Single Residency Sintering and Consolidation of Powder Metal Alloys, Intermetallics, and Composites by Pulsed Homopolar Generator Discharge
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Utilizing inertial energy storage the homopolar generator (HPG) is capable of delivering multimegawatt, megampere current pulses into resistive or inductive loads with high efficiency.(1) Such HPG's have been used for many years as power supplies for research in pulsed processing of metal alloy components and systems. Most of these processes rely on extremely rapid thermal excursions in the workpiece(s) caused by resistive heating during the current pulse. A new application of pulsed HPG's that carries great promise is homopolar pulse consolidation (HPC) of powder metal alloys or components.(2) In HPC, powder metal constituents are loaded into a thermally and electrically insulated die, then precompacted to an initial pressure. The >rams> of the compaction press are also the electrodes for homopolar discharge current. While in single residency, the powder compact is heated uniformly by HPG discharge current, sintering occurs, and consolidation is accomplished by hydraulic control of the consolidation press. The process is completed in approximately one sec, with unaided cooling to room temperature on the order of 100 sec, depending on compact mass. Microstructural control is closely tied to beginning particle size and distribution. Traditionally unsinterable alloys have been consolidated using HPC. Novel intermetallic alloys and phases have been produced. Cermets and other composites can be produced, as long as the continuous matrix is conductive. New tooling designs allow for controlled atmospheres, near-net shapes, and automated manufacturing.