Abstract
The attractive combination of strength and low density has resulted in titanium alloys covering 15 to 25% of the weight of a modern jet engine, with titanium currently being used in fan, compressor and nozzle components. Typically, titanium alloys used in jet engine applications are selected from the group of near alpha and alpha-beta titanium alloys, which exhibit superior elevated temperature strength, creep resistance and fatigue life compared to typical titanium alloys such as Ti-6Al-4V. Legacy titanium alloys for elevated temperature jet engine applications include Ti-5Al-2Sn-2Zr-4Mo-4Cr, Ti-6Al-2Sn-4Zr-2Mo-0.1Si and Ti-4Al-4Mo-2Sn-0.5Si. Improving the mechanical behavior of these alloys enables improved component performance, which is crucial to advancing jet engine performance. As a world leader in supplying advanced alloys of titanium, nickel, cobalt, and specialty stainless steels, ATI is developing new titanium alloys with improved elevated temperature properties. These improved properties derive from precipitation of secondary intermetallics in alpha-beta titanium alloys. ATI has developed several new alpha-beta titanium alloy compositions which exhibit significantly improved elevated temperature strength and creep resistance. This paper will focus on the effects of chemistry and heat treat conditions on the microstructure and resulting elevated temperature properties of these new aerospace titanium alloys.
Highlights
For decades Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-6242Si, UNS R54620) has been the workhorse alloy for high temperature aerospace applications due to its excellent elevated temperature strength, creep resistance and good weldability
Room and elevated temperature tensile properties were consistent between the three experimental heats (Figure 6)
Elevated temperature creep resistance improved as a function of increasing germanium content; both in total strain at 125 hours and in steady state creep rate (Figure 6)
Summary
For decades Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-6242Si, UNS R54620) has been the workhorse alloy for high temperature aerospace applications due to its excellent elevated temperature strength, creep resistance and good weldability. Higher temperature resistant alpha-beta alloys such as ATI 6-2-4-2TM alloy requires high volume fraction of alpha phase, so they contain higher amounts of alpha stabilizers such as Al, Sn, and Zr. On the other hand, beta alloys such ATI 21STM alloy and ATI 15MoTM alloy contain higher amount of beta stabilizers such as Mo, Nb or V and lower amount of alpha stabilizers such as Al, Zr, or Sn. Figure 1 shows aerospace titanium alloys commonly produced at ATI categorized in terms of Aleq and Moeq. Most high-temperature titanium alloys take advantage of heat treatment to precipitate strengthening secondary alpha phase, and are between 5 < Aleq < 9 and 1 < Moeq < 10
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