Advances in Multi-Principal Elements Alloys X: Alloy Development and Properties: Structures and Mechanical Properties I and 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; Jennifer Carter, Case Western Reserve University; Srivatsan Tirumalai; Xie Xie, FCA US LLC; Gongyao Wang, Globus Medical

Wednesday 8:30 AM
March 2, 2022
Room: 251A
Location: Anaheim Convention Center

Session Chair: Veerle Keppens, University of Tennessee; Lei Lu, Chinese Academy of Sciences; Michael Widom, Carnegie Mellon University; Liang Jiang, Yantai University

8:30 AM  Invited
Synthesis and Properties of High Entropy Oxide Ceramics: Veerle Keppens1; 1University of Tennessee
    Utilizing entropy as the driving force for stabilizing oxide materials offers a path for the discovery of innovative compounds with unique structure-property relations. However, the intrinsic disorder and highly localized chemical environments of HEOs bring along new challenges. In order to shed light on the complexities associated multi-cation oxides, we have initiated a systematic study of polycrystalline HEO samples across multiple crystal systems. This work expands the multi-component concept to new compositions and crystal systems and investigates properties of materials across multiple crystal systems, including spinel, perovskite, and Ruddlesden-Popper multi-component materials.

8:50 AM  Invited
Gradient Cell Structured High-entropy Alloy with Superior Mechanical Behavior: Lei Lu1; Qingsong Pan1; liangxue Zhang1; Rui Feng2; Peter K Liaw3; 1Chinese Academy of Sciences; 2Oak Ridge National Laboratory; 3The University of Tennessee
    Most multicomponent high-entropy alloys (HEAs) are inevitably subject to losing ductility with increasing strength similar to conventional materials. Here, we controllably introduce a gradient nano-scaled dislocation-cell-structure in one stable single-phase Al0.1CoCrFeNi HEA, which results in significantly enhanced strength with exceptional ductility at ambient and at liquid nitrogen temperatures, and is superior to its counterparts with either homogeneous or heterogeneous structures. The sample-level structural-gradient structure with length scales spanning 6 orders of magnitude, the chemical features of the HEA and the nanoscaled dislocation cells with low-angle boundaries collectively contribute to a unique deformation mechanism associated with the formation of a high density of tiny stacking-faults and twins. Our findings offer a new promising pathway for improving the mechanical properties of materials through gradient dislocation structure.

9:10 AM  Invited
Dynamic Deformation Behaviors in Single BCC Phase Refractory High-entropy Alloys: Chanho Lee1; Mathew Hayne1; Peter Liaw2; Nan Li1; Saryu Fensin1; 1Los Alamos National Laboratory; 2The University of Tennessee
    Refractory high-entropy-alloys (RHEAs) show remarkable mechanical properties, such as high yield strength with significant softening resistance. Due to these excellent mechanical properties during quasi-static deformation, the RHEAs have attracted significant attention as potential metallic materials for the high temperature applications. To broaden the applications of RHEAs, the dynamic deformation behaviors/mechanisms and microstructural evolution at elevated temperature should be investigated and revealed. In this study, we have studied the deformation behaviors of single-BCC-phase NbTaTiV and NbTaTiV RHEAs during quasi-static and dynamic deformations (strain rate between 10-4 to 2,500 s-1). The high strain-rate compression tests were performed by Split Hopkinson Pressure Bar (SHPB) techniques. It is found that the NbTaTiV shows no working hardening/softening at elevated temperatures and the yield strength does not strongly depend on strain-rates. The evolutions of microstructure during dynamic deformation at elevated temperatures were systematically investigated by electron back-scattered diffraction (EBSD) to further verify the deformation mechanisms.

9:30 AM  Invited
A High-throughput Strategy to Study Phase Stability, Microstructure Development and Mechanical Properties in Complex Concentrated Alloys: Mu Li1; Zhaohan Zhang1; Katharine Padilla1; Rohan Mishra1; Katharine Flores1; 1Washington University in St. Louis
    The design of high entropy alloys often focuses on identifying equiatomic solid solution alloys; expanding these complex concentrated alloys (CCAs) to include multiphase microstructures offers the opportunity to further enhance and control properties. Designing such multiphase CCAs requires the ability to efficiently survey compositional space for phases and microstructures of interest using integrated experimental and computational methods. Here, we present a laser deposition-based high-throughput method to synthesize compositional and microstructural libraries, and compare the experimentally observed structures with predictions based on first-principles calculations. We have selected Nb-V-Zr as a model base, and evaluate the influence of additional refractory alloying elements, with a focus on near-equiatomic fractions. Mechanical behavior as a function of composition and microstructure is evaluated via nanoindentation at temperatures up to 800C. This work provides guidelines for predicting compositional effects on microstructure and properties, which will accelerate the design of CCAs for high-temperature applications.

9:50 AM Break

10:10 AM  Invited
Small-scale Deformation Behavior of Multi-principal Element Alloys: Shristy Jha1; Saideep Muskeri1; Sundeep Mukherjee1; 1University of North Texas
    Multi-principal element alloys (MPEAs) have attracted widespread interest due to their exceptional properties at multiple length-scales. Small-scale mechanical behavior of several single-phase and complex MPEAs was investigated. Strain rate sensitivity and strain gradient plasticity was measured for fundamental understanding of deformation mechanism. The nano-mechanical behavior and twinned microstructure was explained by low stacking fault energy. Phase-specific response was evaluated for multi-phase MPEAs using micro-pillar compression and micro-cantilever bending tests to explain their simultaneous high strength and good ductility.

10:30 AM  
Composition- and Grain-size-dependent Hydrogen Uptake and Its Effect on Plastic Deformation of Face-centered Cubic High-entropy Alloys: Yakai Zhao1; Jeong-Min Park2; Upadrasta Ramamurty1; Jae-il Jang2; 1Nanyang Technological University; 2Hanyang University
    An intriguing yet overlooked issue in hydrogen effects on high-entropy alloys (HEAs) is the hydrogen uptake and its effects in the fcc HEAs having very different fractions of defects. Therefore, in this work, the effect of marked change in grain size from coarse-grained to nanocrystalline on the hydrogen absorption and plastic deformation behavior of two HEAs, viz. equiatomic CoCrFeNi and CoCrFeMnNi, were investigated. Thermal desorption analysis of the hydrogen-charged samples proved that grain boundaries act as hydrogen traps and thus largely increase the hydrogen contents in the nanocrystalline samples. The parameters for the thermally activated deformation from nanoindentation rate-jump tests suggest enhanced lattice friction by hydrogen, leading to a reduction in activation volume and thus modification of the plastic deformation processes. The results are discussed in two aspects, viz. the effect of grain size and chemical composition on the hydrogen-affected plastic deformation.