In-situ observation of crack coalescence during stress assisted grain boundary oxidation in Ni base superalloy 718 (InnovaXN13)

718 alloy is the most used Ni base superalloy in industry due to its high manufacturability and high resistance in extreme conditions. However, when subjected to very high stress, it is reported that this alloy can suffer from embrittlement by a Stress Assisted Grain Boundary Oxidation (SAGBO) mechanism at high temperature. In this proposal we will focus on the kinetics of the rate limiting crack coalescence stage of this damage mechanism and study its sensitivity to microstructural parameters such grain size, texture and precipitation state of the material. For this end, we will perform time-lapse observations of crack coalescence under load at 650 C, using phase contrast tomography. The initial and final 3D grain structure of the samples will be characterized by DCT. Digital volume correlation will be used to quantify the deformation of the material and results will be compared to crystal plasticity and phase-field simulations on the digital twin of the sample volume.