R&D on Composition and Processing of Titanium Aluminide Alloys for Turbine Engines
Interim rept. Oct 1980-Jan 1982
PRATT AND WHITNEY WEST PALM BEACH FL GOVERNMENT PRODUCTS DIV
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In this current program, one alpha-two and several gamma compositions were selected, produced as large ingots and isothermally forged. Extensive mechanical property testing was conducted on these forgings. In addition, various material processing methods such as casting, rolling, extrusion and machining were evaluated. The alpha-two alloy Ti-25Al-10Nb-3V-1Mo exhibited the best balance of tensile and stress-rupture properties found to date and had a higher elastic modulus. Beta grain size was shown to have major effects on creep, low cycle fatigue and fracture toughness. Alloy stability, as measured by post-exposure tensile ductility, was poor and was tentatively traced to precipitation of an unidentified phase in the beta. Heat treatment modifications were suggested to alleviate this problem. Processing studies showed that many of the methods developed for forging, joining and rolling of conventional titanium alloys can be applied to the alpha-two alloys. Screening tests conducted on four gamma alloys did not identify an alloy with a better property balance than Ti- 48Al-1V-.1C which had been evaluated previously. Properties were more consistent with previous small scale ingots, although ductility and impact strength were somewhat lower, and quite good toughness levels were measured. Alloy stability was excellent after exposure and processing studies established machining procedures and demonstrated and demonstrated that the alloy has fair castability.
- Properties of Metals and Alloys
- Fabrication Metallurgy