PSI - Issue 80

Tomáš Vražina et al. / Procedia Structural Integrity 80 (2026) 244 – 255 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 4 Comparison of cyclic deformation behavior in Sanicro 25 and FeAlOY. (a-b) Cyclic hardening/softening curves of Sanicro 25 and Fe alloy.(c-d) Plastic strain amplitude vs. number of cycles for Sanicro 25 and FeAlOY.

3.3. Fractography Fig. 5 and 6 show fracture surfaces of FeAlOY and Sanicro 25 respectively, where the intergranular cracking occurred in close proximity to the crack initiation site. However, their subsequent fracture development differed. Intergranular cracking in FeAlOY dominated during stage II, followed by a final brittle fracture zone (stage III). The most pronounced stage II intergranular cracking was observed a total strain amplitude of 0.35% in Fig. 5(e). Increasing Fig. 5(c) or decreasing Fig. 5(d) strain amplitude resulted in a decrease in the proportion of intercrystalline fatigue crack on fracture surface. Although not shown the entire fracture surface after straining at 0.45% it exhibited transgranular brittle cracking. Contrary to these findings, the intergranular cracking in Sanicro 25 transitioned into transgranular ductile fracture characterized by fatigue striations. These striations continued until the end of stage II. Stage III was marked by the appearance of dimples, indicative of ductile overload failure. The grain facets revealed near the initiation region were not entirely smooth as shown in Fig. 6(d-f) but exhibited signs of plastic deformation in the form of PSMs aligned with one (Fig.6 (d-e)) or more slip systems (Fig. 6(f)). Depending on the strain amplitude and fracture progression, PSMs varied in appearance starting from the distanced fine PSMs (Fig.6(f)) to more densely packed PSMs (Fig. 6(e)) until the dense thick features were formed (Fig. 6(d)).