PSI - Issue 23

Jaroslav Polák et al. / Procedia Structural Integrity 23 (2019) 275–280 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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(a)

(b)

Fig. 5: The cavity coalescence in specimen cycled with  a = 4 × 10

-3 and dwells in tension; (a) the cavities distributed along the grain boundary;

(b) linkage of the cavities leading to early grain boundary crack formation.

3.2. Thermomechanical fatigue Fatigue hardening/softening curves in cycling with four strain amplitudes of mechanical strain between 250 °C and 700 °C (in -phase) are shown in Fig. 6. Rapid cyclic hardening is interrupted by the initiation and growth of the principal crack before stress amplitude is saturated.

Fig. 6. Cyclic hardening/softening curves in thermomechanical in-phase cycling for four strain amplitudes; stress amplitude vs. number of cycles. The damage mechanisms in thermomechanical cycling were found similar to that in constant strain rate cycling (see Fig. 7). The oxide extrusion along the boundary is cracked and the principal crack follows grain boundaries