A. B. Pandey, Pratt & Whitney Rocketdyne, West Palm Beach, FL; J. E. Spowart, Air Force Research Laboratory, Wright-Patterson AFB, OH
There has been growing interest to develop high strength and high temperature aluminum alloys to reduce weight of high performance aerospace and space components. Typically, aerospace and space components are made out of nickel base superalloys and steels. The use of a high strength and high temperature aluminum alloy can reduce the weight of components providing a substantial increase in the system’s thrust-to-weight ratio. New aluminum alloys containing nanocrystalline L12 strengthening precipitate are being developed under a program funded by the Air Force Research Laboratory. Process development and scale up of L12 strengthened aluminum alloys are also being performed under an IR&D program. The present aluminum alloy is based on a novel Al-Sc based alloy system. Aluminum-scandium alloy forms Al3Sc based precipitate that has an L12 structure which is strong and thermally stable up to very high temperatures. The strength and thermal stability of Al3Sc precipitate can further be improved by additional elements. These dispersoids provide strengthening in the alloy through Orowan strengthening, antiphase boundary energy strengthening and grain size strengthening. The proposed P/M alloy has demonstrated very high strength for a range of temperatures up to 600°F. Process parameters have been optimized to produce optimal properties in the material. These alloys have demonstrated an excellent compatibility with high pressure gaseous hydrogen. High cycle fatigue and creep tests of these alloys were also conducted. Fatigue results of these alloys showed good endurance limits at room temperature. Creep resistances of these alloys were found to be significantly superior to the existing aluminum alloys. The dominant strengthening mechanisms in these materials are grain size strengthening, Orowan strengthening and antiphase boundary energy strengthening. The strengthening mechanisms will also be discussed. Friction stir welding of Pandalloy demonstrated weld joint with 95% of parent metal strength.
Summary: Our presentation describes the development of a high strength, high temperature aluminum alloy based on the aluminum-scandium system. This alloy has been developed under a program funded by the Air Force Research Laboratory to provide a significant weight reduction benefit for hydrogen turbomachinery for rocket engines. Process development and scale up of these alloys are also being performed under an IR&D program at PWR.
