Oxidation assisted recrystallization and cracking at grain boundaries in Nimonic 80 A during elevated temperature service

Oxidation and cracking at the grain boundary (GB) of wrought Nimonic 80 A alloy exposed to 550 °C for 2000 h and statically loaded to 490 MPa, is studied. The GB cracks and transforms to a hierarchical structure with a nanoscale recrystallized Ni layer in the center flanked by ambilateral NiCr2O4/NiCrO3 layers. Widths of both layers increases with increasing proximity to the crack and the recrystallized crack bearing Ni layer oxidizes. Formation of the recrystallized Ni layer is attributed to oxidation of Cr and externally applied stress. Oxidation mechanism and cracking of the GB in Nimonic 80 A is discussed in detail.