PSI - Issue 23

Roman Petráš et al. / Procedia Structural Integrity 23 (2019) 209–214 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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The respective profile of the FIB cut documented in Fig. 4b shows the crack formation. Instead of the continual crack development from the specimen surface; the voids developed at the grain boundaries can be recognized. The detail providing the higher magnification reveals the cavity formation due to vacancy concentration at the location of the grain boundaries indicating the early crack nucleation.

3.4 Longitudinal cross-section inspection

Additionally to the surface crack formation the internal damage was investigated on the longitudinal cross-sections produced in the direction of the loading axis. The damage in the interior of the material was scrutinized on the polished surfaces by means of SEM. Fig. 5 documents the longitudinal cut of the specimen strained under LCF conditions in the air. The crack which developed in the specimen surface propagates intergranularly. The cross-section was also studied under high magnification revealing that interior of the material is free of cavities and intergranular cracks. The cross-section of the specimen subjected to the LCF conditions in high vacuum is depicted in the Fig. 6 .

Fig. 5. Longitudinal cross-section of the specimen gauge length strained under LCF loading conditions in the air with total strain amplitude 7x10 3 revealing the fatigue crack development.

(a)

(b)

Fig. 6. Longitudinal cross-section of the specimen gauge length strained under LCF loading conditions in the vacuum with total strain amplitude 7x10 -3 revealing (a) the surface crack; (b) the internal damage.