Low Cycle Fatigue Characterization of Additive Manufactured Specimen With as Printed Surface Roughness Made From Multiple Nickel Based Super Alloys

Additive manufacturing is a transformative technology that can enable advanced designs for gas turbines that are not otherwise possible. While the expansion of design envelope can greatly contribute to improvement in efficiency and fuel flexibility of gas turbines, limitations in material properties can adversely affect durability of additively manufactured components if not properly characterized and accounted for in the design phase. An important consideration for durability of turbine components is the LCF (Low Cycle Fatigue) life, and it is influenced by the surface effects that are characteristic of the layer by layer build process of additive manufacturing. The influence of as printed surface texture on LCF properties of multiple additive manufactured alloys is evaluated in this work as part of a broader incorporation of additive alloys in gas turbines. Hastelloy-X is a commonly produced alloy that is utilized in combustion components, enabling state of the art fuel flexibility and hydrogen combustion. An Inconel-939 derivative alloy has been recently utilized in static turbine components due to its high temperature creep capability and oxidation resistance, resulting in improved cooling efficiency and increased turbine performance. In this paper, specimens with as printed and machined gauge (machined from additive manufactured bars) are produced with both Hastelloy-X and IN939 derivative alloys. Specimens are tested for LCF at multiple temperature and strain range conditions and comparisons between as printed (or rough gauge) versus machined gauge specimen are made to determine influence of as printed surface conditions. Results of the experiments for both alloys are presented in normalized form to evaluate performance of as printed versus machined surfaces at various test conditions. Fractographic analysis is conducted on IN939 derivative failed specimens and the influence of surface roughness on crack initiation at the microstructural level is discussed.