High Entropy Alloys V: Mechanical and Other Properties
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

Wednesday 2:00 PM
March 1, 2017
Room: 32A
Location: San Diego Convention Ctr

Session Chair: Sundeep Mukherjee, University of North Texas; Qingfeng Xing, Ames Laboratory

2:00 PM  Invited
Weldability and Welding Solidification of an HEA Alloy: Joshua Burgess1; Carl Lundin2; Zhi Tang3; Peter Liaw2; 1GE Power; 2The University of Tennessee; 3Alcoa
    Weldbility assessments of HEA's must be addressed early on in order to highlight any potential problems in initial fabrication and for repair welding of service exposed components of HEA type alloys . An initial study was undertaken to investigate the GTA autogenous welding behavior of an Al0.1 CoCrFeNi alloy in the hipped and annealed condition. The welds showed typical FCC weldability with no welding defects generated in any weld region including the fusion zone and Heat-Affected Zone (HAZ). This study portends good fabricability for these FCC multicomponent compositions.

2:20 PM  Invited
Bringing High-entropy Alloys Close to High-temperature Applications: Single Crystal Growth, Microstructure Characterization, and Mechanical Tests: Qingfeng Xing1; Haoyan Diao2; Deborah Schlagel1; Trevor Riedemann1; Peter Liaw2; Thomas Lograsso1; 1Ames Laboratory; 2University of Tennessee - Knoxville
    A brittle Cr-rich phase segregates at grain boundaries of polycrystalline high-entropy alloys (HEAs) and degrades their creep performance at elevated temperatures. To understand the intrinsic creep-deformation mechanisms, high-quality and large-size HEA single crystals are fabricated by Bridgman growth. The unseeded growth yields an Al0.3CoCrFeNi single crystal allowing [1 0 0] and [1 1 0] rods of 6 mm diameter and 25 mm length to be machined from it for in situ deformation observation by neutron diffraction and creep tests. To obtain [1 1 1] and [3 1 1] rods, seeded Bridgman growth are used to make a larger single-crystal ingot with [1 1 0] along the longitude direction. The mechanical properties and detailed microstructures of the single-crystal HEAs are investigated and compared with their counterparts, polycrystalline Al0.3CoCrFeNi HEAs. This prototype study will accelerate the application of HEAs at high temperatures and shed light on the future design of creep-resistant HEAs.

2:40 PM  
Degradation Behavior of High Entropy Alloys – Corrosion, Erosion, and Wear: Ayyagari Aditya1; Sundeep Mukherjee1; 1University of North Texas
    High entropy alloys (HEAs) show superior resistance to surface degradation by corrosion and oxidation and are potentially transformative for critical structural applications. However, there is limited understanding of corrosion, erosion, and wear behavior of these alloys in dry and simulated sea water (SSW) environments. We report on the wear and corrosion mechanisms for several canonical HEAs in dry and SSW environments. Adhesive wear was the dominant wear mechanism involved in the degradation process. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements were performed to understand the corrosion mechanisms. Raman and auger surface spectroscopy were employed to identify the corrosion products and passivation layers. The severity of corrosion assisted wear behavior changed with the test conditions in the HEA systems. This study demonstrates the improved surface degradation resistance of HEAs, which may lead to adoption of these materials for structural applications in marine environments.

3:00 PM  
Investigation of Equiatomic AlNbTiMoV and AlNbTaTiV Alloys for High Temperature Applications: Anne Denquin1; Arnaud Grimonprez1; Agnès Bachelier-Locq1; 1Onera
    The objective of this study is the evaluation of high entropy alloys for aeroengines applications up to 1000°C. AlNbMoTiV and AlNbTiTaV equiatomic compositions have been produced by arc melting in the form of 250g ingots. As-cast microstructure and phase transformations during heat treatments have been investigated through SEM, DRX and TEM, revealing the ordered character of the matrix of both alloys and the extensive precipitation of the σ phase at 1000°C in the Ta containing composition. Mechanical properties have been evaluated through compression and creep-compression tests up to 800°C. Both alloys show yield strengths above 1200MPa at room temperature and serrations on the deformation curves at 500°C, indicative of a PLC-type effect. Results of creep tests will be presented and the results of mechanical investigations discussed in term of potential of these alloys for high temperature applications.

3:20 PM  
Irradiation Resistance of Low Activation High Entropy Alloys: David Armstrong1; John Waite1; Angus Wilkinson1; 1University of Oxford
    It has been suggested that High Entropy Alloys (HEAs) have intrinsically high resistance to irradiation damage due to their inherently random atomic arrangement, however experimental validation is currently lacking. A single phase equiatomic BCC Titanium-Vanadium-Zirconium-Hafnium-Tantalum alloy (produced by arc meting), was irradiated using V+, Si+ and Ta+ ions to peak damages of 0.2dpa, 6dpa and 66dpa, with maximum damage depths between 300nm and 1.3μm. The hardening after irradiation was studied using nanoindentation. In the 0.2dpa and 6dpa implantations no hardening of the HEA alloy was measured. This compares with hardening from 2.1GPa to 3.1GPa in a Vanadium sample at 0.2dpa damage and 38 to 42GPa in a Silicon Carbide control at 3.5dpa damage. At 66dpa the hardness increase in the HEA was ≈0.4GPa compared to a 3GPa increase in a control Tantalum sample. This proves the inherent irradiation damage resistance of this HEA alloy at nuclear reactor relevant damage levels.

3:40 PM Break

4:00 PM  
Weldability of Single-phase and Multi-phase High Entropy Alloys: Zhenggang Wu1; Stan David1; Zhili Feng1; Hongbin Bei1; 1Oak Ridge National Laboratory
    To investigate the effects of alloying and phases on the weldability on the high-entropy alloys (HEAs), we selected two model alloys, namely, the single phase (fcc) CrCoFeMnNi and two-phase (fcc + hcp) Fe50Mn30Co10Cr10 to conduct autogenous welding experiments using lab-scaled materials. The phase stability, segregations, and the sensitivity to thermal cracks after welding thermal cycles were investigated by using microstructural observation. Mechanical testing on the weldments is also conducted to determine the possible degradation of the mechanical properties. The deformation behavior will be examined by comparison of the post-tested microstructures in the base metals, heat-effected zone, and the fusion zones. We will also discuss the role of different phases on the weld/solidification behavior by compare those two model alloys.

4:20 PM  
Radiation-induced Segregation in Ni-based Concentrated Solid Solution Alloys: Mo-Rigen He1; Shuai Wang1; Shi Shi1; Ke Jin2; Hongbin Bei2; Kazuhiro Yasuda3; Syo Matsumura3; Kenji Higashida3; Ian Robertson1; 1University of Wisconsin-Madison; 2Oak Ridge National Laboratory; 3Kyushu University
    Single-phase concentrated solid solution alloys provide a fundamentally new avenue to enhance radiation damage tolerance by the increase of compositional complexity. However, less has been understood about the evolution of local chemical state in these materials as induced by irradiation. Here we present the defect microstructure and compositional profile in a series of Ni-based concentrated solid solution alloys (NiFe, NiCoCr, NiCoFeCr, and NiCoFeCrPd) under 1250 kV electron irradiation (at 400 °C, up to 1 dpa). All defects are interstitial-type, either Frank loops or perfect loops. Ni/Co segregates, while Fe/Cr (for all materials but NiFeCoCrPd) or Pd depletes at the loop plane. Moreover, the irradiated matrix of NiCoFeCrPd shows a three-dimensional modulated microstructure coupled with a decomposition between Ni/Co and Pd along <001> directions. These effects will be associated with the modification of energy dissipation processes and defect formation and migration energies, and contribute to the enhancement of radiation damage tolerance.

4:40 PM  
Development of High Entropy Alloy Foam with Ultra-low Thermal Conductivity and High Strength: Kook Noh Yoon1; Je In Lee1; Eun Soo Park1; 1Research Institute of Advanced Materials, Department of Materials Science and Engineering, Seoul National University
    Recently, high entropy alloys (HEAs) have received lots of attention as a new metallic material due to their superior properties including relatively high strength and low thermal conductivity. Furthermore, metallic foams generally exhibit low thermal conductivity due to their air-filled pores. Thus, it is possible to understand that HEA foams may show ultra-low thermal conductivity by cocktail effect of each material, while maintaining the promising properties of HEAs such as high strength and so on. In the present study, we first report HEA foam which is fabricated by dealloying process, selective dissolution, through galvanic coupling in phase separating FeCoCrNi-Cu HEAs. In particular, we will systematically assess property correlation between thermal conductivity and yield strength depending on the porosity. Indeed, we develop novel HEA foam with ultra-low thermal conductivity and high strength, which might be successfully applied as a heat shield material in harsh environment.

5:00 PM  
On the Influence of Crystal Orientation and Testing Temperature on the Local Mechanical Properties of High Entropy Alloys: Verena Maier-Kiener1; Benjamin Schuh2; Helmut Clemens1; Anton Hohenwarter2; 1Montanuniversität Leoben - Physical Metallurgy & Materials Testing; 2Montanuniversität Leoben - Materials Physics
    Recently, it has been shown for different High Entropy Alloys that these might show some microstructural instabilities during annealing resulting in a multi-phase structure, which occurs especially rapid in the nanocrystalline conditions and after prolonged times in the coarse-grained states. To gain more insights into the corresponding mechanical properties of differently annealed samples, nanoindentation was used and revealed drastic changes in hardness, and strain-rate sensitivity but also in the Young’s modulus. Besides a strong increase in the Young’s Modulus due to precipitation formation in the nc-conditions by annealing, a significant scatter in the coarsen-grained states was also found. Further tests in single crystalline but also single phase regions showed additionally a strong elastic anisotropy. Experiments were performed at room temperature and additionally at elevated temperatures up to 400°C in order to further investigate the thermally activated deformation components as well.

5:20 PM  Invited
Pre-osteoblastic Cell Responses to High-entropy Alloys: Jinbo Dou1; Haoyan Diao1; Yunzhu Shi1; Peter K. Liaw1; Shanfeng Wang1; 1University of Tennessee
    High-entropy alloys (HEAs) have advantages as potential bone-tissue-engineering materials. Here the AlxCoCrFeNi (x = 0.3, 0.5, and 0.7) HEAs were used as substrates to examine the effects of composition, surface roughness, grain size, and surface phase on the in vitro mouse pre-osteoblastic MC3T3-E1 cell attachment and proliferation, in comparison with Ti as the positive control. Al0.3CoCrFeNi was prepared by hot-isostatic processing, while the other two HEAs and Ti were prepared in the as-cast condition. The rough surfaces were polished to 600-grit surface finish, while the smooth surfaces were 1,200-grit surface finish. Different Al compositions in AlxCoCrFeNi HEAs resulted in different pre-osteoblastic cellular responses. Al0.5CoCrFeNi better supported MC3T3-E1 cell attachment and proliferation, showing the promise as a potential biomaterial for orthopaedic applications. Rough surfaces had scratches that could align MC3T3-E1 cells while smooth ones did not. The different grain sizes resulted from the processing methods also affected the MC3T3-E1 cellular behavior.