High-Temperature Cobalt-Tungsten Alloys for Aerospace Applications 640501
The high-temperature capability and workability of cobalt-tungsten alloys for aerospace applications is discussed. The average life at 1850 F and 15,000 psi of the strongest previously reported alloy Co-25W-1Ti-1Zr-0.4C was doubled from 92 to 185 hr by small additions of chromium and rhenium. At 2200 F and 5000 psi the strongest alloy, Co-25W-1Ti-1Zr-3Cr-2Re-0.4C, had a rupture life of 23 hr; the elevated temperature rupture strength compared favorably with the strongest available conventional (high chromium) cobalt-base alloys.
It is particularly significant that even the strongest alloys of this series were readily hot-rolled. Elongations as high as 31% were obtained at room temperature with annealed cold-rolled sheet specimens. The good ductility obtained suggests that these alloys could be fabricated into complex shapes required for various aerospace and other applications.
Elevated temperature tensile strengths of annealed sheet of the strongest chromium- and rhenium-modified alloys were approximately the same as for the cast alloys. The elongation of the wrought material was substantially greater.
Although the strongest alloys had a chromium content of only 3%, they did not oxidize catastrophically in air. When they were coated with a commercial aluminum-iron coating, oxidation in 300 hr at 1900 F was negligible.