Enhanced mechanical properties of wrought γ′-strengthened Co-base superalloys by adjusting the relative content of Al and Ti

Abstract

With the goals of exploring the feasibility of improving the yield strength without decreasing the hot workability, four novel Co–30Ni-(7-x)Al–2W-1.5Mo–1Ta-(3.5 + y)Ti–12Cr-0.1Hf-0.08C-0.08B-0.4Si-0.01Zr (x = 0, 1, 1.5, 3, y = 0, 0, 0.7, 1.4 at%) γ′-strengthened wrought Co-base superalloys were designed, and the effects of Al and Ti on microstructure and properties of γ′-strengthened wrought Co-base superalloys were analyzed. Comparing the alloys 7Al-3.5Ti, 5.5Al-4.2Ti and 4Al-4.9Ti with the similar hot workability, the Al(at%)/Ti(at%) in the γ′ decreased with the decrease of Al(at%)/Ti(at%) in the alloys, this composition change in the γ′ made the alloys’ yield strength at room temperature and 800 °C increase from 915 MPa to 1025 MPa and from 764 MPa to 826 MPa, respectively. Based on the 6Al-3.5Ti alloy, the addition of 1 at% Al changed the γ′ compositions, which resulted in a decrease of yield strength at room temperature by 45 MPa but a significant increase of yield strength by 108 MPa at 800 °C, and this significant increase of yield strength at 800 °C may also be associated with the formation of numerous microtwins in 7Al-3.5Ti alloy; In the four experimental alloys, Mo preferentially partitions to the γ matrix, the relative content of Al and Ti has a negligible influence on the hot deformation resistance at 1150 °C, and there is no harmful phase after a heat treatment of 900 °C at 8 h + 750 °C at 12 h.