Abstract
Long term stress-rupture life at 600°C/450MPa of Nimonic 80A with various duplex grain size distributions has been investigated. Stress-rupture life of duplex grain size samples significantly increases from about 4512h in the bimodal condition to 6863h in the banding condition and to 10,765h in the wide-range condition. Plate-like Cr23C6 prefers to precipitate at transition region of small dynamic recrystallization (DRX) grains and large original grains in the bimodal condition, which can easily lead to grain boundary (GB) cracking. Cracking is also found at small equiaxed recrystallized GB where is enriched with strip-like Cr23C6 in sample with abnormal grains in the banding condition. Blocky Cr23C6 exhibits an orientation relationship with γ at GB in sample in the wide-range condition. Blocky TiC with average size about 7.5μm precipitates at GBs firstly and then also in the grain interior, while the fine TiC with size about 300nm is found in grain interior and the morphology changes from lageniform or oval shape to spherical one with prolonged stress-rupture life. The γ′ which maintains a coherent orientation relationship with γ is very stable. The duplex grain size distribution in the wide-range condition significantly improves stress-rupture life.
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