TITANIUM METAL MATRIX COMPOSITES FOR AEROSPACE APPLICATIONS S. A. Singerman* and J. J. Jackson** *Pratt &Whitney West Palm Beach FL **GE Aircraft Engines

Aerospace engine and airframe designers are constantly seeking lighter weight high strength materials to reduce weight and improve performance of powerplants and aircraft. Titanium metal matrix composites (Ti MMCs) have offered the promise of significant weight savings since their initial development in the early 1960s but until recently, their inadequate quality and reproducibility combined with high processing and materials costs have prevented their introduction into production applications. This paper describes the state-of-the-art for Ti MMC aerospace fabrications, their potential payoffs and the recent advances in processing which are now leading to high quality, affordable Ti MMC components. Introduction & Historical Persnective Over the past 30 years, titanium metal matrix composites (Ti MMCs) have been under considerable development and evaluation for use in aircraft engine and airframe applications. For airframers, the high specific modulus of Ti MMCs has been the impetus,(i-3) while engine makers have sought to take advantage of their high specific strength, especially for compressor rotor applications.(4) With the development of titanium aluminide matrix alloys(5r6) which have temperature capabilities approaching 760°C (1400°F) Ti MMCs offer a potential 50% weight reduction in the hotter compressor sections now dominated by nickel based superalloys. The introduction of Ti MMCs into high performance engine applications has been inhibited partly by the complexities of composite rotor fabrication. However, a more significant barrier is their high materials and implementation cost(T) which is mainly driven by low market volume. To overcome these barriers, Ti MMC components with higher volume applications are now being emphasized by Pratt & Whitney (P&W) and GE Aircraft Engines (GEAE) under the Advanced Research Projects Agency (ARPA)/Air Force sponsored Titanium Matrix Composite Turbine Engine Component Consortium (TMCTECC) Program.(*) The high bypass commercial turbofan engines which will power long range aircraft into the next century can benefit greatly from the weight and operating cost reductions enabled by the selective use of Ti MMCs in their structures. These applications represent the size market needed to make Ti MMCs cost competitive (Ti MMCs at $1100 per kilogram, $500 per pound) for production introduction into engines or airframes.(s) The following describes the status of Ti MMCs in terms of their demonstrated capabilities, potential payoffs and progress towards achieving affordable manufacture of components for aerospace applications. Processing & Properties Ti MMCs which have demonstrated properties suitable for aerospace applications consist of conventional (Ti6A14V, Ti6A12Sn4Zr2Mo. etc.) and advanced (Ti3A1, TiAl, etc.) titanium matrix alloys reinforced with 30-40 volume percent of continuous arrays of high strength (>3450 Mpa, ~500 ksi), high modulus (380 Gpa, 55 msi) SIC ftbers.$ These fibers are approximately 0.127 mm (5 mils) in diameter and produced by chemical vapor deposition (CVD) with a 4 pm (0.2 mil) carbon rich surface layer to enhance processability, fiber strength and achieve desired metal/fiber interface characteristics.(“,t(‘)