This article addresses the cobalt and cobalt-base alloys most suited for aqueous environments and those suited for high temperatures. The performance of cobalt alloys in aqueous environments encountered in commercial applications is discussed. The article provides information on the environmental cracking resistance of the cobalt alloys. Three welding processes that are used for hardfacing with the high-carbon Co-Cr-W alloys, namely, oxyacetylene, gas tungsten arc, and plasma-transferred arc are also discussed. The article examines the effects of various modes of high-temperature corrosion. It describes the applications and fabrication of cobalt alloys for high-temperature service.

Cobalt is used as an alloying element in alloys for various applications. This article provides a detailed account of the metallurgy of cobalt-base alloys. It focuses on the compositions, properties, and applications of cobalt-base alloys, which include wear-resistant cobalt alloys, heat-resistant cobalt alloys, and cobalt-base corrosion-resistant alloys. The article also describes the heat treatments such as annealing and aging, for these alloys.

This article reviews some concepts considered important for an understanding of processes used for preparing cobalt-chromium alloy implants, the microstructures resulting from this processing, and the resulting material properties. The review includes the solidification of alloys, diffusionless (martensitic) phase transformation as occurs with face-centered cubic to hexagonal close-packed transformation in cobalt-chromium alloys, stacking faults and twins and their role in this transformation. It also includes strengthening mechanisms that are responsible for the mechanical properties of cast and wrought cobalt alloys. The article contains tables that list the commonly used cobalt alloys and their biomedical applications and chemical compositions. It discusses the mechanical and corrosion properties of cobalt alloys, and provides a description of the microstructure of cobalt alloys.

This article provides a discussion on forging methods, melting procedures, forging equipment, forging practices, grain refinement, and critical factors considered in forging process. It describes the different types of solid-solution-strengthened and precipitation-strengthened superalloys, namely, iron-nickel superalloys, nickel-base alloys, cobalt-base alloys, and powder alloys. The article discusses the microstructural mechanisms during hot deformation and presents processing maps for various superalloys. It concludes with a discussion on heat treatment of wrought heat-resistant alloy forgings.

This article describes the methods for removing metallic contaminants, tarnish, and scale resulting from hot-working or heat-treating operations on nickel-, cobalt-, and iron-base heat-resistant alloys. It provides a brief description of applicable finishing and coating processes, including polishing, electroplating, ceramic coatings, diffusion coatings, and shot-peening. The article presents numerous examples that identify cleaning and finishing problems and the procedures used to solve them.

Heat treating of stainless steel produces changes in physical condition, mechanical properties, and residual stress level and restores maximum corrosion resistance when that property has been adversely affected by previous fabrication or heating. This article focuses on annealing of different types of stainless steels such as austenitic, ferritic, duplex, martensitic, and precipitation-hardening, and on the heat treatment of superalloys and refractory metals. It discusses the recommended procedures for solution annealing, austenite conditioning, transformation cooling, and age tempering of precipitation-hardening stainless steels. The article also lists general recommendations for the annealing temperatures of tantalum, niobium, molybdenum, tungsten, and their alloys.

Although stainless steel is naturally passivated by exposure to air and other oxidizers, additional surface treatments are needed to prevent corrosion. Passivation, pickling, electropolishing, and mechanical cleaning are important surface treatments for the successful performance of stainless steel. This article describes the surface treatment of stainless steels including abrasive blast cleaning, acid pickling, salt bath descaling, passivation treatments, electropolishing, and the necessary coating processes involved. It also describes the surface treatment of heat-resistant alloys including metallic contaminant removal, tarnish removal, oxide and scale removal, finishing, and coating processes.

This article describes the applications, advantages, and disadvantages of three centrifugal casting processes as well as the equipment used. The processes include true centrifugal casting (horizontal, vertical, or inclined) semicentrifugal (centrifugal mold) casting, and centrifuge mold (centrifugal die) casting. The article discusses the cooling, inoculation, fluxing, and extraction of casting. It reviews mold heating and coating techniques as well as various molds used for the centrifugal casting processes. The three most common defects observed in centrifugal castings are also discussed. The article concludes with information on the applications of centrifugal force in investment casting and combustion synthesis.

Superalloys are nickel, iron-nickel, and cobalt-base alloys generally used for high-temperature applications. Superalloys are used in aircraft, industrial, marine gas turbines, nuclear reactors, spacecraft structures, petrochemical production, orthopedic and dental prostheses, and environmental protection applications. This article discusses the material characteristics, phases, structures, and systems of superalloys. It describes the processing of superalloys, including primary and secondary melting, deformation processing (conversion), powder processing, investment casting, and joining methods. The article also describes the properties, microstructure, and thermal exposure of superalloys. It further discusses the effects of environmental factors on superalloys, including oxidation and hot corrosion. Protective coatings are also discussed. The article provides information on the mechanical properties and chemical composition of nickel, iron, and cobalt-base superalloys in both the cast and wrought forms.

This article reviews the pattern materials used in investment casting. It describes patternmaking process, pattern tooling, and pattern and cluster assembly. The article provides information on melting equipment, casting methods, and the inspection and testing of investment casted materials. It presents recommendations that which serve as a useful guide to the design of investment castings. The article tabulates the applications of the process and illustrates the Shellvest system for investment casting of small parts. It explains the manufacturing process of ceramic shell molds and cores. Binders and materials used for ceramic shell molds; slurry and cluster formulation; and pattern removal methods in the manufacturing process are summarized. The article discusses the coating and drying process of clusters and slurries.

This article provides a discussion on ten rules for the effective production of reliable castings. The rules include good-quality melt, liquid front damage, liquid front stop, bubble damage, core blows, shrinkage damage, convection damage, segregation, residual stress, and location points.

In terms of component design, casting offers a great amount of flexibility. This article discusses the parameters that can drive the geometry of casting design from a process standpoint. It provides information on the design of junctions and addresses considerations of secondary operations in design. The article describes the factors that control casting tolerances and provides specific tips for designing castings with uniform wall thickness and unequal sections, designing thin sections, designing for economical coring, designing for functional packaging, and core design principles. The choice of whether a component is best manufactured as welded, assembled, fabricated, forged, machined, or cast is based on the component geometry, production costs, and requirements in application. The article addresses these issues and provides a framework for analyzing all manners of manufacturing as possible conversion candidates. It concludes with a discussion on different metalcasting design projects.

Sand mold and permanent mold castings are the major methods for shape casting of steels, with production closely split among green sand, chemically bonded sand, and permanent mold processes. This article describes the steel solidification characteristics, melting practices, melt treatment, and feeding of the molten steel into the mold used in steel foundries. It discusses the features of the melting furnaces used in direct arc melting, induction melting, and boiling. The article describes the sand casting and permanent mold casting of steel. The process design and castings of thin sections are also discussed.

Batch furnaces and continuous furnaces are commonly used in heat treating. This article provides a detailed account of various heat treating equipment and its furnace types, including salt bath equipment (externally heated, immersed-electrode and submerged-electrode furnaces), and fluidized-bed equipment (external-resistance-heated fluidized beds). It describes various auxiliary equipment used in cold-wall furnaces, namely, heating elements and pumping systems. Five types of heat-resistant alloys are used for furnace parts, trays, and fixtures: Fe-Cr alloys, Fe-Cr-Ni alloys, Fe-Ni-Cr alloys, nickel-base alloys and cobalt-base alloys. The article lists the recommended applications for alloys for parts and fixtures for various types of heat treating furnaces.

Hardfacing is defined as the application of a wear-resistant material, in depth, to the vulnerable surfaces of a component by a weld overlay or thermal spray process Hardfacing materials include a wide variety of alloys, carbides, and combinations of these materials. Iron-base hardfacing alloys can be divided into pearlitic steels, austenitic (manganese) steels, martensitic steels, high-alloy irons, and austenitic stainless steel. The types of nonferrous hardfacing alloys include cobalt-base/carbide-type alloys, laves phase alloys, nickel-base/boride-type alloys, and bronze type alloys. Hardfacing applications for wear control vary widely, ranging from very severe abrasive wear service, such as rock crushing and pulverizing to applications to minimize metal-to-metal wear. This article discusses the types of hardfacing alloys, namely iron-base alloys, nonferrous alloys, and tungsten carbides, and their applications and advantages.

This article reviews specific processing characteristics and forging-related properties of commonly forged families of metals and alloys, including carbon and alloy steels, stainless steels, heat-resistant alloys (iron, cobalt, and nickel base alloys), aluminum alloys, copper and copper alloys, magnesium alloys, and titanium alloys. It provides forging process variables such as stock preparation, heating and cooling of forgings, die lubrication, trimming, and cleaning of these metals and alloys. The article explains the effect of temperature, deformation rate, and die temperature on forgeability and describes the forging methods of these metals and alloys.

Nickel-base alloy castings are widely used in corrosive-media and high-temperature applications. This article begins with a discussion on the compositions of corrosion-resistant nickel-base casting alloys and heat-resistant nickel-base casting alloys. It describes the effects of aluminum and titanium on the structure and properties of nickel-base alloys. The article provides information on the melting, foundry, and pouring practices for nickel-base alloys. It describes the welding and heat treatment of the nickel-base casting alloys. The article concludes with information on the numerous applications of cast heat-resistant nickel-base alloys.

Cast nickel-base alloys are used extensively in corrosive-media and high-temperature applications. This article briefly reviews the common types of heat treatments of nickel alloy castings: homogenization, stress relieving, in-process annealing, full annealing, solution annealing, quenching, coating diffusion, and precipitation. It describes the three general strengthening mechanisms, namely, solid-solution hardening, age hardening, and carbide precipitation. The article summarizes the typical heat treatment of the general families of nickel-base castings used in industrial applications. It focuses on the solution treatment and age hardening of cast nickel-base superalloys and the heat treatment of cast solid-solution alloys for corrosion-resisting applications. The article also discusses the typical types of atmospheres used in annealing or solution treating: exothermic, endothermic, dry hydrogen, dry argon, and vacuum.

This article focuses on the analysis of materials and mechanical- (or biomechanical-) based medical device failures. It reviews the failure analysis practices, including evidence receipt, cleaning, nondestructive examination, destructive examination, exemplars analysis, and device redesign. The article examines the common failure modes, such as overload, fatigue, corrosion, hydrogen embrittlement, and fretting, of medical devices. The failure analysis of orthopedic implants, such as permanent prostheses and internal fixation devices, is described. The article reviews the failure mechanisms in some of the more common medical device materials, namely, stainless steels, titanium alloys, cobalt-base alloys, and nitinol. It presents case histories with examples for failure analysis.

Cast stainless steels are widely used for their corrosion resistance in aqueous media at or near room temperature and for service in hot gases and liquids at elevated temperatures. This article provides a comparison between cast and wrought stainless steels in terms of composition, microstructure and properties. It discusses the grade designations and compositions of cast stainless steels. The article describes the mechanical properties, applications, and corrosion characteristics of corrosion-resistant steel castings and heat-resistant steel castings.