PSI - Issue 68

Birhan Sefer et al. / Procedia Structural Integrity 68 (2025) 1129–1139 Author name / Structural Integrity Procedia 00 (2025) 000–000

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Figure 5. Representative fracture surfaces taken from SSRT specimens tested in argon (left) and hydrogen (right) at a) room and b) high temperature for NCF3015 material. Higher magnification micrographs taken in the area marked with numbers in the white boxes are given below the overview micrographs. Finally, Figure 5 shows SEM-micrographs taken from the fracture surfaces of the NCF3015 material after SSRT testing in Ar (left) and H 2 (right) at room (Figure 5a) and high temperature (Figure 5b). In general, for the specimens tested at room temperature in both gases, a ductile type of fracture surface was observed. No flat regions were observed on the fracture surfaces in either case. The fracture surfaces were full of dimples generated by microvoid coalescence. However, for the Ar specimen the completely ductile appearance was also featured with some cleaved secondary phase particles dispersed throughout the fracture surface. Moreover, although the H 2 specimen exhibited almost entirely ductile dimple like fracture surface in small areas close to the surface of the hole mixed fracture mode (brittle and ductile) was also identified. These areas were relatively small compared to the entire fracture surface, and thus not influenced notably the properties as seen from Table 3. In contrary to the room temperature tested specimens, both specimens tested in Ar and H 2 at high temperature showed little to no macroscopic deformation. The fracture surfaces of both specimenshad large areas with intergranular fracture as primary fracture appearance (see Figure 5b). For both gases, there were also small areas where mixed, ductile and brittle, type of fracture was observed. It should be mentioned that the intergranular type of fracture was not possible to associate to hydrogen. Therefore, it may be corroborated that intergranular type of fracture mode is general behaviour of the NCF3015 material at high temperature regardless of the environment.