High temperature properties and fatigue strength of novel wrought γ/γ′ Co-base superalloys

This paper presents the high temperature yield and fatigue strength as well as thermophysical properties of two polycrystalline wrought γ/γ′ Co-base superalloys developed for application in a temperature regime above 700 °C. The alloys CoWAlloy1 (Co42Ni32Cr12Al6W3Ti2.5Ta1.5 + Si,C,B,Zr,Hf) and CoWAlloy2 (Co41Ni32Cr12Al9W5 + Ti,Ta,Si,C,B,Zr,Hf) exhibited solidus temperatures of 1070 °C and 1030 °C, respectively, and a γ′ fraction of about 50%. CoWAlloy2 displayed a rather high Young’s modulus of 250 GPa. The two Co-base superalloys showed a good high temperature strength exceeding Ni-base disc alloys U720Li and Waspaloy at temperatures above 800 °C. When comparing the yield strength from tensile and compression tests, no asymmetry could be found. The low-cycle fatigue life of CoWAlloy2 at a total strain amplitude of 0.5% is similar to that of U720Li and Waspaloy (about 370 cycles,R= −1). During long-term aging for 1024 h at 750 °C, no additional phases were formed and the room temperature hardness barely changed.