Abstract
The microstructure and phase composition of an AlCoCrFeNi high-entropy alloy (HEA) were studied in as-cast (AlCoCrFeNi-AC, AC represents as-cast) and homogenized (AlCoCrFeNi-HP, HP signifies hot isostatic pressed and homogenized) conditions. The AlCoCrFeNi-AC ally has a dendritric structure in the consisting primarily of a nano-lamellar mixture of A2 (disordered body-centered-cubic (BCC)) and B2 (ordered BCC) phases, formed by an eutectic reaction. The homogenization heat treatment, consisting of hot isostatic pressed for 1 h at 1100 °C, 207. MPa and annealing at 1150 °C for 50 h, resulted in an increase in the volume fraction of the A1 phase and formation of a Sigma (σ) phase. Tensile properties in as-cast and homogenized conditions are reported at 700 °C. The ultimate tensile strength was virtually unaffected by heat treatment, and was 396±4. MPa at 700 °C. However, homogenization produced a noticeable increase in ductility. The AlCoCrFeNi-AC alloy showed a tensile elongation of only 1.0%, while after the heat-treatment, the elongation of AlCoCrFeNi-HP was 11.7%. Thermodynamic modeling of non-equilibrium and equilibrium phase diagrams for the AlCoCrFeNi HEA gave good agreement with the experimental observations of the phase contents in the AlCoCrFeNi-AC and AlCoCrFeNi-HP. The reasons for the improvement of ductility after the heat treatment and the crack initiation subjected to tensile loading were discussed.
| Original language | English |
|---|---|
| Pages (from-to) | 229-240 |
| Number of pages | 12 |
| Journal | Materials Science and Engineering: A |
| Volume | 647 |
| DOIs | |
| State | Published - Oct 28 2015 |
Funding
The authors very much appreciate the original proposed idea of this work from D.B. Miracle of the Air Force Research Laboratory (AFRL) and his many great comments and discussions on this paper. ZT, LJS, GW, and PKL would like to acknowledge the financial support from the Department of Energy (DOE) Office of Nuclear Energy’s Nuclear Energy University Program (NEUP) 00119262 , and the DOE, Office of Fossil Energy, National Energy Technology Laboratory ( DE-FE-0008855, DE-FE-0011194, and DE-FE-0024054 ), with R.O. Jensen, Jr., L. Tian, V. Cedro, S. Lesica, S. Markovich, J. Mullen, and R. Dunst as program managers. PKL thanks the U.S. Army Research Office project (W911NF-13-1-3080438) with the program manager, S.N. Mathaudhu and D.M. Stepp. The authors also gratefully acknowledge D. Robinson of the Advanced Photon Source (APS) in the Argonne National Laboratory for assistance with the high-energy X-ray diffraction measurements, D. Fielden, M. Bharadwaj and G. Jones of The University of Tennessee (UT) for the technical support. ZT very much appreciates C.P. Chuang, J.E. Spruiell, and C.D. Lundin of UT, J.S. Hou of the Chinese Academy of Sciences, J.W. Qiao of Taiyuan University of Technology China, M.C. Gao of the National Energy Technology Laboratory (NETL) for helpful discussions. Work at AFRL was supported through the United States Air Force (USAF) Contract no. FA8650-10-D-5226 . Research sponsored by the Oak Ridge National Laboratory (ORNL)’s Shared Research Equipment (ShaRE) User Program, which was sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy (C.M. Parish). The authors very much appreciate M.K. Miller of ORNL for his efforts on the atom-probe tomography (APT).
Keywords
- Crack initiation
- Heat treatment
- High-entropy alloys
- Microstructures
- Tensile properties
- Thermodynamic modeling