Low Pressure Thermal Deposition of Metal Matrix Composites
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LOW PRESSURE THERMAL DEPOSITION OF METAL MATRIX COMPOSITES T. N. MEYER, J. R. AUHL, A. I. KAHVECI, S. A. JONES AND L. M. ANGERS Aluminum Co. of America, Alcoa Laboratories, Alcoa Center, PA 15069 ABSTRACT The combination of broad materials flexibility and rapid solidification rates achievable during controlled thermal deposition processes provide material designers with exciting new opportunities. Titanium and aluminum alloys have been melted and deposited as dense (90%) sheet and foil products in a controlled low pressure, inert atmosphere chamber. A high frequency (rt) plasma torch is used for a wide range of powder feed sizes. Conversions of powder to deposit have exceeded 90% yields. The deposition chamber accommodates a 1.2 m diameter by 1.2 m wide rotating mandrel. The mandrel drive system and torches are controlled to achieve uniform deposit thickness and effective heat extraction. To produce composite products, the programmable mandrel drive has been coupled with a continuous filament feed system to achieve precise spacing of fiber reinforcements. Initial fiber winding and matrix deposition trials utilized surrogate metal fibers, IN909 and stainless steel, until suitable high strength ceramic fibers became available. The spectrum of materials included metal/metal composites and particulate reinforced matrices. Deposits were characterized with respect to density, composition and metallurgical structure. Aluminum deposits were hot rolled to full density. Preliminary mechanical properties were determined. An overview of Alcoa work to date will be presented and some future composite materials synthesis opportunities will be described. 1. INTRODUCTION As aerospace applications demand lighter and stronger materials with higher temperature capabilities, the "advanced alloys" that meet these requirements typically involve new and challenging barriers to component production. For instance, many intermetallic compounds such as TiAl have generated considerable interest as turbine engine materials but cannot be processed via standard ingot metallurgy routes due to their brittleness at room temperature. Elevated temperature fabrication of these alloys has been stymied by the lack of adequate tooling that is usable at the temperatures where these compounds are ductile. An alternate means of producing sheet and related product forms is low pressure plasma spraying (LPPS), where little post deposition processing is required, being typically limited to a HIP or vacuum hot pressing step for consolidation/densification purposes. In addition, the rapid solidification rates achieved during thermal spraying make these processes especially suited to the production of dispersion strengthened aluminum alloys for elevated temperature applications. Rapid solidification enables the designer to produce alloys containing fine dispersoids from compositions which would normally contain coarse, deleterious, intermetallic particles.[1] Since the dispersion strengthening component is inversely related to the interdispersoid spacing, highest
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