Search Results for metallurgy

This article introduces basic physical metallurgy concepts that may be useful for understanding and interpreting variations in metallographic features and how processing affects microstructure. It presents some basic concepts in structure-property relationships. The article describes the use of equilibrium binary phase diagrams as a tool in the interpretation of microstructures. It reviews an account of the two types of solid-state phase transformations: isothermal and athermal. The article discusses isothermal transformation and continuous cooling transformation diagrams which are useful in determining the conditions for proper heat treatment (solid-state transformation) of metals and alloys. The influence of the mechanisms of phase nucleation and growth on the morphology, size, and distribution of grains and second phases is also described.

This article provides information on the microstructure of powder metal alloys and the special handling requirements of porous materials. It covers selection, sectioning, mounting, grinding, and polishing, and describes procedures, such as washing, liquid removal, and impregnation, meant to preserve pore structures and keep them open for analysis. The article compares and contrasts the microstructures of nearly 50 powder metal alloys, using them to illustrate the effect of consolidation and compaction methods as well as particle size, composition, and shape. It discusses imaging equipment and techniques and provides data on etchants and etching procedures.

This article discusses the fracture and fatigue properties of powder metallurgy (P/M) materials depending on the microstructure. It describes the effects of porosity on the P/M processes relevant to fatigue and fracture resistance. The article details the factors determining fatigue and fracture resistance of P/M materials. It reviews the methods employed to improve fatigue and fracture resistance, including carbonitriding, surface strengthening and sealing treatments, shot-peening, case hardening, repressing and resintering, coining, sizing, and postsintering heat treatments. Safety factors for P/M materials are also detailed.

Powder metallurgy is a near-net shape process capable of producing complex parts with little or no need for secondary operations such as machining, joining, or assembly. However, the inability to produce certain geometrical figures such as transverse holes, undercuts, and threads frequently necessitates some machining, particularly drilling. This article provides a discussion on the measures that can optimize the machining of P/M materials. It reviews the factors influencing machinability of P/M components, including workpiece and tool material properties, cutting conditions, machine and cutting tool parameters as well as some P/M material and production process parameters. These parameters discussed include the particle size, part geometry, porosity, compaction and sintering methods. In addition, the article presents guidelines for the various machining processes, namely, turning and boring, milling, drilling, grinding, reaming, burnishing, tapping, and honing and lapping.

Certain metal products can be produced only by powder metallurgy; among these products are materials whose porosity is controlled. Successful production by powder metallurgy depends on the proper selection and control of process variables: powder characteristics; powder preparation; type of compacting press; design of compacting tools and dies; type of sintering furnace; composition of the sintering atmosphere; choice of production cycle, including sintering time and temperature; and secondary operations and heat treatment. When the application of a powder metallurgy part requires high levels of strength, toughness, or hardness, the mechanical properties can be improved or modified by infiltration, heat treatment, or a secondary mechanical forming operation such as cold re-pressing or powder forging. The article also discusses the effect of the secondary processes on P/M mechanical properties.

This article discusses the classification schemes for cast irons and describes the characteristics of major categories, including gray iron, white iron, ductile iron, compacted graphite iron, mottled iron, malleable iron, and austempered ductile iron. It also discusses some of the basic principles of cast iron metallurgy. When discussing the metallurgy of cast iron, the main factors of influence on the structure include chemical composition, cooling rate, liquid treatment, and heat treatment. In terms of commercial status, cast irons can be classified as common cast irons and special cast irons. Special cast irons differ from the common cast irons mainly in the higher content of alloying elements. Alloying elements can be added in common cast iron to enhance some mechanical properties. They influence both the graphitization potential and the structure and properties of the matrix.

This article provides a detailed discussion on the heat treatment processes for titanium and titanium alloys. These processes are age hardening, solution treatment, aging, and annealing. The article illustrates the characteristics of equilibrium phase diagrams that are important for understanding the heat treatment of titanium alloys. It explains the types of metastable phases encountered in titanium alloys. The article also provides information on the equilibrium phase relationships and properties of titanium alloys.

This article provides information on nickel alloying elements, and the heat treatment processes of various nickel alloys for applications requiring corrosion resistance and/or high-temperature strength. These processes are homogenization, annealing, solution annealing, solution treating, stabilization treatment, age hardening, stress relieving, and stress equalizing. Discussion of furnaces, fixtures, and atmospheres is included. Nickel alloys used for the heat treatment processes include corrosion-resistant nickel alloys, heat-resistant nickel alloys, nickel-beryllium alloys, special-purpose alloys such as nitinol shape memory alloys, low-expansion alloys, electrical-resistance alloys and soft magnetic alloys. Finally, the article focuses on heat treatment modeling for selecting the appropriate heat treatment process.

This article describes the general categories and metallurgy of heat treatable aluminum alloys. It briefly reviews the key impurities and each of the principal alloying elements in aluminum alloys, namely, copper, magnesium, manganese, silicon, zinc, iron, lithium, titanium, boron, zirconium, chromium, vanadium, scandium, nickel, tin, and bismuth. The article discusses the secondary phases in aluminum alloys, namely, nonmetallic inclusions, porosity, primary particles, constituent particles, dispersoids, precipitates, grain and dislocation structure, and crystallographic texture. It also discusses the mechanisms used for strengthening aluminum alloys, including solid-solution hardening, grain-size strengthening, work or strain hardening, and precipitation hardening. The process of precipitation hardening involves solution heat treatment, quenching, and subsequent aging of the as-quenched supersaturated solid solution. The article briefly discusses these processes of precipitation hardening. It also reviews precipitation in various alloy systems, including 2xxx, 6xxx, 7xxx, aluminum-lithium, and Al-Mg-Li systems.

This article focuses on the mechanical properties, production of titanium powder metallurgy (P/M) compacts, namely, blended elemental (BE) compacts and prealloyed (PA) compacts. It explains the postcompaction treatments of titanium P/M compacts, including heat treatment, and thermochemical processing. The article talks about the applications of titanium P/M products, namely, BE and PA products. It concludes with a short note on the future trends in titanium P/M technology.

This article briefly reviews the subject of copper-base powder-metallurgy (P/M) products in terms of powder production methods (atomization, oxide reduction, electrolysis, and hydrometallurgy) and the product properties/consolidation practices of the major applications. Of the four major methods for making copper and copper alloy powders, atomization and oxide reduction are presently practiced on a large scale in North America. The article provides information on the mechanism, production, properties, composition and applications of different types of copper-base P/M products, including self-lubricating sintered bearings, structural parts, oxide-dispersion-strengthened copper, sintered metal friction materials, and porous filters.

This article discusses the applications of high-strength aluminum powder metallurgy (P/M) alloys, detailing the advantages, properties, and the various steps involved in P/M technology, including powder production, powder processing, and degassing and consolidation. Three areas of design efforts to push the inherent advantages of aluminum alloys to new limits are also covered: high ambient-temperature strength with improved corrosion and stress corrosion cracking resistance; improved elevated-temperature properties so aluminum alloys can more effectively compete with titanium alloys; and increased stiffness and/or reduced density for aluminum alloys to compete with organic composites. An appendix provides a detailed account of the properties, processing, and applications of conventionally pressed and sintered aluminum P/M alloys.

Powder metallurgy (PM) processes include press and sinter hardening, metal injection molding, powder forging, hot isostatic pressing, powder rolling, and spray forming. This article provides an overview of PM processing methods and general considerations of heat treatment of PM parts that are case-hardened to obtain higher hardness, wear, fatigue, and impact properties. It describes the effects of porosity on heat treatment, alloy content on PM hardenability, and starting material on homogenization of PM steels. The article describes the properties, following heat treatment, of low-alloy steels tempered at 175 ºC for one hour, and lists recommended quench and temper parameters to achieve good wear resistance and core strength based on different ranges of porosity.

This article focuses on various heat-treating practices, namely, normalizing, annealing, stress relieving, preheating, austenitizing, quenching, tempering, and nitriding for cold-work tool steels. The cold-work tool steels include medium-alloy air-hardening tool steels, high-carbon high-chromium tool steels, and high-vanadium-powder metallurgy tool steels. The article also describes the properties, types, nominal compositions and designations of these cold-work tool steels.

Powder metallurgy (PM) has been called a lost art. Long before furnaces were developed that could approach the melting point of metal, PM principles were used. This article provides an overview of the major historical developments of various methods of platinum powder production. The development of production methods took place in various phases starting from prehistoric time, post-war period, to recent and commercial period. The article discusses the powder metallurgy of platinum, as well as the commercial and post-war developments of PM. Literature and trade associations are also discussed.

The technology to fabricate lower-density, porous powdered metal materials provides unique engineering solutions for many applications. This article summarizes the characteristics and applications of porous powder metallurgy technology, as well as the fabrication methods employed.

This article describes the physical properties of powder metallurgy (PM) stainless steels. These include thermal diffusivity, conductivity, thermal expansion coefficient, Poisson's ratio, and elastic modulus. The article contains a table that lists the characteristics of various grades of PM stainless steels. It discusses the applications of various PM stainless steels such as rearview mirror brackets, anti-lock brake system sensor rings, and automotive exhaust flanges and sensor bosses.

The organizations that are most active in the development of standards for powder metallurgy (PM) are the American Society for Testing and Materials (ASTM), Metal Powder Industries Federation (MPIF), and International Standards Organization (ISO). This article presents the test method standards, materials standards, and material designation codes for PM materials. It provides information on the codes for structural parts, PM soft magnetic materials, PM self-lubricating bearings, metal injection molded materials, and powder forged materials.

This article discusses metal powder processing via hot isostatic pressing (HIP) and HIP cladding when metal powders are being employed in the cladding process. It traces the history of the process and details the equipment, pressing cycle, and densification mechanisms for HIP. The article describes the available process routes for fabricating products using HIP and the steps involved in the production of a part via direct HIP of encapsulated gas-atomized spherical powder. It concludes with information on the microstructures of 316L stainless steel HIP powder metallurgy valve body and a list of the mechanical properties of several powder metallurgy alloys.