Consolidation methods for spherical rhenium and rhenium alloys

Abstract

The development of high density spherical rhenium and spherical tungsten-rhenium powders has enabled the use of advanced consolidation techniques for the manufacture of refractory metal components. The investigated consolidation techniques are powder metal injection moulding (PIM) and vacuum plasma spraying (VPS); both produce net shape components. The required particle size distributions for these applications vary. VPS uses a large powder particle size (<44 μm) while PIM requires a fine particle size (<20 μm). The major advantages of spherical powders over traditional powders in plasma spraying are the high density of the powder particles and its good flow characteristics. These two factors combine to produce high density sprayed formed parts. PIM requires that the powder particles be dense as well as fine. Powder particles must be small enough to be entrapped in the binder but without being so small (<0·5 μm) that the body forces dominate. Binders for PIM are tailored to the powder's characteristics, including size, distribution, shape and reactivity. Binder systems are developed to provide maximum packing powder, while maintaining the ability to be moulded, and to allow debinding without chemically reacting with the powder. A discussion of the powder production process and the general characteristics of spherical refractory powders, as well as the alloys produced to date, will be discussed. Further, both consolidation techniques will be discussed in depth, focusing on the role the powder's attributes play in each technique. Spherical rhenium and spherical tungsten-rhenium powders are presently being used in non-erosion throats and other propulsion system applications.