PSI - Issue 80

Marie Kvapilová et al. / Procedia Structural Integrity 80 (2026) 269–278 Author name / Structural Integrity Procedia 00 (2019) 000–000

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50 µ m

50 µ m

a)

b)

Fig.8. Microcracks in crept material (a) 800°C, 200MPa, (b) 800°C, 500MPa.

10 µ m

10 µ m

a)

b)

Fig.9. MC and g ´precipitates in specimen creep at (a) 700°C, 400 MPa (b) 900°C, 60MPa.

3.3. Investigation of fracture surfaces Fractographic analysis revealed a clear dependence of fracture surface morphology on the applied stress and temperature conditions. In all cases, the fracture was of the intergranular type, but at 700°C and 800°C, across all applied stresses, the fracture surfaces showed features typical of additively manufactured materials- fracture followed grain boundaries aligned with the printing direction. However, at the lowest applied stress of 200 MPa at 800°C, and particularly at 900°C, the fracture morphology changed significantly. These conditions promoted growth and reorientation of grain, and coarsening of carbides, leading to fracture along the boundaries of thermally modified grains (Fig.10). Consequently, the presence of continuous and thick carbides at grain boundaries facilitates the initiation and propagation of microcracks along grain boundaries, leading to intergranular fractures. In Fig. 10b, slight necking of the specimen can also be observed. This shift in fracture behaviour was accompanied by increased ductility of the specimens, which is likely related to the degradation of strengthening phases such as g ´ precipitates and MC carbides.