Search Results for porous structures

This chapter is intended to identify materials, processes, and designs that will lead to great advances in powder-binder forming technologies. It discusses some of the structures obtained through these advances in powder-binder technologies such as binder jetting and extrusion-based additive manufacturing, including bound-metal deposition and fused-filament fabrication: oxidation-resistant high-temperature alloys, anisotropic structures, submicrometer-scale structures, surface hard materials, and artist metallic clays. Some of the advances discussed include the developments in process involving plastics, emulsions, ceramics, and porous structures and foams. Improvements in the design processes have led to the development of functional structures, controlled porosity, and bioinspired structures.

The porous structure of powder-metal materials, and thus the sintering method, has a significant impact not only on the properties of PM components, but also on how they respond to surface treatments and fabrication processes such as coating and joining. This chapter explains how the microstructure of PM parts achieved by different sintering methods influences the development of galvanized coatings and the mechanisms involved in sinter bonding and various welding and brazing processes. It presents and interprets the results of several studies in which PM materials, including iron, copper, stainless steel, brass, and bronze alloys, are joined by spot welding, projection welding, and solid-state welding as well as furnace and microwave brazing. It also examines the effects of ZrSiO 4 additions on the friction and wear behaviors of PM bronze brake-lining materials.

This chapter discusses the effects of metallurgical variables on dealloying corrosion. It begins by describing the processes involved in dealloying of metal alloys in aqueous environments. This is followed by a discussion on the morphology of porous dealloyed structures below and above the critical potential. Some features experimentally observed for dealloying systems are then considered. The chapter concludes by briefly reviewing the proposed mechanisms for the formation of porous metals, namely ionization-redeposition mechanism, surface diffusion mechanism, volume diffusion mechanism, and percolation model of selective dissolution.

This chapter provides an introduction to powder processing of binders and polymers. It sets the context for the remainder of the book by providing an overview of the topics discussed in the subsequent chapters and by providing introduction to powder-binder fabrication and customization of feedstock and describing the challenges in component production. The chapter also summarizes alphabetically a few key concepts in powder-binder processing.

This chapter discusses the effect of powder metallurgy on the design and production of nuclear energy reactors, wind turbines, biomedical devices, and gas turbine engines.

This chapter explains how powder metallurgy technologies are being leveraged for the production of automotive components, electric motors, rare-earth permanent magnets, and the infrastructure for high-speed rail transport.

This chapter discusses the growing use of sintered stainless steels in automotive applications and various types of filters and filtering media. It also describes how these materials are produced in the form of metal foams and cellular structures and how they serve as flake pigments in corrosion-resistant coatings.

The conversion of feedstock into a shape involves the application of heat and pressure, and possibly solvents. This chapter discusses the operating principle, advantages, limitations, and applications of such shaping processes, namely additive manufacturing, cold isostatic pressing, die compaction, extrusion, injection molding, slip casting, slurry processes, and tape casting. Information on equipment setup, requirements, and the various factors influencing these processes are described. In addition, the chapter provides information on novel approaches and processing costs applicable to these shaping processes.

This chapter covers the basic steps of the powder metallurgy process, including powder manufacture, powder blending, compacting, and sintering. It identifies important powder characteristics such as particle size, size distribution, particle shape, and purity. It compares and contrasts mechanical, chemical, electrochemical, and atomizing processes used in powder production, discusses powder treatments, and describes consolidation techniques along with secondary operations used to obtain special properties or improve dimensional precision. It also discusses common defects such as ejection cracks, density variations, and microlaminations.

Casting is the most economical processing route for producing titanium parts, and unlike most metals, the properties of cast titanium are on par with those of wrought. This chapter covers titanium melting and casting practices -- including vacuum arc remelting, consumable electrode arc melting, electron beam hearth melting, rammed graphite mold casting, sand casting, investment casting, hot isostatic pressing, weld repair, and heat treatment -- along with related equipment, process challenges, and achievable properties and microstructures. It also explains how titanium parts are produced from powders and how the different methods compare with each other and with conventional production techniques. The methods covered include powder injection molding, spray forming, additive manufacturing, blended elemental processing, and rapid solidification.

This chapter discusses the use of thermoset and thermoplastic resins in polymer matrix composites. It begins by explaining how the two classes of polymer differ and how it impacts their use as matrix materials. It then goes on to describe the characteristics of polyester, vinyl ester, epoxy, bismaleimide, cyanate ester, polyimide, and phenolic resins and various toughening methods. The chapter also covers thermoplastic matrix materials and product forms and provides an introduction to the physiochemical tests used to characterize resins and cured laminates.

Thermal barrier coatings (TBCs) are applied using thermal spray coating (TSC) processes to components that are internally cooled and operated in a heated environment. The TSC microstructures are prone to interactions with common metallographic procedures that may result in artifacts and misinterpretation of the TSC microstructure. This article aims to aid in identifying metallographic TSC artifacts, specifically in the air plasma spray zirconia-based TBC, including both of its common constituents, the bond coating and the top coating. Artifacts that result from specific sectioning and mounting practices, as well as from different polishing times, are presented. Additionally, the article discusses the factors in optical microscopy and scanning electron microscopy that affect microstructure interpretation.

This chapter discusses the advantages and disadvantages of sandwich and integral cocured structures, and the methods by which they are made. It begins by explaining where and how sandwich construction is used and why it is so efficient. It then describes the design and fabrication of honeycomb panels and foam cores along with their respective applications and unique attributes. The chapter also discusses the cocuring process and its use in fabricating unitized structures.

This chapter discusses the advantages and limitations of 3D printing technology for the production of batteries and supercapacitors. It explains how 3D printing methods facilitate the build of microdevices with hierarchical nanoarchitectures and controlled microstructure. It also reviews recent progress in fabricating electrodes and electrolytes using 3D-printed functional materials.

This chapter recounts some of the early efforts and milestones in the development of stainless steel powders and their use in powder metallurgy applications.

This article summarizes the results of work completed by the ASM Thermal Spray Society Advisory Committee to identify key research challenges and opportunities in the thermal spray field. It describes and prioritizes research priorities related to emerging process methods, thermal spray markets and applications, and process robustness, reliability, and economics.