PSI - Issue 71

Pramod Ravindra Kushwaha et al. / Procedia Structural Integrity 71 (2025) 74–81

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Table 2. Results of small punch creep test on Su-263 samples

Time of hump appearance (hr.)

Percentage time elapsed

Minimum creep rate (mm/hr.) (1.54 ± 0.30) x 10 -4 (2.32 ± 0.35) x 10 -4 (2.50 ± 0.40) x 10 -4

Load (N)

Time of Rupture (hrs.)

48.00

54.4 %

650

88.20 ± 1.50

21.00 14.00

42.0 % 39.8 %

700 750

50.10 ± 1.50 36.15 ± 1.50

4.3 SEM fractography of Su-263 The fractography analysis of small punch creep-tested samples revealed distinct differences in fracture patterns. The fractography showed plastic intergranular mode at lower loads, shown in Fig. 5, and highly brittle intergranular fracture at higher loads, shown in Fig. 6. In Fig. 5(c), the enlarged section of the fractured sample showed elongated grains, indicated by arrows, with the fracture plane inclined relative to the applied stress. In contrast, Fig. 6(c) displayed equiaxed grain morphology, where the fracture surface exhibited a zig-zag pattern. Yokobori and Ichikawa (Yokobori and Ichikawa 1965) observed similar behaviour in brittle materials, noting zig-zag crack propagation perpendicular to high applied stress fields (Yokobori and Toshimitsu 1999). Additionally, creep crack growth along grain boundaries in a zig-zag manner resulted from the subcritical linkage and coalescence of grain boundary creep cracks and the similar behaviour was seen at 750 N.

(a)

(b)

(c)

Fig. 5. SPC ruptured nascent samples of Su-263 at 650 °C and 650 N

(a)

(c)

(b)

Fig. 6. SPC ruptured nascent samples of Su-263 at 650 °C and 700 N In fractography, it can be seen that the material failed and the surface was still close to the indenter ball from all the directions as the material had not left the indenter ball surface, but the fractography showed the material closeness was high at 650 N, indicating plastic or ductile failure of the fractured surface. Also, it was observed that there were fine precipitates in case of 650 N test, shown in Fig. 5c, and at 700 N test, the deformation induced dissolution of precipitate has been observed in Ni-based superalloy which was also studied by Dao-Guang He, Y.C. Lin (He et al. 2018). The precipitates dissolution was preceeded and seen at temperature 650 °C which was generally seen after 750 °C (Zhao et al. 2001) because of the applied load in the sample.