Advanced Aluminum Materials for Rocket Turbopump Rotors

The objective of the proposed program is to identify and develop aluminum based material that can replace the currently used Ti-5Al-2.5Sn ELI alloy as a liquid hydrogen pump impeller operating at 20¿K. This application requires very high specific strengthas well as adequate toughness and resistance to hydrogen embrittlement. Aluminum alloys are of particular interest because in comparison with titanium, their density is much lower, they are less expensive, can be processed and machined much easier, andthey have very low susceptibility to hydrogen embrittlement. However, the currently available aluminum alloys cannot compete with titanium alloys because of low specific strength. During Phase I the mechanical properties of a conventional aluminum alloy(7XXX series) will be considerably improved through microalloying with Sc and Zr followed by special thermomechanical processing. The strength of the modified alloy will be increased to values equal to or exceeding 950 MPa at 20¿K, with elongation of about7%. The fact that a commercial Al alloy is selected will cut down significantly on development cycle costs. Development of this ultra-high strength aluminum alloy will help designers to improve engine performance by decreasing weight of rotor components,increasing impeller tip speed, and reducing complexity and cost.Development of super-high-strength Al-based material with good fatigue resistance will offer designers a real potential to improve the turbopump performance by decreasing the weight of rotorcomponents, increasing impeller tip speed, and significantly reducing complexity and cost. Current titanium impellers such as those used on the Space Shuttle Main Engine (SSME) require complex, high-maintenance, polymeric seals because of concerns aboutmetal-to-metal contact and titanium hydriding. The super-high-strength aluminum will eliminate this concern, simplifying seal design and improving seal life and reliability. This alloy will also find widespread use in the commercial aerospace andtransportation sectors. Because higher specific strengths translate directly into reduced component mass without redesign, super-high-strength Al-based alloys will be attractive in any application where component mass and/or volume are constrained, e.g.orbital applications including, but not limited to: bus structures, truss nodes, brackets, hinges, radiator panels and PCB heat sinks. The alloy will also have a significant impact in sustainment, since direct component-for-component replacement will givehigher performance in existing systems, e.g. extended component life and reduced maintenance for F-16 aircraft ventral fins. Additional impact will also be felt in the area of unitized design and construction, insofar as increased performance can be met atreduced cost through reducing numbers of parts and fasteners.