High Entropy Alloys IX: Alloy Development and Properties: Alloy Development and Application IV
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

Thursday 8:30 AM
March 18, 2021
Room: RM 10
Location: TMS2021 Virtual

Session Chair: Wei Chen, Illinois Institute of Technology; Jian Luo, University of California, San Diego


8:30 AM  Invited
From High-entropy Ceramics (HECs) to Compositionally Complex Ceramics (CCCs): Jian Luo1; 1University of California, San Diego
    This talk will first review our recent studies of high-entropy ceramics (HECs), including high-entropy borides [Scientific Reports 2016], perovskite [Scripta 2018] and fluorite [JECS 2018] oxides, and silicides [J. Materiomics 2019], as well as single-phase high-entropy intermetallic compounds (aluminides) that bridge high-entropy metals and ceramics [Science Bulletin 2019]. Up to 2020, nearly all work of HECs has focused on five-component, equimolar compositions. We proposed a step forward to expand HECs to compositionally complex ceramics (CCCs) to include medium-entropy and non-equimolar compositions; see a perspective in J. Mater. Sci. 55:9812 (2020). For example, we found better thermally-insulating yet stiff CCCs in non-equimolar YSZ-like fluorite CCCs [JECS 2020] and in ordered pyrochlores with substantial size disorder [Scripta 2020]. It is demonstrated that medium-entropy ceramics can prevail over their high-entropy counterparts. The diversifying classes of CCCs provide even more possibilities than HECs to tailor the composition, defects, disorder/order, and, consequently, various properties.

8:55 AM  
Direct Production of High Entropy Alloy Powders: Jawad Haidar1; 1Kinaltek Pty Ltd.
    A novel method is presented for direct production of multi-component alloy powders using aluminothermic reduction of metal compounds based on Fe, Cr, Co, Ni, Cu, Zn, V, Nb, Mo, Sn, Sb, Ta, W, Ag and Al. The method provides for a mixture of precursor chemicals to be mixed and reacted exothermically with Al under controlled conditions using a control powder. Reduction is carried out in a controlled manner to regulate reaction rates and prevent excessive rise in the temperature of the reactants and the reaction products. Alloying additives such as C, B and Si can be included. Results are presented for direct production of HEA alloys based on Co, Cr, Fe, Ni, Al and Nb.

9:15 AM  
Hierarchical Eutectoid Nano-lamellar Decomposition in an Al0.3CoFeNi Complex Concentrated Alloy: Sriswaroop Dasari1; Bharat Gwalani1; Abhishek Sharma1; Vishal Soni1; Abhinav Jagetia1; Stephane Gorsse2; Rajarshi Banerjee1; 1University of North Texas; 2University of Bordeaux, France
    Guided by solution thermodynamics, phase decomposition has been tuned in the same Al0.3CoFeNi complex concentrated alloy (CCA), to develop a novel eutectoid-like nano-lamellar (FCC+L12) / (BCC+B2) microstructure versus a coarser scale FCC+B2 microstructure. This novel eutectoid nano-lamellar microstructure results from the complex interplay between Al-mediated lattice distortion (due to its larger atomic radius) in a face-centered cubic (FCC) CoFeNi solid solution, and a chemical ordering tendency leading to precipitation of ordered phases such as L12 and B2. The eutectoid microstructure is a result of solid-state decomposition of the FCC matrix and therefore distinct from the commonly reported eutectic microstructure in HEAs which results from solidification. The nano-lamellar microstructure exhibits a tensile yield strength of 1074 MPa with a tensile ductility ~ 8%, while the more damage-tolerant FCC+B2 microstructure, exhibits high tensile yield stress (~900 MPa) with appreciable tensile ductility (>20%).

9:35 AM  Invited
Data-driven Design of Refractory High-entropy Alloys: Wei Chen1; George Kim1; Chanho Lee2; Peter Liaw2; 1Illinois Institute of Technology; 2University of Tennessee
    The material-design strategy of combining multiple elements in near-equimolar ratios has spearheaded the emergence of high-entropy alloys (HEAs), an exciting class of materials with exceptional engineering properties. While random mixing has been widely assumed in multi-principal element solid solutions, both experimental and computational evidence suggests short-range ordering (SRO) exists in many solid-solution HEAs. We employed an integrated first-principles and experimental approach to understand the thermodynamic effects of SRO in the refractory NbTaTiV and NbTaTiVZr HEA systems. The existence of SRO produces distinct lattice distortion features in these HEAs and affects their mechanical properties. The fundamental understanding of SRO and lattice distortion is coupled with high-throughput first-principles calculations to design refractory high-entropy alloys.

10:00 AM  
Accelerated Alloy Development and Characterization of Compositionally Complex Alloys via High-throughput Methods: Phalgun Nelaturu1; Michael Moorehead1; Thien Duong2; Michael Niezgoda1; Adrien Couet1; Kumar Sridharan1; Santanu Chaudhuri2; Dan Thoma1; 1University of Wisconsin; 2Argonne National Laboratory
    Additive manufacturing via directed energy deposition was used as a high-throughput technique to synthesize compositionally complex alloys in the Cr-Fe-Mn-Ni quaternary system. In situ alloying by controlled flow of four elemental powder hoppers permitted more than 100 bulk samples with different compositions to be synthesized within a week. Compositional control to within ±5 at% was achieved. Re-melting passes between each printing layer reduced the area fraction of unmelted powder in the build to <0.2%. The alloys were heat treated in a high-throughput fashion (50 alloys at a time) which involved homogenization at 1000 °C for 24 hours, followed by aging at 700 °C for 24 hours. The alloys were characterized by automated EDS and XRD, SEM imaging, and microhardness. The experimental results were coupled with CALPHAD modeling to expand the thermodynamic databases and build a physics-based model that could predict the hardness of these alloys based only on the composition.

10:20 AM  
Nanostructured Oxide-dispersion-strengthened High-entropy Alloys: Xiang Zhang1; Fei Wang1; Xueliang Yan1; Xing-Zhong Li1; Khalid Hattar2; Bai Cui1; 1University of Nebraska-Lincoln; 2Sandia National Laboratories
    A nanostructured oxide-dispersion-strengthened (ODS) CoCrFeMnNi high-entropy alloy (HEA) has been synthesized by mechanical alloying process. The thermal stability, including the grain size and phase composition of the HEA matrix, as well as the particle size of oxide dispersions, were carefully investigated by electron microscopy characterizations after annealing at 900 oC. The limited grain growth may be attributed to Zener pinning of intergranular yttria dispersions that impede the grain boundary mobility. The hardness of nanostructured ODS CoCrFeMnNi HEA is 2.7 times higher than CoCrFeMnNi HEA without yttria dispersions. This research implies that the combination of ODS and HEA concepts may provide a new design strategy for the development of thermally stable nanostructured alloys for extreme environments.

10:40 AM  
A High-throughput Strategy to Study Phase Stability and Mechanical Properties in Nb-Ti-V-Zr: Mu Li1; Zhaohan Zhang1; Arashdeep Thind1; Guodong Ren1; Rohan Mishra1; Katharine Flores1; 1Washington University in St. Louis
    The current design strategy for refractory complex concentrated alloys (RCCAs) is mainly focused on identifying equiatomic solid solution alloys with high ductility. Information about competing intermetallic phases and the dependence of their stability on composition is still lacking. In this work, we examine phase stability in Nb-Ti-V-Zr as a function of composition. Starting with an equiatomic NbVZr alloy, we observe two Laves phases, cubic C15 and hexagonal C14, in addition to the BCC majority phase. First principles calculations predict the stable composition for each phase, which are consistent with experimental observations. We then use direct laser deposition to rapidly synthesize Nb-Ti-V-Zr compositional libraries, and use these to map the crystal structures, microstructures and mechanical properties as a function of composition. Experimental results are compared with first-principles calculations. This work provides guidelines for predicting compositional effects on microstructure and properties, which will accelerate the design of RCCAs for high-temperature applications.