Creep-induced Nonlinear Ultrasonic Change in Nickel-based Super alloy, Inconel 718.

Abstract

We investigated the evolutions of nonlinear acoustic characterization: three-wave mixing, with electromagnetic acoustic resonance (EMAR) throughout the creep life in Nickel-based superalloy, Inconel 718, which has high temperature strength effected by γ″(Ni₃Nb) phase at approximately 973 K and is determined that the γ″phase disappearance lead to the creep rupture. EMAR was a combination of the resonant acoustic technique with a non-contact electromagnetic acoustic transducer (EMAT).

We used bulk- shear-wave EMAT, which transmits and receives shear wave propagating in thickness direction of a plate specimen. Creep tests were carried out at 973 K, and 310 MPa and interrupted at several time steps. The nonlinear acoustic parameter showed they increased from 60% of creep life to rupture. We interpreted these phenomena in terms of dislocation recovery, recrystallization, and the coarsening and disappearance of γ″phase and the initiation and growth of creep void, with support from the SEM and TEM observation.