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I.

INTRODUCTION

Powder metallurgy (P/M) is a technique in which fine metal particles, typically less than 100 mm in dimension, are used as feed stock in the production of high-quality, low cost, or otherwise unique components. Advanced forming techniques, in conjunction with small particle size, have made nonequilibrium microstructures such as glassy, nanoand microcrystalline metals attainable. Premixed and prealloyed powders can be used to exert control over a product’s final compositional and microstructural characteristics, thus avoiding problems such as coarse, dendritic second-phase segregation. The P/M technique has proven to be effective in the production of specialty items for nuclear, aerospace, electrical, and magnetic applications.[1–4] Mechanical, electrical, and magnetic properties of engineering components can all be traced back to the microstructural characteristics of the component. Although compaction and sintering mechanisms are critical to the manufacture of fully dense, near-net shape parts,[5,6,7] the performance of the final product may be limited by the material properties of the individual particles. A part fabricated by advanced P/M methods will possess a level of microstructural integrity comparable to the powder from which it was formed. Thus, it is important to examine the microstructure of the individual particles for point, line, and planar defects and features such as porosity, inclusions, B.I. PRENITZER, Graduate Research Assistant, and L.A. GIANNUZZI, Associate Professor, are with the Department of Mechanical, Materials, and Aerospace Engineering, University of Central Florida, Orlando, FL 32816-2450. K. NEWMAN is Manager of Process Development, Keystone Powdered Metal Company, St. Marys, PA 15857. S.R. BROWN, Senior Technical Associate, and R.B. IRWIN and F.A. STEVIE, Members of the Technical Staff, are with Cirent Semiconductor, Orlando, FL 32819. T.L. SHOFNER, Senior Technical Associate, formerly with Kirk Resources, Orlando, FL 32819, is with The Bartech Group, Orlando, FL 32819. Manuscript submitted January 15, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS A

cracking, and segregation. Light optical microscopy (LOM) and scanning electron microscopy (SEM) are useful for observing macroscopic defects. In some cases, SEM can also be used to determine grain boundary structure and orientation relationships; however, transmission electron microscopy (TEM) is the preferred technique for performing detailed microstructural evaluation and defect analysis. A TEM specimen should be representative of and unchanged from the bulk microstructure. If the microstructure is modified during specimen preparation, then those changes should be well characterized. A typical TEM specimen is 3 mm in diameter having electron transparent regions on the order of a few mm wide by ;100 nm in thickness. The dimensional requirements alone are enough to ensure that the preparation of TEM specimens by conventional methods will be nontrivial. The TEM specimen preparation becomes more rigorous when the sample