High Entropy Alloys IX: Structures and Modeling : Structures and Characterization III
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
March 18, 2021
Room: RM 9
Location: TMS2021 Virtual

Session Chair: Keith Knipling, US Naval Research Laboratory; Jonathan Poplawsky, Oak Ridge National Laboratory

8:30 AM
Analysis of Multi-hit Events in Atom Probe Tomography of Refractory High Entropy Alloys: Patrick Callahan¹; Keith Knipling¹; ¹US Naval Research Laboratory
    Unlike traditional alloys, high entropy alloys (HEAs) are composed of multiple principal elements. This significantly expands the composition space and achievable properties of novel alloy systems. Despite a number of potential advantages of HEAs, there are still fundamental questions that need to be addressed, such as the mechanisms of dislocation motion and of diffusion in these alloys. Atom probe tomography (APT) enables the accurate determination of composition and morphology of microstructural features from ~250×250×1000 nm³ volumes from targeted regions of samples, enabling the study of phenomena such as atomic clustering, short range order, and anti-clustering, which are not well understood in HEAs. In this study, we will present an analysis of multi-hit detection events in the refractory HEAs MoNbTi and HfNbTaTiZr, and in turn the consequences on quantitative measurements in atom probe tomography.

8:50 AM  Invited
Heavy Ion Irradiation Response of AlxFeCrNiMn High Entropy Alloys: Nan Li¹; Di Chen²; Youxing Chen³; Jordan Weaver⁴; Yongqiang Wang¹; Saryu Fensin¹; Stuart Maloy¹; Amit Misra⁵; ¹Los Alamos National Laboratory; ²University of Houston; ³University of North Carolina; ⁴National Institute of Standards and Technology; ⁵University of Michigan
    In recent years, high entropy alloys (HEAs), composed of four or more metallic elements mixed in equal or near equal atomic percent, have attracted significant attention due to their excellent mechanical properties and good radiation resistance. They show significant promise as candidates for high temperature fission and fusion structural applications. Here, 5 MeV Fe2+ ion irradiation at 500 °C to a peak fluence of 50 and 100 displacement per atom (dpa) has been performed on single phase CrFeMnNi and dual-phase AlCrFeMnNi HEAs. Transmission electron microscopy with energy dispersive x-ray spectrometry was applied to characterize the radiation defects and microstructural changes. At the same irradiation condition, AlCrFeMnNi presented a higher density of voids but marginal radiation-induced hardening, in comparison to the single-phase CrFeMnNi. It is found in AlCrFeMnNi, chemical intermixing at the coherent FeCrMn matrix/AlNi precipitate interface is only observed when the radiation fluence reaches >or= 100 dpa.

9:15 AM  Invited
Understanding Radiation Resistance in High Entropy Alloys Through Atom Probe Tomography: Jonathan Poplawsky¹; Xing Wang¹; Wei-Ying Chen²; Tengfei Yang³; William Weber¹; Yanwen Zhang¹; ¹Oak Ridge National Laboratory; ²Argonne National Laboratory; ³Hunan University
    High-entropy alloys (HEAs) have become increasingly popular in the nuclear materials field because of their potentially superior radiation resistance compared to conventional alloys. Quantifying segregation in and around defect sinks is important for understanding elemental diffusion mechanisms as well as elemental mobility in radiation environments. Atom probe tomography (APT) is a unique technique capable of detecting segregation in and around defects in 3D with sub-nm resolution. A few HEA systems containing a range of 2-5 elements that were subject to ion irradiation will be presented to show segregation trends around defects and how these trends reveal why certain alloys are more radiation resistant than others. The information within the APT datasets can be used to better predict material properties for future alloy development. APT was conducted at ORNL's CNMS, which is a U.S. DOE Office of Science User Facility.

9:40 AM
Grain-scale Plastic Response of Equiatomic CoCrFeMnNi High-entropy Alloy Using High Energy Diffraction Microscopy: Jerard Gordon¹; Rachel Lim¹; Tony Rollett¹; Darren Pagan²; ¹Carnegie Mellon University; ²Cornell High Energy Sychrotron Source
    High-entropy alloys (HEAs) greatly expand the design space for structural materials by enabling almost unlimited compositional tuning. In particular, Cantor-based CoCrFeMnNi alloys and their derivatives have been shown to possess high strength and ductility values exceeding certain stainless steels. However, three-dimensional microstructure-to-property relationships for Cantor-based HEAs are not well understood and preclude significant advances in employing these materials in engineering design. Synchrotron-based High Energy Diffraction Microscopy (HEDM) was used to spatially map lattice orientation and the grain-average elastic strain tensor evolution of a equiatomic high-entropy alloy during in-situ deformation. Interrupted far-field (ff) HEDM scans were taken throughout deformation to capture the elastic regime, elastic-plastic transition, and subsequent plastic flow behavior up to 1% macroscopic strain. Furthermore, interrupted ff-HEDM scans were also performed during cyclic loading experiments at 0.3% and 0.5% strain in order to determine the evolution orientation gradients and Type II residual stress with cycling.

10:00 AM
Characteristics of Dislocation Slip in Refractory Multi-principal Element Alloys: Fulin Wang¹; Jean-Charles Stinville¹; Marie-Agathe Charpagne¹; Glenn Balbus¹; Leah Mills¹; Tresa Pollock¹; Daniel Gianola¹; ¹University Of California, Santa Barbara
    Refractory multi-principal element alloys (MPEAs) are promising for high temperature structural applications, yet their processing and deployment are limited due to poor ductility. We present our findings in two representative alloys, to elucidate the unique aspects of dislocation slip in BCC MPEAs that might contribute to desirable strength and ductility. The intrinsic dislocation behavior was investigated in single crystal environment in a strong alloy MoNbTi, by characterizing the dislocation dynamics during in situ tensile straining. The polycrystal plasticity, including the onset of slip and early plastic localization, was examined in a ductile alloy HfNbTaTiZr, using high-resolution digital image correlation (HR-DIC) analysis. The meso-scale investigation was complemented by transmission electron microscopy, especially at places of wavy slip, to determine in 3-dimensions the dislocation morphology. Together, our results lead to quantitative and statistical measurements of the slip resistance on different slip planes, that are linked to the unique properties of some MPEAs.

10:20 AM
Nitrogen-induced Solid Solution Hardening of an Austenitic (CrFeMnNi) HEA: Mathieu Traversier¹; Pierre Rinn¹; Emmanuel Rigal²; Anna Fraczkiewicz¹; ¹École des mines de Saint-Étienne; ²CEA LITEN
    Nitrogen is known as a strong austenite stabiliser in classical stainless steels, leading also to an efficient solid solution hardening. In this work, the effects of N on behavior of a non-equiatomic CrFeMnNi HEA have been studied. Four alloys (300g ingots) have been prepared by cold crucible melting and doped by nitrogen (up to 0.3 mass. %) in liquid state. Microstructure and phase stability were investigated through SEM/EDX and compared with thermodynamics predictions (Thermocalc). Mechanical characteristics have been evaluated from hardness measurements. Strong solid solution hardening effect of nitrogen has been shown, with an increase of hardness of 140 HV / mass % of N, accompagned by a significant increase of lattice parameter (0.3646 Å / mass % ). These values are similar or slightly higher of those measured in classical stainless steels.