AN ADVANCED CAST-AND-WROUGHT SUPERALLOY (TMW-4M3) FOR TURBINE DISK APPLICATIONS BEYOND 700°C

A new cast & wrought (C&W) superalloy, designated as TMW-4M3, has been developed on the basis of our innovative concept for applications of turbine disks and other components beyond 700 degrees C. TMW-4M3 contains 25 wt% Co and 6.2 wt% Ti, which are higher than that of commercial disk alloys. Full-scale pancakes with 400 mm in diameter and 50 mm in thickness were manufactured from TMW-4M3 alloy via a process route of triple-melting, billet making and disk forging. The investigations on the microstructure and the mechanical properties including tensile strength, creep resistance, fatigue strength and resistance to crack propagation of TMW-4M3 indicate that the alloy provides a 100MPa advantage in 0.2% yield strength at 750 degrees C and a 76 degrees C temperature advantage in 0.2%-strain creep performance loaded under 630MPa over Alloy 720Li (U720Li). The alloy maintains its gamma/gamma' two-phase structure exposed at 750 degrees C for up to 5000 hours. The increment of strength at high temperatures is attributed to the precipitation hardening caused by higher volume fraction of the secondary gamma' precipitates and twin boundary strengthening as a result of high density of annealing twins.