In Situ High-Cycle Fatigue Reveals Importance of Grain Boundary Structure in Nanocrystalline Cu-Zr
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Nanocrystalline metals typically have high fatigue strengths but low resistance to crack propagation. Amorphous intergranular films are disordered grain boundary complexions that have been shown to delay crack nucleation and slow crack propagation during monotonic loading by diffusing grain boundary strain concentrations, which suggests they may also be beneficial for fatigue properties. To probe this hypothesis, in situ transmission electron microscopy fatigue cycling is performed on Cu-1 at.% Zr thin films thermally treated to have either only ordered grain boundaries or amorphous intergranular films. The sample with only ordered grain boundaries experienced grain coarsening at crack initiation followed by unsteady crack propagation and extensive nanocracking, whereas the sample containing amorphous intergranular films had no grain coarsening at crack initiation followed by steady crack propagation and distributed plastic activity. Microstructural design for control of these behaviors through simple thermal treatments can allow for the improvement of nanocrystalline metal fatigue toughness.
JDS and TJR were supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Science and Engineering Division under Award DE-SC0014232, and the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program. BLB, KH, CMB, and NMH were supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Science and Engineering Division, under FWP 18-013170. The SCGSR program is administered by the Oak Ridge Institute for Science and Education for the DOE under Contract DE-SC0014664. TEM work was performed at the UC Irvine Materials Research Institute (IMRI). SEM and FIB work was performed at the UC Irvine Materials Research Institute (IMRI) using instrumentation funded in part by the National Science Foundation Center for Chemistry at the Space-Time Limit (CHE-0802913). Additional FIB and TEM work was performed at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. DOE’s National Nuclear Security Administration under Contract DE-NA-0003525. The views expressed in the article do not necessarily represent the views of the U.S. Department of Energy or of the U.S. government.
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