Abstract
This work investigates the microscopic deformation mechanisms of an extruded, precipitation-strengthened AZ80 magnesium (Mg) alloy subjected to strain-controlled low-cycle fatigue using in situ neutron diffraction measurements. Results demonstrate that the plastic deformation during cyclic loading is dominated by the alternating {10.2} extension twinning and detwinning mechanisms. The observed deformation mode is strongly texture and precipitate dependent. For the initial texture, the tested material has two major texture components which result in the occurrence of extension twinning during both compression and reverse tension in the first two cycles. The prolonged detwinning process in the following cycles is proposed to relieve the shear stress field of {00.2} grains, leading to the disappearance of twinning. The precipitation strengthening results in an increase of the critical resolved shear stress (CRSS) by ~33 MPa for the extension twinning in this AZ80 alloy. The synergistic effects of the initial texture, precipitation strengthening, and load sharing of various grain families and phases contribute to the complicated evolution of dominant deformation mechanisms, among which elevated dislocation activities are believed to be responsible for the relatively poor low-cycle-fatigue lifetime when compared to other Mg alloys.
Original language | English |
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Article number | 140860 |
Journal | Materials Science and Engineering: A |
Volume | 806 |
DOIs | |
State | Published - Mar 4 2021 |
Funding
This work is supported by the US National Science Foundation ( DMR 1809640 to the University of Tennessee & DMR 1809696 to the University of Illinois ). DX also acknowledges a graduate fellowship from Center for Materials Processing at the University of Tennessee. Neutron diffraction work was carried out at the Spallation Neutron Source (SNS), which is the U.S. Department of Energy (DOE) user facility at the Oak Ridge National Laboratory , sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences . The authors thank Dr. M. J. Frost at SNS for the technique support. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. This work is supported by the US National Science Foundation (DMR 1809640 to the University of Tennessee & DMR 1809696 to the University of Illinois). DX also acknowledges a graduate fellowship from Center for Materials Processing at the University of Tennessee. Neutron diffraction work was carried out at the Spallation Neutron Source (SNS), which is the U.S. Department of Energy (DOE) user facility at the Oak Ridge National Laboratory, sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences. The authors thank Dr. M. J. Frost at SNS for the technique support. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.
Keywords
- Deformation mode transitions
- In situ neutron diffraction
- Low cycle fatigue
- Magnesium alloy