O. N. Senkov, UES, Inc., Dayton, OH; R. E. Perez, The Boeing Company, Canoga Park, CA

Summary:

A Sc-modified 7xxx alloy having exceptional specific properties is under development for cryogenic engine applications. In this presentation, cryogenic mechanical properties of forgings made of the developmental alloys will be reported and compared with the properties of forgings made of a 7050 alloy. A 76-mm diameter direct chill cast ingot, as starting material, was hot worked and then upset forged to produce forging pancakes with a diameter of 110 mm and height of 75 mm. The pancakes were heat treated to T6 and T7 tempers. Smooth and notched tensile round specimens were extracted from different sections of the heat-treated pancakes in three orthogonal directions, i.e. radial, transverse, and axial. These specimens were tested at liquid helium (T = 4 K), liquid nitrogen (T = 77 K) and room temperatures. Specimens for the high cycle fatigue had the transverse orientations and they were tested at T = 77 K in the life range of 10⁴ to 10⁷ cycles.