Researchers develop a novel alloy for use in aerospace cryogenic applications.

AFRL researchers developed a superhigh- strength aluminum alloy that engineers can use to improve the capability and performance of aerospace components—cryogenic rocket engine components, in particular. They created an aluminum alloy with specific strength and ductility characteristics surpassing those of the alpha titanium alloy currently used in rocket engine turbopumps. The aluminum alloy also demonstrates less sensitivity to hydrogen embrittlement, is lighter weight, and is potentially less costly to manufacture than the titanium alloy.

Engineers expect the new alloy, developed under the guidelines of the Integrated High-Payoff Rocket Propulsion Technology (IHPRPT) program, to reduce the weight and significantly improve the performance of vital spacecraft propulsion components. The IHPRPT program is a coordinated effort between the Department of Defense (DoD), National Aeronautics and Space Administration, and industry to develop—by the year 2010— revolutionary and innovative technologies that will double rocket propulsion capabilities with respect to 1993 state-ofthe- art technology. The program will improve the nation’s capability to move into full-scale development of rocket propulsion systems offering improved performance, affordability, operability, reliability, and maintainability.

Liquid rocket engines use liquid hydrogen (LH₂) as fuel and liquid oxygen (LOX) as an oxidizer; therefore, engine components must function in cryogenic temperatures as low as 20 K (-253°C). The rocket engine’s turbopumps, including the Integrated Powerhead Demonstration (IPD) turbopump, move LH₂ and LOX at high speeds through pipes from cryogenic storage tanks to the rocket’s combustion chamber. The IPD threestage turbopump employs three titanium alloy impellers (see Figure 1). Its progressively higher impeller tip speeds provide higher fuel pressure and, correspondingly, higher engine thrust. However, because these current impellers operate near the strength limit of the titanium alloy, engineers cannot further increase impeller tip speeds. In addition, the titanium alloy impellers are expensive to manufacture and maintain and are prone to hydrogen embrittlement.