Abstract
Crack propagation behavior was examined in creep-fatigue at high temperatures using center cracked plate (CCP) specimens of an oxide (Y2O3) dispersion strengthened (ODS) superalloy, Inconel MA754, manufactured by mechanical alloying and a Ni-base superalloy without oxide dispersion, Nimonic 75. The Inconel MA754 has coarse elongated grains whereas the Nimonic 75 has fine homogeneous ones. The results obtained are summarized as follows.(1) The transverse crack propagation of the Inconel MA754 at 1273K and 1173K was strongly affected by the microstructure. The crack arrested temporarily at the grain-boundaries perpendicular to the propagation direction while it propagated fast at the midway.(2) The average crack length through the thickness of specimen, which included about 15 grains, was measured by means of the DC potential drop technique during the test of Inconel MA754. The length increased smoothly without the crack arrest and the propagation rate was correlated well with the creep J-integral range.(3) Little difference was observed in the dl/dN-ΔJc relations between the Inconel MA754 and the Nimonic 75 (at 1173K and 1073K).(4) The crack propagation of the Inconel MA754 was much slower than that of the Nimonic 75. This high resistance of ODS superalloy against creep-fatigue crack propagation was caused by the excellent creep deformation property due to the oxide dispersion.
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