Development of RTI Ti-6Al-2Sn-4Zr-2Mo Production-Scale Fine Grain Size Sheets for Low-Temperature Superplastic Forming Applications

Ti-6Al-4V (Ti-64) and Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) alloy sheets are widely used in monolithic sheet metal aerospace parts fabricated via superplastic forming (SPF), often in combination with diffusion bonding (DB). Conventional Ti-64 sheet is superplastic at temperatures above 1625^oF (885^oC), and conventional Ti-6242 is superplastic at temperatures above 1700°F, above which rapid tool deterioration occurs. Deep alpha case forms that requires removal by expensive and non-environmentally friendly chemical milling. Therefore, reducing SPF temperatures and cycle times are desired for the fabrication of parts via SPF/DB. In recent years, significant effort has been devoted to developing Ti-64 sheet that is superplastic at temperatures in the range 1450-1500^oF (788–816^oC). Aero-engine components currently manufactured from Ti-64 sheet are being converted to Ti-6242 to meet the demands of increased elevated temperature requirements. Consequently, OEMs and Tier 1 suppliers have expressed an interest in Ti-6242 sheet exhibiting “low-temperature” SPF behavior at or below 1550^oF (843^oC). As with Ti-64, lowering the SPF temperature for Ti-6242 will improve die life and eliminate the need for chemical milling. Utilizing modeling tools, RTI developed and validated processing routes for the manufacture of fine grain size sheets of Ti-6242 that exhibit low temperature SPF. This presentation will provide an overview of fine grain size sheet manufacturing developments at RTI for low temperature SPF/DB applications.