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Title: Radiation behavior of high-entropy alloys for advanced reactors. Final report

In the first task, we have demonstrated the radiation damage and the recrystallization behaviors in multicomponent alloys through molecular-dynamics simulations. It is found that by alloying with atoms of different sizes, the atomic-level strain increases, and the propensity of the radiation-induced crystalline to amorphous transition increases as the defects cluster in the cascade body. Recrystallization of the radiation induced supercooled or glass regions show that by tuning the composition and the equilibrium temperature, the multicomponent alloys can be healed. The crystalline-amorphous-crystalline transitions predict the potential high radiation resistance in multicomponent alloys. In the second task, three types of high-entropy alloys (HEAs) were fabricated from AlCoCrFeNi and AlCuCrFeNi quinary alloys. Hardness and reduced contact modulus were measured using nanoindentation tests. Heavy ion irradiation were performed using 10 MeV gold and 5 MeV nickel to study radiation effects. Al0.5CrCuFeNi2 shows phase separation upon the presence of copper. Both hardness and contact modulus exhibit the same trend as increasing the applied load, and it indicates that excessive free volume may alter the growth rate of the plastic zone. The as-cast Al0.1CoCrFeNi specimen undergone the hot isostatic pressing (HIP) process and steady cooling rate which mitigate the quenching effect. The swelling behavior was characterizedmore » by the atomic force microscopy (AFM), and the swelling rate is approximately 0.02% dpa. Selected area diffraction (SAD) patters show irradiation-induced amorphization throughout the ion projected range. Within the peak damage region, an amorpous ring is observed, and a mixture of amorphous/ crystalline structure at deeper depth is found. The Al0.3CoCrFeNi HEAs shows good radiation resistance up to 60 peak dpa. No voids or dislocations are observed. The crystal structures remain face-centered-cubic (FCC) before and after 5 MeV Ni irradiation. Higher dpa might be required to study defects formation mechanisms. In the third task, all the constituent binary and ternary systems of the Al-Co-Cr-Fe-Ni system were thermodynamically modeled within the whole composition range. Comparisons between the calculated phase diagrams and literature data are in good agreement. The multi-component thermodynamic database of the Al-Co-Cr-Fe-Ni system was then obtained via extrapolation. The current Al-Co-Cr-Fe-Ni thermodynamic database enables us to carry out the calculations of phase diagrams, which can be used as useful guidelines to identify the Al-Co-Cr-Fe-Ni HEAs with desirable microstructures. In the fourth task, we discuss how as-cast and homogenized phases can be identified, what phases are usually found in the as-cast and homogenized conditions, and what the thermodynamics and kinetics of phase transformations are in the AlCoCrFeNi HEA. The microstructure and phase composition were studied in as-cast and homogenized conditions. It showed the dendritrical structure in the as-cast condition consisting primarily of a nano-lamellar mixture of A2 [disorder body-centered-cubic (BCC)] and B2 (ordered BCC) phases, in addition to a very small amount of A1 [disorder face-centered-cubic (FCC)] phases. The homogenization heat treatment resulted in an increase in the volume fraction of the A1 phase and formation of a Sigma phase. Tensile properties in as-cast and homogenized conditions are reported at 700 °C. Thermodynamic modeling of non-equilibrium and equilibrium phase diagrams for the AlCoCrFeNi HEA gave good agreement with the experimental observations of the phase contents. The reasons for the improvement of ductility after the heat treatment are discussed.« less
Authors:
 [1] ;  [1] ;  [2] ;  [2] ;  [1]
  1. Univ. of Tennessee, Knoxville, TN (United States)
  2. CompuTherm, LLC, Madison, WI (United States)
Publication Date:
OSTI Identifier:
1214790
Report Number(s):
DOE/NEUP--11--3196
11-3196; TRN: US1500412
DOE Contract Number:
AC07-05ID14517
Resource Type:
Technical Report
Research Org:
Univ. of Tennessee, Knoxville, TN (United States); CompuTherm, LLC, Madison, WI (United States)
Sponsoring Org:
USDOE Office of Nuclear Energy (NE). Nuclear Energy University Programs (NEUP)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; FCC LATTICES; BCC LATTICES; ATOMIC DISPLACEMENTS; DISLOCATIONS; DUCTILITY; PHASE DIAGRAMS; MEV RANGE 01-10; ALUMINIUM ALLOYS; COBALT ALLOYS; COPPER ALLOYS; CHROMIUM ALLOYS; IRON ALLOYS; NICKEL ALLOYS; HOT PRESSING; COPPER; GOLD IONS; NICKEL IONS; HARDNESS; MIXTURES; SWELLING; DIFFRACTION; EQUILIBRIUM; EXTRAPOLATION; IRRADIATION; MOLECULAR DYNAMICS METHOD; COMPARATIVE EVALUATIONS; HEAT TREATMENTS; CRYSTAL DEFECTS; DEPTH; MICROSTRUCTURE; RECRYSTALLIZATION; AMORPHOUS STATE; PHASE TRANSFORMATIONS; COOLING; GLASS; SUPERCOOLING; KINETICS; QUENCHING; RINGS; COMPUTERIZED SIMULATION; STRAINS; THERMODYNAMICS; VOIDS; PHYSICAL RADIATION EFFECTS; SIZE; CHEMICAL COMPOSITION; TEMPERATURE DEPENDENCE; STATIC LOADS; CRYSTAL STRUCTURE; BINARY ALLOY SYSTEMS; TERNARY ALLOY SYSTEMS; PHASE STUDIES; LAMELLAE; TEMPERATURE RANGE 0400-1000 K