Low Pressure Thermal Deposition of Metal Matrix Composites

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 (rf) 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.