High temperature creep properties of a linear friction welded newly developed wrought Ni-based superalloy
Résumé
AD730™ Ni-based superalloy specimens in solution-treated conditions were linear friction welded. Then, post-weld heat treatment (PWHT), consisting of γ′ sub-solvus solution treatments followed by aging, was conducted on the linear friction welded samples. High temperature creep tests were performed on the as-welded and PWHTed joints at two different temperatures: 700 °C under 600 and 750 MPa stress levels, and 850 °C under 100 and 200 MPa stresses. The creep resistance of the PWHTed joints was higher than that of the as-welded samples. The PWHTed joints exhibited better ductility than that of the base material at 850 °C, while they showed slightly lower creep life at 700 °C in comparison to the base metal. Microstructure examination showed that cracks initiated at the interface of oxidized particles at 700 °C. The decrease in creep resistance of the AD730™ Ni-based superalloy at 850 °C was related to a combination of the formation of precipitate-free zones (PFZ) in the vicinity of the grain boundaries (GBs) and microcracking assisted by oxidation. The Larson-Miller Parameter (LMP) was used to correlate the creep strength, temperature and time to failure for the as-welded and PWHTed samples. LMP values varied between 21.5 × 103 and 24.5 × 103. It was found that in the investigated temperature range, the PWHTed AD730™ has similar creep characteristics as Udimet™720 Li and Inconel 738LC at low values of LMP and better creep properties than those of the Inconel 617 alloy at higher LMP values.