PSI - Issue 43

A. Shanyavskiy et al. / Procedia Structural Integrity 43 (2023) 215–220 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

218

4

Fig. 1. (a) Fatigue and (b) creep-fatigue crack growth rate as a function of elastic SIF at various test temperature.

Fig. 2a represents a comparison of the behavior of crack growth rate diagrams in terms of the elastic K 1 at the same high temperature 650°C for considered thermo -mechanical loading conditions of the C(T) specimens. As a result of the polycrystalline XH73M nickel-based alloy tests performed, it was found that from the crack growth rate point of view, the following order of arrangement of fatigue fracture diagrams is formed: isothermal creep-fatigue interaction, isothermal pure fast (f = 10 Hz) and slow (f = 1 Hz) fatigue. Fig. 2b shows a comparison of the fatigue fracture diagrams as a function the elastic SIF K 1 at the highest test temperature 750°C for harmonic (with a frequency 10 Hz) and trapezoidal cycle with the holding time during 120 sec at a maximum load.

Fig. 2. Comparison of crack growth rate under different type of loading at (a) 650 ° C and (b) 750 ° C.

It was observed that creep-fatigue interaction testing produce higher crack growth rate compared with pure fatigue conditions due to dwell time at elevated temperature. Comparison of results obtained under isothermal pure fatigue conditions have shown that at T = 23° C and T = 150 ° C temperature, the mechanism of transgranular fracture with fatigue striations (Fig. 3) is governing. With an increase in test temperature, the dominant fracture mechanism changes gradually. At T = 650 ° C, the features of intergranular fracture mechanism appear (Fig. 4a) that influences the acceleration of crack growth. An increase in temperature of test up to750 ° C leads to the domination of intergranular fracture mechanism (Fig. 4b).