| Abstract Scope |
The integration of hydrogen fuel blends to advance higher-efficiency industrial gas turbines (IGT) for power generation presents material challenges, including higher-temperature thermal loads and environmental degradation. Ni-based superalloys processed by laser powder bed fusion (L-PBF) are being employed for certain IGT combustor components. This study, in support of larger elevated temperature materials evaluation at NETL, investigates the strain-controlled low cycle fatigue (LCF) behavior of L-PBF Alloy 625, Haynes 282 (H282), and Alloy 718 at 650°C, with a load R-ratio of 0.05 and strain ranges from 0.5% to 1.5%. L-PBF cylindrical blanks were stress-relieved and commercially heat treated, then machined into LCF test bars. Both the Alloy 625 and H282 showed an equiaxed microstructure after heat treatment, while Alloy 718 retained columnar grains due to grain boundary pinning by the δ-phase. The S-N curves revealed that the L-PBF superalloys exhibited comparable LCF performance to their wrought counterparts. Hysteresis loop analysis indicated cyclic hardening for Alloy 625 and cyclic softening for H282 and Alloy 718. Microstructural examination by SEM-EDS and EBSD confirmed minimal defects, except for Alloy 718, where secondary cracks emanated from larger entrapped gas pores (~10 μm), only at high strain ranges. Fracture surfaces displayed typical surface crack initiation, with lower strain ranges showing stage one initiation from surface grains and higher strain ranges having multiple initiation points. This research provides critical fatigue and microstructural data, accelerating the selection of suitable materials for fuel injectors in next-generation IGTs. |