PSI - Issue 23

Petr Král et al. / Procedia Structural Integrity 23 (2019) 287–292 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 6 shows dependence of creep damage tolerance factor λ, Ashby and Dyson (1984) , Dyson and Gibbons (1987). This parameter is often used for assessment of material susceptibility to localized cracking at strain concentrations. The λ factor is defined as: = ̇ (1)

w here ε R is strain to fracture, ̇ is minimum creep rate and t R is time to fracture. The value of λ is higher than 1 and it can reach the value of 20, Ashby and Dyson (1984). The values of λ higher than 2.5 indicate that the fracture is influenced by necking-dominated creep damage, Dyson and Gibbons (1987) and Sklenicka et al. (2017). The values lower than 2-2.5 suggest that creep damage is influenced by cavitation. The results demonstrate that the value of λ are in the range of 1.3 – 2.1. The low values of λ suggest that fracture is influenced by cavitation damage independently on the applied stress and testing temperatures. The analyses of fracture surfaces of Ni-Cr W based alloy tested at 1173 and 1373 K (Fig. 7) is consistent with the assessment of creep damage using λ factor. The results demonstrate that the creep damage occurred by interdendritic fracture mode.

Fig. 4. Stress dependences of Ni-Cr-W based alloy measured at 1173, 1273 and 1373 K

Fig. 5. Dependence of the ratio ̇/ ̇ on strain

Fig. 6. Dependence of λ factor on time to fracture