Advances in Multi-Principal Elements Alloys X: Structures and Modeling: Structures and Characterization I
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, Alcoa Technical Center

Tuesday 2:30 PM
March 1, 2022
Room: 251B
Location: Anaheim Convention Center

Session Chair: Takeshi Egami, The University of Tennessee, Knoxville; Jian-Min Zuo, University of Illinois Urbana-Champaign

2:30 PM  Invited
Chemical Randomness and Lattice Distortions in Multi-principal Elements Alloys: Advances in Characterization: Jian Min Zuo1; Haw-Wen Hsiao1; Yu-Tsun Shao1; Yang Hu1; Qun Yang2; 1University of Illinois; 2ShanghaiTech University
    Multi-Principal Elements Alloys (MPEAs) are a new class of materials that are chemically concentrated in the phase spaces of largely unexplored. Since their discovery in 2004, these alloys have demonstrated remarkable chemical and physical properties that have attracted tremendous interest. However, their atomic structure and strengthening mechanisms are shrouded in mystery. The two fundamental aspects of MPEAs, namely chemical randomness and possible short range ordering and lattice distortions, have been suggested, but so far there are no conclusive experimental evidences. Here, we report on advances in analytical scanning transmission electron microscopy (STEM) that combines chemical analysis with the analysis of electron diffuse scattering using nanodiffraction. Using this approach, we determine lattice distortions in both MPEAs and high entropy alloys. The experimental evidences provide a comprehensive picture of nanoscopic structural and chemical fluctuations in these advanced alloys.

2:50 PM  
Metastability and Phase Selection in High Entropy Alloys: Sebastian Kube1; Sungwoo Sohn1; Pamela Banner1; David Uhl2; Amit Datye1; Suchismita Sarker3; Apurva Mehta3; Jan Schroers1; 1Yale University; 2Southern Connecticut State University; 3SLAC National Accelerator Laboratory
    High Entropy Alloys (HEAs) span a vast composition space, across which single-phase solid solutions (SPSS) can form at varying degrees of metastability. We argue that metastable SPSS form through polymorphic solidification upon rapid cooling. To quantify a HEA’s metastability, we propose the critical cooling rate of SPSS formation R_C_SPSS, which is analogous to R_C_Glass for glass formation. On this unified basis, we compare multicomponent alloys by their metastability and tendency to form SPSS or glasses, which is determined by the underlying atomic dispersity. We explore this space experimentally using combinatorial co-sputtering coupled with high-throughput EDX and synchrotron XRD. Within our new data set, which comprises ~15,000 ternary and quinary compositions based on 20 different elements, we find simple, yet insightful quantitative models for solid solution and glass formation.

3:10 PM  Invited
TEM Study of a Refractory Complex Concentrated Alloy with BCC/B2 Microstructure: Jean-Philippe Couzinie1; Milan Heczko2; Veronika Mazanova2; Oleg Senkov3; Rajarshi Banerjee4; Maryam Ghazisaeidi2; Michael Mills2; 1Université Paris Est and Department of Materials Science and Engineering, The Ohio State University; 2The Ohio State University; 3Air Force Research Laboratory; 4University of North Texas
    Among the most promising structural materials, refractory complex concentrated alloys (RCCAs) are currently of major importance as they could retain high mechanical properties beyond 1000°C. Promising compositions are found in alloy systems for which the ordered B2 phase is present, as a matrix or precipitates together with a disordered BCC phase. However, some basic challenges have still to be addressed. This is especially the case regarding the impact of such complex microstructure in BCC/B2 RCCAs on deformation mechanisms. To this aim, the talk will give some insights into the microstructure and the deformation processes of an alloy Al-Nb-Ta-Ti-V-Zr after compressive testing at 25°C and 600°C. Detailed transmission electron microscopy analysis of the phases and also of the defects governing the plastic deformation will be reported and discussed.

3:30 PM  Invited
NOW ON-DEMAND ONLY - Design of High Temperature RCCAs Using Ordered Thermally Stable Structures: Jaimie Tiley1; Soumya Nag1; Ke An1; Ercan Cakmak1; Jonathan Poplawsky1; Raymond Unocic1; Sriswaroop Dasari2; Rajarshi Banerjee2; 1Oak Ridge National Laboratory; 2University of North Texas
    Meta-stable and heterogenous structures within refractory complex concentrated alloys (RCCAs) provide creative new strengthening mechanisms for material use within extreme environments. The use of ordered structures and chemical segregation coupled with heterogenous phase nucleation sites produced through processing allows increased tailoring of specific microstructures. This research investigates the impact of Ti and Al additions and thermo-mechanical-processing on the formation of heterogeneous B2 and related ordered structures within a HfNbTaZr equi-atomic alloy, including the subsequent impact on mechanical properties. Potential compositions for a new candidate high temperature RCCA were determined through validated CALPHAD models. Samples were produced and evaluated by coupled characterization using neutron and X-ray diffraction, atom probe tomography, transmission electron microscopy, and mechanical testing at elevated temperatures. Atom probe tomography was conducted at ORNL’s Center for Nanophase Materials Science, a Department of Energy Office of Science user facility.

3:50 PM Break

4:10 PM  Invited
In-situ 4D-STEM Imaging of the Synergistic Deformation Mechanisms Responsible for the Fracture Resistance in CrCoNi: Yang Yang1; Sheng Yin2; Qin Yu2; Ruopeng Zhang2; Mark Asta2; Robert Ritchie2; Andrew Minor2; 1The Pennsylvania State University; 2LBNL
    High- and medium-entropy alloys (HEAs and MEAs) have shown excellent fracture toughness, especially under cryogenic temperatures. It was previously shown by in-situ TEM that a synergy of multiple deformation mechanisms including dislocations and twinning is responsible for such outstanding mechanical performance. On the other hand, the existence of chemically local ordering, i.e., short-range-order (SROs), has recently been directly imaged by multiple research groups. However, the interplay between SROs and the mechanical performance in HEAs and MEAs still remains unclear. Here, we applied a new technique, namely in-situ four-dimensional scanning transmission electron microscopy (in-situ 4D-STEM), to study the mechanical deformation in CrCoNi MEA at nanometer resolution in real-time. We directly probed the critical role of SROs on the tuning of nano-structural deformation mechanisms. With further insights from molecular dynamics simulations, our study identified the critical steps in the synergistic deformation mechanisms responsible for the fracture resistance in CrCoNi.

4:30 PM  Invited
Effective Atomic Size in Multi-principal Element Alloys: Takeshi Egami1; 1University of Tennessee
    Various properties of multi-principal element alloys (MPEAs) are attributed to local lattice distortion caused by mixing atoms with different sizes. Whereas the idea of atomic size has been very widely and successfully used in many fields, it is not so obvious how it should be defined, given that the electron density is continuous. It is usually defined empirically to explain the bond length, assuming transferability from a system to another. However, there is a serious problem with transferability, because chemistry can affect the effective size. It is well-known in chemistry that the ionic size depends on valence. In the same way charge transfer affects the atomic size in MPEAs. We discuss the results of the DFT calculation on the atomic-level pressure to determine the effective atomic size in various 3d-transition metal MPEAs, focusing on the effect of charge transfer. The work was supported by the NSF, DMREF-1921987.