PSI - Issue 71

Prasanna Dupare et al. / Procedia Structural Integrity 71 (2025) 118–125

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Fig. 6 Fractography a)Fracture surface of LCF specimen b)Transgranular mode of fracture c)Fracture surface of 1min hold specimen d) Fracture surface of 10 minutes hold specimen) e)Transgranular striations f) Intergranular grain facet g) striation for 10 minutes hold test

Fig. 6(c) and 6(e) shows fracture surface of 1 minute hold tested specimen. It shows multiple crack initiation sites. This indicates that creep damage associated with hold time assists in multiple crack nucleation. Fig. 6(e) shows fatigue striations as well as crack along grain boundaries. This indicates this alloy undergoes mixed mode i.e. partly transgranular and partly intergranular cracks for 1minute hold CFI test. Transgranular cracks causes matrix damage whereas intergranular cracks are because of grain boundary damage. Fig. 6(d), 6(f), and 6(g) show fracture surface of 10 minutes hold CFI tested specimen. Multiple crack initiation sites were observed. Fig. 6(f) shows grain facets indicating intergranular damage in the material. Fig. 6(g) shows transgranular striations. This indicates material undergoes mix mode of deformation for 10 minutes hold CFI test. During the hold time, creep cavitation initiated at grain boundaries or particles, and these cavities gradually grew and coalesced, forming larger voids over the course of subsequent hold times. This allows fracture to follow an intergranular path. This process ultimately led to the formation of intergranular cracks.