel, including medium and high-carbon steels used in rail applications. It also examines the effect of nickel-phosphorus coatings on stainless steel and phosphate coatings used to reduce friction during thread rolling and other such procedures.

This chapter discusses the practices and procedures used to reveal and record macrostructural features such as hardening depth, weld thickness, crack size, porosity, hot folds, and machining and tooling marks. It provides information on sectioning, sample location, orientation, surface grinding, and etching. It describes macrographic etchants and the features they reveal along with common etching problems and how to avoid them. It explains how to evaluate etching results and how they can be improved using remedial processes such as light grinding. It also discusses photographic reproduction, lighting, and image enhancement techniques.

This article discusses the steps in the primary processing of stainless steels: melting, refining, remelting, casting, and hot rolling. It provides information of the major categories of defects in hot rolled stainless steels, namely hot mill defects, inclusion-related defects, and hot ductility-related defects.

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.