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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.

Alloy 718 forgings have been used extensively in gas turbines for aircraft engines for decades. However their application to land-based power generation gas turbines has been limited to the size of the forgings which can be produced by available forging equipment. GE's recently developed heavy duty gas turbines now require forgings which must be produced from 915 mm diameter ingots which exceed 15,000 kg. The initial hurdle was to melt these large ingots successfully without segregation defects. This was achieved and the results were discussed in a previous conference. This paper describes the unique challenges to converting these ingots into the largest Alloy 718 forgings ever produced. The development work associated with processing these ingots into a uniform fine grain microstructure with the required mechanical properties will be described. The importance of process modeling for developing a process to achieve the structure and property goals will also be discussed.

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The clean metal nucleated casting program is a cooperative research program between GE Energy and Allvac, sponsored by the National Institute of Standards and Technology under the Advanced Technology Program. The goal of the program is to develop a spray-casting technology for the production of extremely large, segregation-free, superalloy ingots for use in turbine wheels in land-based gas turbines. The raw material for the process is a superalloy vacuum induction melted (VIM) electrode; in the CMNC process it is melted in a bottompouring Electro-Slag Remelting (ESR) furnace that forms a stream of liquid superalloy for subsequent atomization and collection in a withdrawal mold. Gas atomization of the stream to form a spray occurs in a chamber where spray distance and gas-to-metal flow rates can be adjusted to cool the metal to a desired level before collection. The approach taken in the R&D program is to address key technical risks associated with the system through construction of a one-ton research plant. These risks include the design and operability of the ESR furnace, pouring system, and collection system. Computational models of all key components of the process are developed and validated against experiments performed on the research plant. The validated models will be used to extrapolate to commercial-sized ingots.