SMALL VOLUME FATIGUE TESTING OF ADDITIVELY MANUFACTURED HYBRID IN718/XH67 AND IN939 Ni BASED SUPERALLOYS

Additively manufactured alloys are known to possess sufficient tensile strength-ductility combinations, matching their conventionally processed counterparts, and yet fail to perform under cyclic loading conditions. The complex, heterogeneous microstructure, resulting anisotropy and porosity distribution, as well as the surface roughness in additively manufactured alloys result in reduced fatigue life. Evaluation of fatigue behavior of these materials, especially during the alloy development stage, necessitates small-volume fatigue testing, to mimic the component geometry. It is also very pertinent during repair and component lifing, in Hybrid alloys, owing to the small sampling volume. This study explores a novel technique of small-scale fatigue specimens, for evaluating the fatigue behavior of a new Hybrid XH67- IN718 manufactured by the powder bed fusionlaser beam technique, in the as-printed condition, at room temperature. Comparisons are made with a high gamma prime (gamma) IN939 Ni based superalloy used in gas turbine hot section components. Miniature fatigue test specimens were designed to determine the fatigue life with the loading at 0.95 % yield strength, for both the Hybrid and the monolithic alloy, in the as-printed condition. Results will be discussed in the context of the observed failure mechanism, tensile properties, and the hierarchical microstructure.