Deformation Mechanisms Governing Torsional Fatigue Failure of Additively Manufactured Metals at High Temperatures

Recent advances in the 3D metal printing/additive manufacturing technology have allowed for the realization and rapid production of nickel-based metal superalloy components, extending their geometric design space and mechanical performance envelope. Nevertheless, there is a need to ensure that these additively manufactured components can withstand in-service operational conditions while meeting necessary functional requirements and durability.

Torsional fatigue, characterized by cyclic twisting loads, is often an underlying cause for failure of nickel-based metal superalloys used in the extreme environments of rocket and jet engines, high performance automobiles, and pressure vessels. These extreme temperature environments are characterized by a complex loading state, in which the deformation mechanisms contributing to torsional fatigue failure remain unclear.

This award supports fundamental research to delineate the principal deformation mechanisms at the microstructural level, which govern torsional fatigue failure of additively manufactured nickel-based metal superalloys subject to varying service conditions. This research will advance the current state of knowledge and maximize durability and viability of these alloys for in-service use, thereby maturing the current technology.

Additionally, this study will broaden participation, outreach, and professional training of under-represented minority undergraduate and graduate students in STEM research spanning across the disciplines of mechanics, manufacturing, and materials science and engineering. Research outcomes will be used to establish enhanced educational curriculum/tools, including incorporation of a research project-based teaching and learning structure.

The fundamental problem that this research addresses is capturing the micron scale to structural scale deformation response spectrum experienced by additively manufactured nickel superalloys under torsional fatigue loading conditions at ambient and high temperatures representing in-service component conditions. The role of temperature, varying cyclic torsional loadings, and additive manufacturing processing conditions and build orientation will be explored.

A variety of material characterization techniques, such as energy dispersive spectroscopy, X-ray diffraction, and electron microscopy, will be used in conjunction with extensive fatigue testing to capture the driving microstructural mechanisms leading to torsional fatigue crack initiation and growth. It is anticipated that outcomes resulting from this study will reveal how torsional response of these alloys is impacted in terms of microstructural evolution under ambient and in-service operational conditions, potentially providing insights that will contribute to an understanding of their multiaxial fatigue response.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.