The properties of tungsten processed by chemically activated sintering
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I.
INTRODUCTION
A s a refractory metal with the highest melting point, tungsten is technologically attractive and widely used in various fields. Additionally, its high density, small coefficient of thermal expansion, and high temperature mechanical properties are attractive characteristics for certain applications. In general, it is very difficult to fabricate tungsten because of its high melting point, low ductility, and low workability. Even using powder metallurgy (P/M) techniques, processing requires very high sintering temperatures up to 2400 - 2800 °C to get near fully dense tungsten. It is widely recognized that densification is a prerequisite to obtaining high mechanical strength. The addition of small quantities of some transition metals, such as Pd, Pt, Ni, Co, and Fe makes it possible to reduce greatly the sintering temperature of W.1-12 In the past two decades, the work on W activated sintering has progressed to a fairly advanced stage with respect to understanding the mechanism and kinetics of activated sintering. ~3 Based on investigations of Brophy, e t a l . . 2~" 14-19 Schintlmeister and Richter, 2° Samsonov and Yakovlev. ~2°-25 Toth and Lockington, 5 Smith, 26 and German and Munir. 9-u2728 we now have theories which explain the reason for activated sintering, predict the best activator, describe the diffusion rate and path, set the constraints on the process, and provide a kinetic model for the shrinkage. Unfortunately, up to now activated sintering treatments of this type have seen limited use. The lack of mechanical property data and the optimization of strength are major problems. Thus. it is appropriate to study the mechanical response of refractory metal compacts processed by activated sintering to assess potential structural applications. The object of this work was to investigate the effects of the powder characteristics, activators and processing vanables on the shrinkage, and mechanical properties of tungsten compacts processed by activated sintering. The testing has included measurements of shrinkage, density, hardness. and strength of tungsten treated with various activators and CHAOJIN LI, Visiting Scholar from Shanghai Iron and Steel Research Institute, China, and R. M. GERMAN. Associate Professor. are both with Materials Engineering Department. Rensselaer Polytechnic Institute. Troy, NY 12181. Manuscript submitted October 20. 1982. METALLURGICALTRANSACTIONS A
processing variables. Additionally, observations on the fracture surface morphology combined with the above data and metallographic analysis give an understanding to the relationship among composition, processing, structure, and properties. It is reasonable to consider that this kind of study is helpful and necessary for promoting the practical application of activating sintering of tungsten.
II.
EXPERIMENTAL M E T H O D S
Two kinds of well characterized W powder, manufactured by GTE Products Company (Towanda, PA), were selected for this study. Powder characteristics, including chemical purities, are listed in Table I. whil
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