Progress towards Understanding the Synthesis and Behavior of Metals Far from Equilibrium: A SMD Symposium Honoring Enrique Lavernia on the Occasion of His 60th Birthday: High-entropy Alloys
Sponsored by: TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Composite Materials Committee
Program Organizers: Haiming Wen, Missouri University of Science and Technology; Suveen Mathaudhu, Colorado School of Mines; Yuntian Zhu, City University of Hong Kong; Manoj Gupta, National University of Singapore; Kaka Ma, Colorado State University; Troy Topping, California State University Sacramento; Yizhang Zhou, University of California, Irvine; Joshua Yee, Sandia National Laboratories; Dalong Zhang, Pacific Northwest National Laboratory; Yaojun Lin, Wuhan University of Technology; Fei Chen, Wuhan University of Technology
Wednesday 2:00 PM
February 26, 2020
Room: 31B
Location: San Diego Convention Ctr
Session Chair: Haiming Wen, Missouri University of Science and Technology; Yaojun Lin, Wuhan University of Technology
2:00 PM Invited
Predictive Multiphase Evolution in Al-containing High-entropy Alloys: Louis Santodonato1; Peter Liaw2; Raymond Unocic3; Hongbin Bei3; James Morris4; 1Advanced Research Systems; 2The University of Tennessee; 3Oak Ridge National Laboratory; 4Ames Laboratory
The mixing of five or more elements, in near- equimolar concentrations, to form disordered substitutional solid solutions is a central feature of the class of materials known as high-entropy alloys (HEAs). It is now becoming clear that the most promising HEAs for practical applications may actually be those, which undergo phase transformations and separations during cooling. The present talk describes an approach to guide the development of multi-phase HEAs, using a simple Monte Carlo model with parameters derived from first-principles calculations. These high-throughput simulations are compared with neutron scattering, in situ microscopy, and calorimetry measurements. We demonstrate that the present technique captures not only the qualitative features, but also gives accurate quantitative results for the intermetallic phase formation and microstructure evolution of the Al-containing HEAs. Work is underway to generalize the approach and study a wider range of compositions
2:30 PM Invited
Hierarchical Microstructural Paradigms for Simultaneous Enhancement of Strength and Ductility: Rajiv Mishra1; 1University of North Texas
Strength plays an important role in structural efficiency of materials and is a key driver for the strength-limiting design and fatigue-limiting design values. Nanocrystalline and ultrafine grained alloys possess significant strength because of grain boundary strengthening. However, they lack uniform ductility and work hardening. To simultaneously enhance strength and ductility, approaches that balance blockage of dislocations and strain hardening rate while delaying the onset of failure mechanisms are needed. Some recent results on transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) high entropy alloys (HEAs) will be presented to highlight the potential of achieving exceptional work hardening rate in ultrafine HEAs. As a result of higher work hardening, the TRIP and TWIP HEAs exhibit enhanced fatigue behavior. The enhancement in fatigue behavior is linked with delayed crack nucleation. In TRIP HEAs, the crack growth is retarded by transformation in the localized region of crack.
3:00 PM
Microstructural Evolution and Mechanical Behavior of an AlCoCrCuFeNi High Entropy Alloy during Non-equilibrium Powder Metallurgical Processing: Baolong Zheng1; Benjamin MacDonald1; Zhiqiang Fu1; Yizhang Zhou1; Enrique Lavernia1; 1University of California, Irvine
Significant improvements in materials properties have been achieved by processing the materials under far-from-equilibrium (or non-equilibrium) conditions, such as rapid solidification (RS), cryogenic severe plastic deformation (SPD), and fast field assisted sintering (FFAS). A combination of a series of non-equilibrium processes, including gas atomization (GA), cryomilling (CM) and spark plasma sintering (SPS) was employed in this research to fabricate a nano-crystalline (NC) multi-phase AlCoCrCuFeNi High Entropy Alloy (HEA). The non-equilibrium microstructural evolution was investigated by using SEM, TEM/HRTEM, and XRD techniques, and revealed nano-scale deformation structures including dislocation tangles and deformation bands. In this presentation, the influence of processing on grain size and phase evolution is reported and discussed. The influence of the non-equilibrium nature of GA, CM, and SPS processing on the grain refinement, and its effects to the mechanical properties are discussed in an effort to highlight the underlying fundamental phenomena associated with non-equilibrium processing and microstructural evolution.
3:20 PM
Development of New Magnesium Based Medium Entropy Alloys: Microstructure and Mechanical Properties: Khin Tun1; Tirumalai S. Srivatsan2; Amit Kumar3; Manoj Gupta1; 1National University of Singapore (NUS); 2The University of Akron; 3Glocal University
In the present study, low-density multicomponent alloys based on the Mg-Al system were investigated in order to develop advanced lightweight alloys. For the current alloy development, the alloy design was based on multi-element alloying approach to increase the mixing entropy in order to be categorized as medium entropy alloys (MEAs). In new alloys developed in this study, the concentration of each alloying element remained ≥ 5 at % with Mg (60 and 70 at.%) as dominant base material. The calculated mixing entropy in the new alloys was ≥ 1R (R is gas constant, 8.314 J/K mol), qualifying them as medium entropy alloys. The new magnesium based medium entropy alloys, Mg60Al20Cu10Zn5Mn5 and Mg70Al10Cu10Zn5Mn5, were synthesized using disintegrated melt deposition technique. Following synthesis, characterization studies were done on the materials. Particular emphasis was placed to examine and understand the microstructural development and resultant influence of microstructure on mechanical properties.
3:40 PM Break
4:00 PM Invited
Experimental Observations of CALPHAD Predicted Phases in High-entropy Alloys: Reza Abbaschian1; Nicholas Derimow1; Benjamin MacDonald1; Enrique Lavernia1; 1University of California
We present the latest experimental observations and CALPHAD predictions of phase formation in AlCrFeNiMo0.3, CoCrCuNi, and CoCrCuMnxTi high-entropy alloys (HEAs). Thermo-Calc predictions for these alloys were made using the TCHEA3 database, while the experimental observations consisted of microstructural analysis from arc-melting, electromagnetic levitation melting, and neutron imaging experiments. The latter was utilized for in-situ imaging of liquid phase separation in CoCrCu, and remixing into a single liquid with the addition of Ni to form molten CoCrCuNi. These observations as well as formation of face-centered cubic phases were in agreement with those predicted. Similarly, for the CoCrCuMnxTi alloys, calculations predicted the presence of the experimentally observed hexagonal Laves C14 phase as well as the Cu-rich FCC interdendritic phase. On the other hand, arc-melting of AlCrFeNiMo0.3 showed the presence of a stable liquid miscibility gap, while calculations predicted a liquid miscibility gap at very large supercoolings.
4:30 PM
AlFeNiTi Compositionally Complex Alloys: Daniel Goodelman1; Andrea Hodge1; 1University of Southern California
Compositionally complex alloys (CCAs) have attracted considerable attention in the past decade due to their excellent mechanical properties, such as high hardness, improved damage tolerance, high thermal stability, and improved wear resistance over conventional alloys. In this study, CCAs were synthesized by employing magnetron sputtering techniques to observe the composition space of the AlFeNiTi CCA family, with the goal of developing a crystallographic gradient across the face of the sputtered substrates. Characterization techniques such as X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive X-ray spectroscopy were employed to observe the composition space, microstructure, and morphology of these sputtered materials.
4:50 PM
Microstructure and Mechanical Properties of a Nanostructured High Entropy Alloy Processed via Cryogenic Rolling: Yaojun Lin1; Zhigang Yan2; Fei Chen1; 1Wuhan University of Technology; 2Yanshan University
As a new class of materials, high entropy alloys (HEAs) are attracting considerable interest worldwide. In this talk, we report microstructure and tensile properties of a nanostructured equiatomic HEA Fe25Co25Cr25Ni25 produced via cryogenic rolling with a thickness reduction ratio of approximately 90% followed by annealing. Microstructures in as-rolled and annealed materials are studied using transmission electron microscopy (TEM), high resolution TEM and transmission Kikuchi diffraction. The microstructures including nano-sized grains, and nanoscale twinning and lamellar structure, as well as characteristic crystalline defect configurations, are presented. The mechanical properties of the HEA processed are measured via tensile testing. Our results reveal that heterogeneous microstructures can be attained during annealing, and that the nanostructured HEA exhibits an acceptable combination of strength and ductility. Based on the results in the present work, we discuss the future directions to increase ductility of, and to achieve excellent combination of strength and ductility in, nanostructured HEAs.