Effect of microstructure on high-cycle fatigue strength of an oxide dispersion strengthened Ni-base superalloy, MA758, was studied at temperatures ranging from room temperature to 950℃. Three kinds of materials with different microstructures were produced by different thermo-mechanical treatments: with a fine and equiaxed grain structure, with a coarse and highly elongated one, and with an intermediate and elongated one. The microstructure was found to have a pronounced effect on the fatigue strength in this alloy, with did not obey a simple correlation with the tensile strength, as can be in usual metallic materials. The optimum microstructure also behaved in a complicated manner depending on test temperature. These features were studied on the basis of the resistance to the fatigue crack initiation, as well as that to the crack propagation. The positive role of oxidation film in the fatigue crack initiation, to which it was worthy to pay special attention, was also identified and discussed.
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