Super-high strength Al-Zn-Mg-Cu alloys with Sc and Zr additions have recently been developed by UES, Inc. on request of the US Air Force for a liquid hydrogen turbopump impeller (SBIR Phases I and II, 2001-2005, Air Force Contracts F04611-01-C-0030, F04611-02-C-0014). These alloys have superior cryogenic mechanical properties in cast, forged and extruded conditions. For example, in the temperature range from 4K to 300K, the specific tensile strength of some of these alloys exceeds the specific strength of Ti-5Al-2.5Sn; the latter alloy is currently used for this application. Replacement of the Ti alloy impeller with the super-high strength Al alloy impeller would be beneficial for an increase in engine performance, decrease in weight, and decrease in overall cost.

The objective of the SBIR Phase II Enhancement program, which started in June 2005 is to generate the mechanical and physical property data for a selected developmental super-high strength Al alloy. This data is necessary to conduct preliminary turbopump design analyses. Several full-scale impeller preforms have already been produced from the developmental Al alloy using advanced thermomechanical and heat treatment processes developed and optimized during the Phase II program. Samples will be extracted from critical sections of these preforms and mechanical tests will be conducted at two cryogenic temperatures (T = 4K and 77K) and room temperature (298K) according to ASTM or other applicable standards to include, but not limited to: tensile properties of regular and notched specimens, high cycle fatigue, fracture toughness, and elastic moduli. Physical properties such as density, coefficient of thermal expansion, and coefficient of thermal conductivity will also be determined in the operational temperature range. Based on the generated data, an impeller prototype will be produced and subjected to a spin test in a fuel turbopump environment to insure that established properties are fulfilled. The work is being conducted in collaboration with Pratt & Whitney Rocketdyne Propulsion and Power (subcontract). The period of performance of this program is 15 months.

Additional details of this program can be obtained from Dr. Oleg Senkov
(937-255-1320, E-Mail: Oleg.Senkov@wpafb.af.mil).