High Entropy Alloys IX: 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; Srivatsan Tirumalai; Xie Xie, FCA US LLC; Gongyao Wang, Globus Medical
Tuesday 2:00 PM
March 16, 2021
Room: RM 9
Location: TMS2021 Virtual
Session Chair: Robert Ritchie, University of California, Berkeley; Michael Widom, Carnegie Mellon University
2:00 PM Invited
Electronic Effects on the Mechanical Properties of HEA: Takeshi Egami1; 1University of Tennessee
When different elements are alloyed into a high-entropy alloy (HEA) electronic wavefunctions of atoms hybridize each other to form the electronic band structure. Consequently, electrons redistribute themselves and cause charge transfer from one element to the other. This charge transfer has profound effects on local mechanical response, including dislocation pinning. We describe this effect through the ab initio DFT calculation of the atomic-level stresses. The results satisfactorily explain the mechanical strength as well as the extent of local lattice distortion of HEAs. We show that the atomic-level pressure defines the effective atomic size through the Eshelby theory of inclusion. The effective atomic size depends on local chemistry, and it can be significantly different from the usual atomic size. Therefore, it reflects local chemical short-range order. This work is supported by the NSF through DMREF-1921987.
2:25 PM Invited
An Averaged Cluster Approach to Include Chemical Short Range Order in First Principles Calculations with Application to High Entropy Alloys: Vishnu Raghuraman1; Yang Wang1; Michael Widom1; 1Carnegie Mellon University
The single-site Korringa-Kohn-Rostoker Coherent Potential Approximation (KKR-CPA) ignores short range ordering present in disordered metallic systems. We establish a new technique to fix this shortcoming by embedding an averaged cluster that displays chemical short range order (SRO). The degree of SRO can be tuned by externally defined order parameters. The validity of this method is demonstrated by applying it to two alloy systems - the CuZn body centered cubic (BCC) solid solution, and AlCrTiV, a four-element BCC high entropy alloy. We demonstrate that in each case the resulting total energies select preferred patterns of B2-like chemical occupation. In the case of the high entropy alloy we show that the electronic density of states favors patterns of chemical order that place the Fermi energy in a pseudogap.
2:50 PM
Faulting-mediated Plasticity in a CoCrNiW Complex Concentrated Alloy: Shaolou Wei1; Cem Tasan1; 1Massachusetts Institute of Technology
Crystalline defects are of fundamental importance in understanding and thereby tailoring the macroscopic mechanical responses of complex concentrated alloys (CCAs). Particularly in microstructural metastability engineering, appreciable interest has aggregated in transformation-induced plasticity or twinning effect. However, the inherent operative unit, stacking faults, have not yet drawn abundant attention. By investigating a CoCrNiW CCA, we will reveal a lesser-explored deformation “faulting” response. Through coupled in-situ synchrotron and ECCI experiments, we will show that the nucleation of extensive stacking faults is acting as the major plasticity carrier within this CCA, providing macroscopic strain hardenability. We will demonstrate that this sort of faulting mechanism is largely ascribed to a negative stacking fault energy, for which our in-situ ECCI experiment will provide a direct validation. Broader insights into the role of multi-layer generalized stacking fault energy landscape will also be discussed to complement the current thermodynamic-guided design strategy of metastable CCAs or high-entropy alloys.
3:10 PM Invited
Unique Deformation Behavior in the NbTaTiV Refractory High-entropy Alloy: Chanho Lee1; George Kim2; Yi Chou3; Brianna Musicó1; Michael Gao4; Ke An5; Gian Song6; Yi-Chia Chou3; Veerle Keppens1; Wei Chen2; Peter Liaw1; 1University of Tennessee; 2Illinois Institute of Technology; 3National Chiao Tung University; 4National Energy Technology Laboratory/Leidos Research Support Team; 5Oak Ridge National Laboratory; 6Kongju National University
Single-phase solid-solution refractory high-entropy-alloys (HEAs) show remarkable mechanical properties, such as high yield strength with significant softening resistance at elevated temperatures. Hence, the in-depth study of the deformation behavior for body-centered-cubic (BCC) refractory HEAs is a critical issue to explore the uncovered/unique deformation mechanisms. We have investigated the elastic- and plastic-deformation behaviors of a single BCC NbTaTiV refractory HEA at elevated temperatures, using integrated experimental efforts and theoretical calculations. The in-situ neutron-diffraction results reveal a transition of the elastic-deformation feature from isotropic to anisotropic modes at elevated temperatures. The single-crystal elastic-moduli and macroscopic Young’s, shear and bulk moduli were determined from the in-situ neutron diffraction, showing the great agreement with first-principles calculations, machine-learning, and resonant-ultrasound spectroscopy results. Furthermore, the edge-dislocation-dominant plastic-deformation behavior, which is different from conventional BCC alloys, have been quantitatively described by the Williamson-Hall plot profile modeling. These results are further experimentally verified by the high-angle-annular-dark-field scanning-transmission-electron-microscopy (STEM).
3:35 PM Invited
Unprecedented Supercritical Elasticity in NiCoFeGa Multi-principal-element Alloys: Haiyang Chen1; Yan-Dong Wang1; Yang Ren2; 1University of Science and Technology Beijing; 2Argonne National Laboratory
We recently discovered a new type elasticity: supercritical elasticity (SCE), in NiCoFeGa multi-principal-element alloys [Chen et al., Nature Materials, (2020). https://doi.org/10.1038/s41563-020-0645-4]. In this talk, we will show that by tuning the element concentrations to nearly equal fractions, the alloys exhibit a large elasticity up to 15.2% strain, with non-hysteretic mechanical responses, a small temperature dependence and high-energy-storage capability and cyclic stability over a wide temperature and composition range. We found that the SCE is ultimately related to a novel microstructure consisting of atomic-level entanglement of ordered and disordered crystal structures, which can be manipulated to tune the SCE. We will discuss the impact of this work on the future exploitation of elastic strain engineering and development of related functional materials for a wide variety of high-performance engineering applications, ranging from deep-space and deep-sea exploration to intelligent robotics.
4:00 PM Invited
Influence of Ductile Multicomponent Intermetallic Phase on Mechanical Behavior in High-entropy Alloys: Rui Feng1; You Rao2; Huamiao Wang3; Yan Chen1; Chuan Zhang4; Maryam Ghazisaeidi2; Ke An1; Peter Liaw5; 1Oak Ridge National Laboratory; 2The Ohio State University; 3Shanghai Jiao Tong University; 4Computherm, LLC; 5The University of Tennessee, Knoxville
Ordered intermetallics consist of two or more metals bonded with specific stoichiometries that possess stable high-temperature properties due to the strong atomic bonds. These strong directional bonds cause room-temperature brittleness due to a limited number of slip systems and poor grain-boundary cohesion. The concept of high-entropy alloys (HEAs) provides new opportunities to tune materials’ intrinsic characteristics to achieve outstanding properties. Here we designed a multicomponent NiAl-type B2 phase strengthened HEA, in which the multicomponent B2 phase not only contributes to the strengthening but also accommodates the plastic deformation with the matrix. The deformation behavior of the multicomponent B2 intermetallic is studied by in-situ neutron diffraction, transmission-electron microscopy, Monte-Carlo simulation, and elastic-visco-plastic self-consistent modeling. The study suggests that dislocation slip in the multicomponent intermetallic phase becomes easier than those of traditional intermetallics. The present work offers insights into the design of ductile multicomponent intermetallic alloys with the retention of high strengths.