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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influenced by interaction between dislocation and secondary M 23 C 6 carbides than creep strength at higher temperatures. The decrease of interparticle spacing with increasing creep temperature due to dissolution and coarsening of secondary precipitates caused the decrease of the creep strength. The dissolution of secondary M 23 C 6 carbides led to the change of creep mechanism from creep predominantly govern by precipitate/dislocation interaction to the intragranular dislocation process involving climb of dislocations.

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c) d) Fig. 3. Microstructure of Ni-Cr-W based alloy after creep testing at 1373 K (a) M 23 C 6 carbide with corresponding diffraction pattern, (b) carbides M 23 C 6 and M 6 C with corresponding diffraction pattern, (c) chemical composition of M 23 C 6 and (d) chemical composition of M 6 C Fig. 5 shows the dependence of the ratio ̇/ ̇ of the creep rate in tertiary region normalized to an initial creep rate which was close to that at the beginning of tertiary creep region against strain. The results demonstrate that the rate of increase the ratio value is dependent on the fracture ductility. The steepness of the curves measured at 1373 K in Fig. 5 increases with decreasing value of applied stress. One can see that fast increase of ratio value with strain can be associated with low ductility during tertiary region.