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The high-temperature low-cycle fatigue (HTLCF) behavior of mechanically alloyed oxide dispersion strengthened MA 754 nickel-base alloy was studied under strain-controlled condition at 850°C. Specimens were cut from the longitudinal and the long transverse directions of the bar stock. Triangular strain cycles as well as strain cycles with hold times were employed in this study. In general, longitudinal specimens exhibited the longest lives, long transverse specimens the shortest lives. The cycles with tensile hold times were the most damaging to the HTLCF lives of specimens of both orientations. The difference between the HTLCF response of the alloy in the longitudinal and the long transverse orientations is interpreted in terms of factors such as modes of crack initiation and propagation, anisotropy in crack growth rates, and the directionality in creep properties. Three models for HTLCF lifetime were evaluated for their ability to correlate the fatigue data on MA 754 in both orientations. These models are the Strain Range Partitioning Model (SRP), the Frequency-Separation Model (FS), and the Frequency-Modified Damage Function (FMDF). The correlations of the data, having the smallest standard deviations of 0.22 and 0.14 for the longitudinal and the long transverse orientations, respectively, were by the FS model. The FMDF and the SRP models had standard deviations, for the longitudinal orientations, of 0.25 and 0.33, respectively.
MA 754, high-temperature low-cycle fatigue, texture, nickel-base oxide dispersion strengthened alloy, life prediction
Scientist, Brown Boveri Research Center, Baden/Dättwil,