Experimental investigation and thermodynamic calculation on phase precipitation of inconel 740

A novel nickel-based superalloy INCONEL 740 was under development for application in ultra-supercritical superheater tubers above 750°C. The precipitation behaviors of η phase and γ′ particles of the alloy were investigated through experimental study and phase computation. Experimental results showed that η phase formed a Widmanstätten pattern structure following long-term exposure at elevated temperatures and that the coarsening of γ′ particle follows a cube rate law: r−3 ∝ t. Thermodynamic calculation results showed that Al and Ti had an important effect on the precipitation behavior of γ′ and η phases. Two suggested novel modified alloys, wherein the Al and Ti contents were modified, were designed and melted for the experimental study. The preliminary results indicated that the modified alloys exhibited higher structural stability following long-term exposure at 750°C till 5000h.