High Entropy Alloys IX: Alloy Development and Properties: Structures and Mechanical Properties II
Sponsored by: TMS Functional Materials Division, TMS Structural Materials Division, TMS: Alloy Phases Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Peter Liaw, University of Tennessee; Michael Gao, National Energy Technology Laboratory; E-Wen Huang, National Chiao Tung University; Srivatsan Tirumalai; Xie Xie, FCA US LLC; Gongyao Wang, Globus Medical

Wednesday 2:00 PM
March 17, 2021
Room: RM 10
Location: TMS2021 Virtual

Session Chair: Saryu Fensin, Los Alamos National Laboratory; Nan Li, Los Alamos National Laboratory

2:00 PM  Invited
Dynamic Properties of a High Entropy Alloy -- FeCrMnNi: Michelle Hawkins¹; Robert Hixson²; Jonathan Gigax²; Nan Li²; Sarah Thomas¹; Saryu Fensin²; ¹Mission Support and Test Services, LLC; ²Los Alamos National Laboratory
    High Entropy Alloys represent a new class of materials that possess an ideal combination of high strength and ductility and may be candidate materials that can withstand high amounts of damage before failure, under extreme conditions. To this end, a series of shock/spall loading experiments were conducted on an Fe/Cr/Mn/Ni HEA to assess not only its Equation of State (EOS) but also its resistance to nucleate damage and failure. A single stage light gas gun was used to conduct a series of flyer plate symmetric impact experiments coupled with recovery of the samples for post-mortem microstructural analysis to obtain fundamental understanding regarding the damage morphology. Our results show that the measured EOS for this alloy was in reasonable agreement with an estimated Hugoniot. Additionally, the spall strength of these alloys was found to vary between 1.4-1.9 GPa within the same plate but was comparable to other iron based conventional alloys.

2:20 PM
Effect of Cooling Rate on the High Strain Rate Deformation of Dual-phase High Entropy Alloy: Samrat Tamuly¹; Saurabh Dixit¹; V Parameswaran¹; Prasenjit Khanikar¹; ¹Indian Institute of Technology Guwahati
    A novel high entropy alloy Al0.65CoCrFe2Ni comprising of both FCC and BCC phases is designed, and fabricated through two liquid state techniques. One alloy sample is processed using a vacuum induction melting technique in an industrial-scale melting furnace. The other alloy sample is fabricated in a lab-scale copper suction casting facility having a considerably higher cooling rate of solidification. Split Hopkisnon pressure bar test is carried out under compressive loading at strain rate of ~2000s-1 for both the industrial-scale induction melted alloy and lab-scale suction cast alloy samples. The effect of cooling rate on both alloy samples under high strain rate deformation is analyzed by observing their strain hardening behavior and strain rate sensitivities. The predictability of high strain rate behavior of the high entropy alloy will also be examined using Johnson-Cook modeling.

2:40 PM
Mechanical and Elastic Behavior as Well as Microstructural Response of NbTaTiV and NbTaTiVZr as a Function of Strain Rate: Mathew Hayne¹; Saryu Fensin¹; Tarik Saleh¹; Chanho Lee²; Peter Liaw²; ¹Los Alamos National Laboratory; ²The University of Tennessee
    High entropy alloys (HEAs) represent a rapidly expanding field in metallurgy due to their unique ability to meet mechanical design criteria over a range of deformation rates. To date, most studies evaluating the mechanical properties of these alloys have focused on quasi-static compression testing, with only a few studies being conducted to understand the response at high strain rates. In this study, the mechanical properties of two refractory high-entropy alloys (RHEA), NbTaTiV and NbTaTiVZr, have been investigated using resonant ultrasound spectroscopy (RUS), quasi-static compression, and high strain-rate compression via Split Hopkinson pressure bar (SHPB). Pre- and post-deformation microstructures were examined using electron microscopy to help elucidate the mechanisms leading to both materials exhibiting an increase in the yield stress as a response to the increased strain rate.

3:00 PM
Deformation Mechanism and Microstructural Evolution in Al_0.4CoCrFeNi High Entropy Alloy: Anumat Sittiho¹; Jadzia Graves¹; Sanjit Bhowmick²; Indrajit Charit¹; Rajiv Mishra³; ¹University of Idaho; ²Bruker; ³University of North Texas
    A high entropy alloy Al_0.4CoCrFeNi produced by casting is the focus of the study to understand the deformation behavior and microstructure evolution under two types of mechanical testing: macro-compression and micropillar compression. Scanning electron microscopy and transmission electron microscopy were used to study the microstructural characteristics in the as-cast and deformed specimens to identify the micromechanical processes involved. Micropillars were fabricated using a focused ion beam scanning electron microscope. Micropillar compression testing of [001] oriented crystals exhibited significant strain hardening rate while almost negligible strain hardening rate in [111] oriented crystals was obtained. However, the yielding flow stress is found to be much higher for the [111] oriented crystals as opposed to [001] ones. The deformation characteristics of the macro-compression tests is discussed in light of the results obtained from the micropillar compression tests.

3:20 PM
On the Phase Stability, Mechanical Properties, and Deformation Mechanisms of the Equiatomic CrFeNi Medium-entropy Alloy: Mike Schneider¹; Guillaume Laplanche¹; ¹Ruhr-Universitat Bochum
    The CrFeNi medium-entropy alloy, due to its compositional simplicity and its single-phase character, constitutes a missing link between binary and more complex engineering alloys such as austenitic stainless steels and Fe-based superalloys. In this study, heat treatments at various temperatures revealed that CrFeNi forms a stable FCC solid solution above ~1250 K. Compression and tensile tests were carried out for recrystallized FCC microstructures with different grain sizes between 77 K and 873 K. To reveal the active deformation mechanisms in CrFeNi, additional tensile tests were interrupted at different strains followed by transmission electron microscopy analyses. In all cases, deformation was accommodated by dislocation glide at low strains, whereas twinning was additionally triggered above a critical resolved shear stress, which was roughly temperature independent and compares well with modeling predictions.