Effect of microstructure on high cycle fatigue strength of an oxide dispersion strengthened Ni base superalloy at high temperature
Okazaki Masakazu; Yamazaki Yasuhiro; Okabe Michio
Abstract:The effect of microstructure on the high cycle fatigue strength of an oxide dispersion strengthened Ni base superalloy, MA758, was studied at temperatures ranging from room temperature to 950 degree. 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, which did not obey a simple correlation with the tensile strength, as can be seen 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 fatigue crack initiation, as well as that to 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. Key Words:ODS alloy, microstructure, thermo-mechanical treatments, high pressure fatigue, crack initiation, oxidation film