Creep behavior and microstructural characterization of iron-nickel and nickel-based superalloys

New superalloys are constantly being developed to fulfill the increased demand for alloys with high creep resistance and low manufacturing costs. This study subjected two alloys to comparative creep tests and microstructural characterization. A novel low-cost iron-nickel superalloy with intermediate Ni and Fe content was designated in this work as Fe-Ni-Cr and the NIMONIC 80A with a high Ni. Creep experiments were carried out at temperatures ranging from 650 to 750 ◦ C and loads ranging from 500 to 600 MPa. Microstructural characterization and surface analysis were carried out using microscopy techniques such as optical, SEM with EDS, and TEM. For phase quantitative identification, Rietveld refinement was utilized. Compared to NIMONIC 80A, the new Fe-Ni-Cr superalloy showed higher creep resistance. The Fe-Ni-Cr alloy has higher percentages of carbon and iron and the addition of niobium, resulting in the formation of γ (cid:3) intermetallics and carbides rich in iron and niobium. These carbides and intermetallics operate as obstacles to dislocation glide and climb, lowering the creep rate. Compared to Fe-Ni-Cr, the reduced carbides in NIMONIC 80A promote relative slip between grains during deformation, facilitating creep rate acceleration and early failure.