High Entropy Alloys VIII: Synthesis and Alloy Development
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
February 27, 2020
Room: Marina Ballroom F
Location: Marriott Marquis Hotel
Session Chair: William Curtin, Swiss Federal Institute Of Technology; Wai-Yim Ching, University Of Missouri-Kansas City
8:30 AM Invited
Theory for Yield Strength of BCC HEAs: William Curtin1; Francesco Maresca1; 1Epfl Sti Igm Lammm
The collective fluctuations in solute/dislocation interaction energies in dilute and HEA BCC alloys lead to the spontaneous energy-lowering formation of a kinked/wavy structure over characteristic lengths ζc,screw(edge). Dislocation motion is determined by the energetics at scale ζc. New general theories for both screw and edge motion in BCC alloys starting from this basic phenomenon are presented. The screw theory accurately predicts strength in Nb-Mo binary, and suggests some existing HEAs are pseudo-binaries. The edge theory shows that edges can control strengthening, especially at high temperatures. The edge theory explains (i) the exceptional retention of strength measured in MoNbTaW and MoNbTaVW at temperatures up to 1900K, (ii) why the V-containing alloy is stronger, and (iii) trends in other recent data. A simplified analytic form enables efficient computationally-guided design of new alloy compositions across the entire family of Cr-Mo-Nb-Ta-V-W-Hf-Ti-Zr BCC HEAs. Several new compositions are proposed and discussed.
8:50 AM Invited
High Entropy Alloy Nanomaterials as Filler Materials for Brazing Ni-based Superalloys: Anming Hu1; Benjamin Nielsen1; Denzel Bridges1; Raymond Xu1; Zhili Feng1; Peter Liaw1; 1University of Tennessee
It is possible to design high entropy alloys (HEA) as brazing filler materials (BFM) with compatible metallurgical properties and the thermal expansion of coefficient to the based materials while without using melting point depressants (MPDs). However, the melting point of high entropy alloys is limited due to multiple design principles of high entropy alloys. In this work, we try to overcome this barrier through fabricating nanoscale high entropy alloys. We compared three methods to synthesize HEA nanomaterials: wet-chemistry, ball milling and electrical wire explosion. The microstructure, defects, thermal properties of these HEA nanomaterials are characterized and the fundamentals for brazing applications, such as the melting, wettability and solidification, element diffusions for vacuum brazing and laser brazing of Inconel 718 are investigated. The feasibility of HEA nanomaterials as brazing filler materials is also investigated through computational modeling using a phase field theory.
9:10 AM Invited
Electronic Descriptors for Designs of Chemically Complex Transition-metal Alloys: Yong-Jie Hu1; Xiaofeng Qian2; Liang Qi1; 1University of Michigan; 2Texas A&M University
Chemically complex alloys, such as high entropy alloys and concentrated solid solution alloys, have many potential applications, but it is difficult to find quantitative parameters to describe and predict their structures and properties. Based on tight-binding scheme, we recently discovered a general correlation between electronic descriptors of local densities of states (LDOS), especially d-band LDOS, and the solute-defect interaction energies in binary alloys of body-centered-cubic refractory metals (such as W and Ta) with transition-metal substitutional solutes. Our correlation model can be used as a screening tool to study the solute segregation in general crystalline defects. We extend and modify these electronic descriptors for chemically complex alloys. The correlations between fundamental mechanical alloy properties, such as elastic moduli, stacking fault energies and surface energies, and possible electronic descriptors are explored. These general electronic descriptors can be used to speed up the search of chemically complex alloys with improved hardness and ductility.
9:30 AM Invited
Formability Enhancement of High-entropy Alloy by Manipulation of Stacking Fault Energy: Jeong-Won Yeh1; Chanyang Kim1; Kook Noh Yoon1; Hyun Seok Oh1; Myoung-Gyu Lee1; Eun Soo Park1; 1Seoul National University
The rapid evolution of modern industries demands advanced materials exhibiting greatly improved performances. Recently, the development strategies of high entropy alloy (HEA) have shown great potential to resolve these challenges with their inherent mechanisms of damage tolerance under extreme environments such as high stress, high temperature and high radiation flux. However, in order to commercialize HEAs, the formability enhancement should be considered because the ability is closely related to plastically deform without being damaged. However, there is very little attention up to date to evaluate formability in these materials. Herein, we systematically demonstrate the effect of stacking fault energy (SFE) on the formability in FCC HEAs. As a results, the Forming Limit Diagram of FCC HEAs with different SFEs are carefully constructed by both experiments and numerical simulations. Indeed, this result would offer a essential guideline how to design HEAs with optimal shape as well as properties for harsh environments.
9:50 AM Invited
Exceptional Strength-ductility Combination in an FCC Based High Entropy Alloy: Bharat Gwalani1; Sriswaroop Dasari2; Vishal Soni2; Shivakant Shukla2; Abhinav Jagetia2; Priyanshi Agrawal2; Rajiv Mishra2; Rajarshi Banerjee2; 1Pacific Northwest National Laboratory; 2University of North Texas
We designed a novel precipitation strengthened high entropy alloy (HEA) composition based on high fraction of L12 precipitates strengthening a face-centered cubic (FCC) matrix, using an iterative CALPHAD-based approach. By optimizing the alloying additions, the FCC + L12 phase field was stabilized to 1150°C while maintaining a high L12 phase fraction at 1000°C. Thermo-mechanical processing resulted in concurrent recrystallization and L12 precipitation, with the alloy retaining a homogeneous sub-micron grain size along with a high density of nano-lamellar L12 precipitates. This microstructure exhibits high YS strength ~1650 MPa with a tensile ductility ~15%, and an ultimate tensile strength ~1800 MPa. Our results show that the combination of overall compositional optimization of the alloy coupled with the nano-lamellar morphology of the L12 ordered precipitates help in maintaining a reasonably high ductility within such a fine-grained precipitation strengthened HEA. This is the best strength-ductility combination reported till now in any bulk HEA.
10:10 AM Break
10:30 AM Invited
Electroplating Nanocrystalline Medium and High-entropy Alloys: Lianbo Wang1; Michel Hache1; Yu Zou1; 1University of Toronto
Compared with typical nanocrystalline (nc) metals and alloys, nc high-entropy alloys (HEAs) exhibit exceptional mechanical properties with satisfied thermal stability. Typical methods for producing nanocrystalline HEAs usually requires severe mechanical deformation. Upon heating, grain size grows rapidly, limiting their applications at elevated temperatures. Here, we investigate a series of equiatomic binary NiCo, ternary NiCoFe, NiFeCr, and quaternary NiCoFeCu nanocrystalline alloys, produced using electrodeposition. The alloys were subsequently processed with heat treatment at temperatures in the range 573-823 K. Nanoindentation were applied to identify the temperature dependency of mechanical properties. Our study demonstrates a scalable method for producing high-strength and thermally stable HEAs.
10:50 AM Invited
Thermal Transport Calculation of High Entropy Alloys for Thermoelectric Applications: Seungha Shin1; Md Abdullah Al Hasan1; Jiaqi Wang1; Yu-Kai Weng1; Dustin Gilbert1; 1University of Tennessee
Desirable thermal transport and phase stability of High Entropy Alloys (HEAs) are critical for aerospace, energy, transportation, and manufacturing applications which require excellent performance, reliability, and efficient high-temperature thermoelectric properties in extreme operating conditions. In our study, for effective thermal transport control in HEA, we investigated three topics: (1) mass and interaction mismatch effect on the thermal conductivity and phonon density of states (PDOS). Thermal conductivity and PDOS can be altered by various mass distribution, resulting from various scattering rate of phonons; (2) disorder quantification in HEA. Structural and compositional disorder reduces thermal conductivity and thus the quantification is crucial for the selection of elements of HEA; (3) prediction of phase formation of different HEA’s. Various thermoelectric properties (i.e., Seebeck coefficient, electrical conductivity, and figure-of-merit etc.) are unraveled and a model for prediction of HEA are developed.
11:10 AM Invited
Theory of Formation of High Entropy Alloys for Biomedical Applications: Wai-Yim Ching1; Saro San1; Jamieson Brechtl2; Ridwan Sakidja3; Miqin Zhang4; Peter Liaw5; 1University of Missouri; 2 University of Tennessee; 3Missouri State University; 4University of Washington; 5University of Tennessee
High entropy alloys (HEAs) have attracted a great deal of attention. The fundamental theory and computational modeling of HEAs is still not fully developed. We propose a new approach based on building relatively large supercells of HEAs, and calculate their electronic structure and bonding to provide critical parameters, the total bond order density (TBOD) and the partial bond order density (PBOD). They avoid the use of a pure geometric description and implicitly include the entropy effect by virtual random distribution of atoms. Results from the DFT calculations on 13 bio-compatible HEAs (TiNbTaV, TiNbTaZr, TiNbTaZrMo, HfNbTaV, NbTaTiVZr, TiZrHfNbTa, TiHfNbTa, TiZrHfTa, TiZrHfNb, TiZrNbHfTa, ZrNbMoHfTa, TiZrNbMoHf, and TiNbMoHfTa) with supercells of 250 atoms in the cubic BCC lattice are presented. The calculated elastic and mechanical properties are in good agreement with the experimental data and correlate with the TBOD. For TiNbTaZrMo, introduction of porosity leads to a significant reduction in the Young’s modulus.