High Entropy Materials: Concentrated Solid Solution, Intermetallics, Ceramics, Functional Materials and Beyond: Processing and Properties
Sponsored by: ACerS Basic Science Division, TMS Alloy Phases Committee
Program Organizers: Xingbo Liu, West Virginia University; Michael Gao, National Energy Technology Laboratory; Peter Liaw, University of Tennessee; Jian Luo, University of California, San Diego; Yiquan Wu, Alfred University; Yu Zhong, Worcester Polytechnic Institute
Wednesday 2:00 PM
November 4, 2020
Room: Virtual Meeting Room 33
Location: MS&T Virtual
Session Chair: Rajarshi Banerjee, University of North Texas; Kenta Yamanaka, Tohoku University
2:00 PM Invited
Highly Tunable Mechanical and Magnetic Properties in an Al0.3CoFeNi Complex Concentrated Alloy: Sriswaroop Dasari; Varun Chaudhary1; Bharat Gwalani2; Abhinav Jagetia2; Vishal Soni2; Stephane Gorsse3; Raju Ramanujan1; Rajarshi Banerjee2; 1Nanyang Technological University, Singapore; 2University of North Texas; 3University of Bordeaux, France
This talk will focus on the microstructure-mechanical-magnetic property relationships in an Al0.3CoFeNi high entropy alloy (HEA) or complex concentrated alloy (CCA). A novel nano-lamellar (FCC+L12) / (BCC+B2) microstructure was discovered in this alloy, exhibiting a tensile yield strength of 1074 MPa with a reasonable ductility of 8%. The same alloy can be tuned to form a more damage-tolerant FCC+B2 microstructure, retaining high tensile yield stress (~900 MPa) with appreciable tensile ductility (>20%), via annealing at 700°C. The FCC+B2 microstructure exhibits soft magnetic properties with saturation magnetization (Ms) of ~127 emu/g and coercivity (Hc) of ~151 A/m. The semi-hard nano-lamellar microstructure exhibits Ms ~138 emu/g and high Hc ~12732 A/m. This corresponds to more than eighty times increase in Hc and double the hardness in the same alloy. These results demonstrate the feasibility of producing a range of mechanical and magnetic properties by thermo-mechanical treatment of a single CCA composition.
2:20 PM
Corrosion Resistant Property Improvement of CoCrFeNiMoTi-based High Entropy Alloy by Optimizing Composition: Tatsuya Kimura1; Hiroshi Shiratori1; Kazuya Shinagawa1; Kosuke Kuwabara2; Yuzo Daigo2; 1HITACHI; 2Hitachi Metals
CoCrFeNiMoTi-based high entropy alloy (HEA) fabricated by selective laser melting (SLM) method has high strength and excellent corrosion resistant properties. In this study, the effect of each constituent element on the corrosion behavior was investigated for casted alloy. The results showed that Mo and Cr improved the corrosion resistant property, while Ni and Ti deteriorated it. From these results, the optimized composition of the alloy was proposed and SLM products of the proposed alloy were obtained using pre-alloyed powder. Although the pitting potential of the SLM product of the previously reported alloy was 0.82V vs. Ag/AgCl under 3.5% saltwater environment at 80°C, no pitting corrosion was observed in the SLM product of the alloy with the optimized composition under the same environment. It was confirmed that the corrosion resistant property was actually improved by the composition optimization.
2:40 PM Invited
Effect of Interstitial Nitrogen on the Phase Stability, Strengthening, Mechanical Behavior in TRIP-assisted High-entropy Alloys: Kenta Yamanaka1; Manami Mori2; Yusuke Onuki3; Shigeo Sato3; Akihiko Chiba1; 1Tohoku University; 2National Institute of Technology, Sendai College; 3Ibaraki University
High-entropy alloys (HEAs) showing transformation-induced plasticity (TRIP) have a great potential as a novel class of alloys with excellent mechanical properties. However, the yield strength of sole solid solution in such alloys is still low from the viewpoint of industrial applications. Here, we examined the effect of interstitial nitrogen on the mechanical behavior of a TRIP-assisted CoCrFeMnNi-based HEA. The results indicated that adding trace nitrogen (0.08 mass%) remarkably improved the stability of the matrix phase against low-temperature phase decomposition. Furthermore, an enhanced yield strength was achieved via the nitrogen addition with maintaining good ductility. Notably, thanks to the interaction between dislocations and nitrogen atoms, the metastable fcc phase of the N-doped HEA was effectively strengthened by introducing dislocations via hot deformation at the fcc stable temperatures. The TRIP behavior and dislocation dynamics in the studied alloys under tensile loading were examined by in-situ neutron diffraction measurements.
3:00 PM
Effect of Milling Parameters on Microstructure and Mechanical Properties of Mechanically Alloyed, Refractory High Entropy Alloy: Joshua Smeltzer1; Christopher Marvel1; B. Hornbuckle2; Anit Giri2; Kristopher Darling2; Martin Harmer1; 1Lehigh University; 2U.S. Army Research Laboratory
Mechanical alloying is an effective method to synthesize high strength, nano-structured HEAs. However, contamination is still an obstacle as it is difficult to predict properties based purely on thermodynamic considerations. Herein, four derivatives of a refractory MoNbTaW HEA, which is predicted as a single phase, were synthesized by altering milling media (tool steel and WC) and cryogenic liquid (N2 and Ar) to elucidate the effect of milling parameters on phase formation and mechanical properties. Light element contamination was measured using combustion gas techniques and microstructures of annealed alloys were characterized using aberration-corrected scanning transmission electron microscopy. Initial results show impurity concentrations vary up to 1 at.% under different milling conditions, thereby stabilizing distinct, multi-phase microstructures, and producing hardnesses that range 5 GPa. Overall, it is critical to understand and potentially control the effect of milling parameters (i.e. contamination) towards microstructural evolution and mechanical behavior of mechanically alloyed HEAs.
3:20 PM Invited
Thermal Stability of Refractory High Entropy Alloys at Intermediate Temperatures: Ke Jin1; Nannan Jia1; Yunfei Xue1; 1Beijing Institute of Technology
The structural stability of high entropy alloys can be compromised at intermediate temperatures, where the contribution of entropy is weakened but atomic migration remains active. In order to examine the metastability of refractory high entropy alloys in this temperature regime and shed light on the controlling factors, a series of equiatomic alloys with elements of Nb, Ti, V, Ta, Zr, and Hf are fabricated, which all exhibit a single-phase body-centered-cubic structure at homogenized states. Their phase stabilities are investigated during annealing for up to seven days at 400-700 ºC. Only a small portion of the alloys maintain stable, while majority of them, including all tested quinary alloys, experience decomposition and phase separation. The main features of structural evolution and elemental redistribution are understood by combining first-principles calculations and thermodynamic models. Formation enthalpy, especially lattice distortion energy, plays a critical role, while the impact of mixing entropy is not significant.
3:40 PM
ζ-Factor Microanalysis, a Quantitative Chemical Analysis Technique for the Characterization of High Entropy Alloys: Christopher Marvel1; Joshua Smeltzer1; Anit Giri2; B. Hornbuckle2; Kristopher Darling2; Martin Harmer1; 1Lehigh University; 2U.S. Army Research Lab
Mechanical alloying is an effective method to synthesize nanostructured HEAs that exhibit impressive properties. One caveat, however, is that metallic glass is often formed during high-energy synthesis and it is difficult to confidently predict which phases will form after re-crystallization. Inevitable introduction of light element impurities during the milling process is another practical complication for phase prediction. In an effort to develop quantitative techniques to best identify phases in nanostructured HEAs, this talk will introduce and demonstrate that ζ-factor microanalysis, a transmission electron microscopy (TEM) energy dispersive spectroscopy (EDS) framework, is a powerful tool to correlate microstructure to properties, especially when used in tandem with aberration-corrected atomic-resolution imaging. Here, a nanostructured mechanically alloyed refractory HEA was studied, which contained a variety of unpredictable yet important impurity phases regarding microhardness. Overall, ζ-factor microanalysis enabled full phase identification which would otherwise have been difficult due to severe X-ray absorption.