HEA 2023: Performance in Extreme Environments III
Program Organizers: Andrew Detor, DARPA/DSO; Amy Clarke, Los Alamos National Laboratory
Wednesday 1:40 PM
November 15, 2023
Room: Riverboat
Location: Omni William Penn
Session Chair: Philseok Kim, ARPA-E, Department of Energy
1:40 PM Introductory Comments
1:45 PM Cancelled
Defects in High Entropy Alloys: A Real Cocktail Effect: Simon Middleburgh1; Christopher Moore1; Jack Wilson1; Alexander Lin-Vines1; 1Bangor University
The behavior of point defects in high entropy alloys differ from standard alloy systems due to the distribution of stabilities, readily assessed using modelling techniques such as atomic scale modelling. Not only are the formation of defects altered, but so too are the migration and recombination of defects initiated due to athermal effects such as radiation damage. A range of atomic scale techniques shall be presented that impact a various characteristics of high entropy alloys in use, including their use as corrosion barriers, neutron shielding materials and hydrogen storage materials. The ability to understand these atomic scale processes aids in the design of bespoke alloys, fit for specific purposes.
2:05 PM
Combined Experimental and Numerical Investigation of Ductile Fracture in the Cantor Alloy: Ahmed Ataya1; Joshua Herrington1; Shi-Hoon Choi2; Amine Benzerga1; 1Texas A&M University; 2Sunchon National University
The ductile fracture of the CoCrFeMnNi high-entropy alloy was investigated. Round notched and unnotched bars were deformed to fracture in tension in order to determine the influence of stress triaxiality. Some bars were interrupted near macrocrack initiation. Fractographic analysis reveals a failure mechanism dominated by void nucleation at second-phase particles, followed by growth to coalescence. Dimple size measurements were acquired in-plane and depth-wise using a profilometer. The finite element method was utilized to analyze notched bars using constitutive relations of porous material plasticity. With nearly no fitting damage parameters, the constitutive model allowed for a good prediction of failure strains. Furthermore, unit cell calculations were carried out for a periodic array of voids in a J2 matrix under remote triaxial loadings after calibrating the plasticity parameters. This simple approach allowed for a good prediction of the fracture locus as well as the deformed void dimensions.
2:25 PM
A CALPHAD Based Approach for Designing Precipitation-hardened High-entropy Alloys: Diego Santana1; Claudio Kiminami1; Amy Clarke2; Michael Kaufman2; Francisco Coury1; 1Universidade Federal de São Carlos; 2Colorado School of Mines
Designing precipitation-hardened high-entropy alloys with good mechanical properties is challenging due to the complexity introduced by composition and heat treatment temperatures. To address this, thermodynamic calculations based on the CALPHAD method were employed to analyze 11,235 compositions of Cr-Co-Ni-Al-Ti alloys. By applying specific filtering criteria, the remaining alloys were evaluated to estimate their solid solution hardening and maximum precipitation hardening contributions to yield strength. To validate the methodology, three alloys were selected, processed, and subjected to microstructural and mechanical characterization techniques. The results were compared with predictions made using CALPHAD and mathematical modeling, revealing a positive qualitative agreement. This approach shows promising potential in effectively identifying and developing new precipitation-hardened alloys with improved mechanical properties.
2:45 PM
Self-healing and Machinable Refractory High-entropy Alloys for Energy and Aerospace Applications: Sal Rodriguez1; 1Sandia National Laboratory
Lathing, filing, drilling, slicing, polishing, and RHEA-to-RHEA welding were performed on SPS- and LENS-manufactured test pieces. RHEA combinations with the highest degree of machinability tended to be more ductile, but had a lower yield strength, and vice-versa. Of the selected RHEA combinations, most survived the extensive machining at room temperature (RT), though a few shattered. An analysis of the experimental data provides several insights regarding the continued development and improvement of higher-strength machinable compositions at RT.NbTaVW RHEA test pieces were manufactured via LENS to test for self-healing, and were subsequently irradiated at the Ion Beam Laboratory. High energy Au ions at 2.8 MeV at a dose of 1x1014 ions/cm2 resulted in 0.9 displacements per atom, while a dose of 1x1015 ions/cm2 resulted in 9 DPA. The average measured nanoindentation hardness of the irradiated RHEA increased 5 to 24%, comparatively less than Inconel 718 and 316 stainless-steel samples.