Powder metallurgy (PM) is a versatile and multifaceted technology. Most commonly, it is used to produce complex structural components with superior dimensional accuracy and good mechanical properties in a cost-effective manner. Apart from this, it is the only way possible to produce some highly specialized material, such as cermets, hard metals, and metallic filters. It is also used to produce improved versions of high-performance alloys (tool steels, magnetic alloys, and composite materials) by ensuring superior control of microstructure and purity. In terms of tons produced, the PM industry is still considered small with only 1% by weight of all metals sold in the industry, but in terms of dollar value, due to its unique capabilities, its use is growing at a faster rate than average.
In 1984, the first ASM Handbook Volume devoted entirely to PM was published in recognition of the increasing acceptance of PM as a viable manufacturing technology. A revised edition published in 1998 captured significant advancements made in the interim. Both of these Volumes have served the PM community well. Technological advancements continue to be made in all facets of PM as more and more new applications come on board and also as the traditional applications are challenged to deliver greater performance and economy. The technology is growing both in its breadth and depth. During the planning of the current edition, it was felt that it would not be feasible to cover all facets of PM technology in one Volume. It was also felt that the practicing PM industry professional generally has different needs than researchers and academicians. In view of this, it was decided to focus this Volume primarily on the traditional press-and-sinter PM technology. The more advanced techniques and emerging technologies, such as additive manufacturing, are deferred to other potential Volumes. A notable exception to this premise is the inclusion of metal injection molding (MIM) in this Volume, which is presented as a distinct division.
Material properties achieved with PM processing can vary widely depending on the process parameters used as well as the starting raw material. To achieve optimal properties for a given application, one must have full understanding of the effects of process variables on the microstructure and macrostructure of the component (including density), which, in turn, will influence its physical and mechanical properties. The process engineer must balance process complexity and the costs associated with it against the resulting material properties, as well as the dimensional requirements. The process-property relationships can vary to a large extent from one metal/alloy family to another. The revised Volume's format is aimed at simplifying the understanding of process-property relationships by treating each metal/alloy family in individual divisions.
The Volume is organized in two parts. The first part (following an introductory division on history and material standards) covers the basic principles and techniques that are common to all PM materials. These divisions include powder manufacture, powder characterization, compaction, sintering, and full density processing. The information provided in these divisions is sufficient for developing a basic understanding of the subject. For additional information, the reader is encouraged to refer to textbooks devoted to these subjects. The second part covers detailed information on PM technology as it applies to individual metal/alloy families, by presenting each metal/alloy family in a separate division. Within each material-specific division, the information presented follows the typical production steps: powder manufacture, compaction, sintering, secondary processing, as well as properties and applications. Major emphasis is placed on the material and processes as they are currently used in industry. All MIM-produced materials are covered under the division on metal injection molding, so as to avoid any confusion with property comparison with materials produced by traditional PM processing.
The Volume is designed to serve as a reference book for PM professionals—process engineers, development engineers, production managers, as well as the sales and marketing personnel. The updated material properties data presented in this Volume will also be helpful to the design engineer and assist him or her in specifying PM components in new applications. The Volume bridges the gap between standard textbooks and research papers presented at technical conferences. The presentation of information is such that it can be used as an introduction to powder metallurgy by the new workforce entering the field.
We would like to offer our sincere thanks to the contributing authors, most of whom worked on their own time to prepare the articles that make up this Volume. This extensively reorganized edition would not have been possible without the dedicated efforts of the division editors. Special thanks are due to the ASM Handbook Committee as well as Steven Lampman, Content Developer and ASM Handbook Committee Staff Liaison of ASM, for their vision and guidance. The cooperation and assistance of the Metal Powder Industries Federation and its sister organization, American Powder Metallurgy Institute, are greatly appreciated.
Much appreciation goes to Ms. Vicki Burt, Content Developer, for organizing and coordinating the entire project. Also, to the editorial staff of ASM for editing the submitted material; all of their work on this Volume was invaluable.
Prasan K. Samal
Joseph W. Newkirk