High Entropy Alloys V: Alloy Development and Applications II
Sponsored by: TMS Structural Materials Division, TMS Functional 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; Suveen Nigel Mathaudhu, University of California Riverside; Xie Xie, The University of Tennessee, Knoxville; Gongyao Wang, Alcoa Technical Center; E-Wen Huang, National Chiao Tung University

Tuesday 2:00 PM
February 28, 2017
Room: 32B
Location: San Diego Convention Ctr

Session Chair: Suveen Nigel Mathaudhu, University of California, Riverside; Yong Liu, Central South University

2:00 PM  Invited
Precipitation Strengthening Effects in Powder Metallurgical High Entropy Alloys: Yong Liu1; Bin Liu1; Qihong Fang2; C.T. Liu3; 1Central South University; 2Hunan University; 3City University of Hong Kong
    Powder metallurgy becomes more and more important in processing high entropy alloys (HEAs). Through casting, inhomogeneous and coarse microstructures usually are unavoidable, because HEAs usually contain complex alloying elements. The presentation introduced our recently progress in processing HEAs with interstitial and heavy elements. FeCoCrNiAl0.5 HEA was alloyed with different amount of carbon and Mo. HEA powders prepared by the gas atomization method were hot extruded and heat treated, and long HEA bars with very homogeneous microstructures were obtained. Both the precipitation of carbides and intermetallic phases were investigated by using high resolution TEM. The results indicated that HEAs have high tensile strength and reasonable ductility, and both properties can be flexibly adjusted by controlling the precipitation process. Finally, the mechanism of microstructural evolution and the plastic deformation were discussed. In general, powder metallurgy can be considered as a promising way for preparing large-sized HEAs with high mechanical properties.

2:20 PM  Invited
Synthesis and Characterization of Nanostructured Magnetic High Entropy Alloys: Trevor Clark1; Christian Roach1; Suveen Mathaudhu1; 1University of California Riverside
    High entropy alloys (HEAs) have demonstrated a variety of beneficial properties owing to their unique microstructural compositions and features. Research has predominantly focused on mechanical property improvements via the refinement of grains to the nanoscale. At the same time, advances have been made in the design and synthesis of nanostructured permanent magnets for energy-efficiency applications such as compact electrical motors. In this presentation, we report new results on the synthesis and processing of nanostructured CoCrFeMnNi HEA magnets produced via mechanical alloying and powder consolidation. Results will probe the inter-relationships between the synthesis approach and chemical compositions, the resulting grain sizes and phase distributions, and strength properties. Lastly, magnetic properties will be reported and compared with conventional permanent magnet nanocomposites.

2:40 PM  
Adaption of Metal Injection Molding to Quinary High Entropy Alloys: Arnaud Grimonprez1; Julia Wagner2; Volker Piotter1; Alexander Kauffmann1; Yizhou Chen1; Martin Heilmaier1; 1Karlsruhe Institute of Technology (KIT); 2University of Stuttgart
    Metallic alloys with multiple principal elements are promising candidates for different industrial applications, due to their new and unexpected properties. For industrial use, however, fast and reliable production routes are necessary. Metal injection molding (MIM) is known to be an efficient method to produce near net shape components ranging from mm to meter. Since the physical and chemical environments of high entropy alloy systems are fundamentally different from those of conventional alloy systems production routes must be adapted. In this contribution we present mechanical tests on Co20Cr20Fe20Mn20Ni20 at.% specimens produced by MIM. The developed feed-stock of the gas-atomized material was directly molded into tensile test specimen shaped molds. The microstructure evolution was characterized in all production steps. Differences in both the mechanical behavior and the microstructure compared to results observed on material with the same chemical composition, which was synthesized by classical metallurgical methods will be discussed in detail.

3:00 PM  
Design of Novel Precipitate Strengthened Al-Co-Cr-Fe-Nb-Ni High-entropy Alloys: Martin Detrois1; Stoichko Antonov1; Sammy Tin1; 1Illinois Institute of Technology
    A series of non-equiatomic Al-Co-Cr-Fe-Nb-Ni high-entropy alloys, with varying levels of Co and Nb, were investigated in an effort to obtain microstructures similar to conventional Ni-base superalloys. Although elevated levels of Nb and Co were observed to increase the solvus temperature of the γ’ precipitates, they also promoted the formation of Nb-rich intermetallic phases that formed during solidification and remained undissolved during homogenization. Lowering the content of either the Nb or Co prevented the formation of undesirable phases and resulted in finer γ’ precipitates while lowering the Co content alone resulted in a higher number and density of the γ’ precipitates. Various aging treatments were studied and allowed to control the size and distribution of the strengthening phase that formed during cooling. Results from the microstructural characterization and mechanical property assessments of these two-phase high-entropy alloys will be presented and discussed.

3:20 PM  Invited
Design of High Entropy Alloys for Turbine Applications: Ida Berglund1; James Saal1; Jason Sebastian1; Gregory Olson1; 1QuesTek Innovations
    Integrated Computational Materials Engineering (ICME) tools are being developed for the design of high entropy alloys (HEAs) for extreme environments, such as industrial gas turbine (IGT) blades. HEAs, particularly those containing refractory elements, have the potential to surpass Ni-based superalloy performance in IGT applications by enabling higher operating temperature. The current work has focused on construction and validation of a large CALPHAD thermodynamic database (QT-HEA) specifically designed for HEAs, as conventional CALPHAD databases are not sufficiently accurate at equiatomic compositions. QT-HEA is based on experimental data as well as exhaustive high-throughput density functional theory (DFT) calculations of the mixing enthalpies for all combinatorically possible FCC and BCC ternary solid solutions. Novel HEA compositions have been identified using QT-HEA and experimentally verified by lab-scale alloy synthesis and characterization. A processing-structure-property framework has been created, and ongoing work focuses on the development of property models to enable the design of HEAs.

3:40 PM Break

4:00 PM  Invited
Combinatorial Design of High Entropy Alloys: Discovery of a Novel Single BCC Solid Solution: Pradeep Konda Gokuldoss1; 1Max Planck Institute for Iron Research GmbH
    A family of Fe-Mn containing high entropy alloy thin film spread is produced by combinatorial DC magnetron sputtering using four individual metal targets. Compositional spread over wide range of concentrations (15-30 at.% of each element) for all possible alloy combinations were achieved. High throughput property characterization employing grazing incidence XRD, atom probe tomography, transmission kikuchi diffraction were performed to map the phase formation as a function of local chemical concentrations. Results indicate that a highly stable non-refractory single BCC phase solid solution was achieved over a wide range of compositions. The as-formed single BCC solid solution exhibits outstanding mechanical and magnetic properties.

4:20 PM  
Design of "High Entropy Alloys" (HEA) with Optimal Combinations of Stability, Density, Strength and Ductility: Edern Menou1; Isaac Toda-Caraballo2; Emmanuel Bertrand1; Gérard Ramstein1; Pedro Rivera-Díaz-del-Castillo2; Franck Tancret1; 1Université de Nantes; 2University of Cambridge
    New “high entropy alloys” have been designed by genetic algorithm multi-objective optimisation relying on (i) both computational thermodynamics (Thermo-Calc CALPHAD software) and a Gaussian process model combining most of the physical criteria available in the literature to guide the formation of a single phase, (ii) the minimisation of density, (iii) the maximisation of yield stress using a solid solution hardening model, and/or (iv) the maximisation of ductility based on a CALPHAD estimate of the stacking fault energy. Some of the designed alloys have been cast, homogenised at high temperature and characterised by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and Vickers hardness testing. Among others, we have obtained a single phase alloy with a density of 5.25 g/cm3 with a hardness in excess of 6 GPa (indicating a yield stress around 2000 MPa), which could be even improved by applying additional thermo-mechanical treatments to refine grain size.

4:40 PM  
Fabrication of High-entropy Refractory Metal Carbides: Tyler Harrington1; Joshua Gild2; Jian Luo3; Cormac Toher4; Pranab Sarker4; Stefano Curtarolo5; Kenneth Vecchio3; 1University of California San Diego; 2Materials Science and Engineering Program, UC San Diego; 3Department of NanoEngineering and Materials Science and Engineering Program, UC San Diego; 4Department of Mechanical Engineering and Materials Science, Duke University; 5Materials Science, Electrical Engineering, Physics, and Chemistry, Duke University
    Bulk samples of three equiatomic, five-component, high-entropy refractory carbides were fabricated using a combination of high-energy ball milling, spark plasma sintering, and hot pressing. Each of the complex carbide compositions, including (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)C, (Hf0.2Nb0.2Ta0.2Ti0.2V0.2)C, and (Nb0.2Ta0.2Ti0.2V0.2W0.2)C demonstrated virtually single-phase, solid-solution compounds and were sintered to greater than 95% theoretical density. Microstructure homogeneity was improved by subsequent 2500°C heat treatment. To select likely candidate compositions to form an entropy-stabilized material, the different configurations should have similar energies to increase the number of thermodynamically accessible states. A partial occupation method was implemented within AFLOW to automate the generation and calculation of the different configurations. The energy distributions were then used to construct a descriptor to predict the formation of these high-entropy materials. CALPHAD results were found to agree with the configuration energy range descriptor for each composition, and these carbides exhibited broad, single-phase solubility across each system, making processing easier.

5:00 PM  Invited
The Oxidation of an Equimolar FeCoNiCrMn High-entropy Alloy in CO/CO2 Mixed Gases at 973K (700oC): Wu Kai1; Fu-Pen Cheng1; Rong-Tan Huang1; Leu-Wen Tsay1; Ji-Jung Kai1; 1National Taiwan Ocean University
    The oxidation behavior of an equimolar FeCoNiCrMn high-entropy alloy was studied in various CO/CO2 mixed gases over the oxygen partial pressure range from 5.03  10-16 to 5.03  10-14 Pa at 973K (700oC). The results showed that the oxidation kinetics of the alloy followed the parabolic rate law, regardless of oxygen pressure. The oxidation rate constants increased with increasing oxygen partial pressure, indicative of a typical oxide scale exhibiting a p-type semiconductivity. The scales formed on the alloy consisted mostly of MnO and minor amount of (Mn,Cr)3O4.

5:20 PM  
Carbides-induced Hardening of CoCrFeMnNi Family of HEAs: Adrianna Lozinko1; Michal Mroz1; Fares Haddad1; Anna Fraczkiewicz1; 1MINES St-Etienne
    CoCrFeMnNi alloys constitute a well-documented family of single-phased HEAs. Further optimization of these materials needs to use combined mechanisms of hardening; especially, precipitation hardening should bring strong effects. However, the predicted and already confirmed slow-down of diffusion in HEA may be a limiting factor for such an approach. In this work, the possibilities and conditions of carbides precipitation in CoCrFeMnNI are discussed. Alloys containing 200 ppm of carbone have been doped with niobium or tanatalum. Precipitation heat treatments have been chosen according to ThermoCalc predictions and their effects checked by experimental analyses. Niobium carbide (NbC) has been shown to ensure intergranular hardening as well as for limit efficiently the grain growth in recrystallized material.