HEA 2023: Characterization of HEAs I
Program Organizers: Andrew Detor, DARPA/DSO; Amy Clarke, Los Alamos National Laboratory
Monday 9:00 AM
November 13, 2023
Room: William Penn Ballroom
Location: Omni William Penn
Session Chair: Keith Knipling, Naval Research Laboratory
9:00 AM Introductory Comments
9:05 AM Invited
Short Range Order and the Evolution of Deformation Mechanisms in the CrCoNi Medium Entropy Alloy: Andrew Minor1; 1University of California-Berkeley
This talk will describe our recent results utilizing electron microscopy and nanomechanical testing techniques to provide insight into multiscale deformation phenomena in the CrCoNi medium entropy alloy. In order to understand the effect of Short Range Order (SRO) in terms of the evolution of plasticity at different stages, the technique of 4D-STEM was used during in situ deformation and fracture experiments. 4D-STEM can provide both real-space imaging and diffraction analysis during in situ testing, making it possible to perform strain mapping via diffraction pattern analysis during in-situ deformation in a TEM. Our results from electron microscopy are then correlated with mechanical testing including nanoindentation to examine how SRO evolves with different processing conditions. Lastly, we will consider the role of both SRO and planar defects in the both the mechanical response as well as structural determination via electron diffraction as a function of heat treatment in the CrCoNi MEA.
9:35 AM
Understanding Processing Pathways for Chemical Short-range Order in Equiatomic CoCrNi Alloy: Sakshi Bajpai1; Yuan Tian1; Yutong Bi1; Xin Wang1; Calvin Belcher1; Vivek Verma1; Benjamin MacDonald1; Timothy Rupert1; Xiaoqing Pan1; Enrique Lavernia1; Diran Apelian1; 1University Of California Irvine
The experimental detection of chemical short-range ordering (CSRO) in complex concentrated alloys (CCAs) has proven to be a difficult task. While predictions of CSRO have been well demonstrated by state-of-the-art modeling and simulation studies, there is a lack of conclusive experimental evidence regarding the evolution of CSRO in CCAs and its impact on mechanical behavior. This work systematically investigates the processing pathways that may induce CSRO in the ternary CoCrNi alloy by varying thermal treatment temperature, time, and cooling rates and characterizing the resulting microstructure. Appreciable variations in mechanical properties are established as a function of processing. Contributions to these properties are quantified with respect to various microstructural features measured through SEM EBSD as well as advanced TEM techniques. Critical considerations for the effective processing of CCAs are proposed and discussed.
9:55 AM
Towards More Robust EXAFS Analysis for Quantifying Short Range Order in Multicomponent Alloys: Brian DeCost1; Bruce Ravel1; Tyrel McQueen2; Mitra Taheri2; Howie Joress1; 1National Institute of Standards and Technology; 2Johns Hopkins University
Recent research has found that chemical short range order in high entropy alloys (HEAs) can play an important role on properties such as mechanical strength and corrosion resistance. EXAFS is a promising measurement technique for quantifying this aspect of local alloy structure and chemistry; however, the complexity of the models required for realistic analysis of multicomponent HEA systems poses a substantial barrier to obtaining meaningful insight. We present a principled Bayesian data analysis approach to EXAFS analysis to improve its reliability. We also show a novel approach to incorporate physical constraints into EXAFS models, with a focusing on the relationships between the short range order parameters for the different species in solid solutions. Our long term goal is automated online analysis that can drive adaptive measurement selection with the aim of enabling comprehensive understanding of the relationship between composition and short range order.
10:15 AM
Multi-scale Characterization of 3D Printable CrCoNi-based ODS-MPEAs by Advanced Stereo-STEM Cross-correlated with EDS: Milan Heczko1; Timothy Smith2; Christopher Kantzos2; Veronika Mazanova1; Antonin Dlouhy3; Michael Mills1; 1Ohio State University; 2NASA Glenn Research Center; 3Institute of Physics of Materials CAS
Our recent work (Nature, 2023) has demonstrated a new strategy to design alloys for high-temperature applications using additive manufacturing. Combining multi-principal element alloy (MPEA) and oxide-dispersion-strengthening (ODS) concepts opens up a vast unexplored compositional space to develop new 3D printable alloys. Here, we reveal the microstructural origins of the extraordinary performance of these new alloys using advanced multi-scale characterization approaches based on stereo-scanning transmission electron microscopy (STEM) cross-correlated with probe-corrected energy-dispersive X-ray spectroscopy (EDS). Stereo-STEM provides a direct and realistic 3D impression of the microstructure in a STEM foil. It enables precise measurement of local foil thickness, allowing quantitative assessment of the oxide dispersion including volume density and mean particle spacing. Combined with local defect density measurements, this approach provides detailed information about the microstructure of ODS-MPEAs. Critical aspects determining performance of 3D printable ODS-MPEAs are systematically identified and discussed.
10:35 AM Break
10:55 AM
Unraveling SRO in CrCoNi and FeCrCoNi Alloys: Insights from Indirect Methods: Francisco Coury1; Vinicius Bacurau1; Angelo Andreoli1; Eric Mazzer1; Robert Field2; Michael Kaufman2; 1Universidade Federal de São Carlos; 2Colorado School of Mines
This talk will discuss the challenges of characterizing short-range order (SRO) in Multi-Principal Element Alloys (MPEAs), especially in face-centered cubic (FCC) alloys. A series of results using direct and indirect methods for characterizing SRO in CrCoNi and FeCrCoNi will be presented and compared. The indirect methods include those that measure anomalies in functional properties. The direct methods involve the use of transmission electron microscopy methods including selected area diffraction pattern analysis to assess SRO. A framework will be proposed for establishing correlations between additional intensities and the presence of SRO in MPEAs. Our goal is to provide a better understanding of the ordering tendencies in multi-principal element alloys and highlight the potential of indirect techniques to these ordering tendencies.
11:15 AM
Diffuse Electron Scattering Reveals Kinetic Frustration as Origin of Order in CoCrNi Medium Entropy Alloy: Annie Barnett1; Dan Foley1; Mitra Taheri1; Michael Falk1; 1Johns Hopkins University
Equimolar CoCrNi is driven towards a long-range structure with transformation characteristics similar to that of a strain glass alloy due to the specific stoichiometry and applied aging conditions. This work illustrates the frustrated and kinetically arrested state of this alloy, which develops nano-size, single-phase, isostructural ordered domains at temperatures above 1273K within a matrix of solid solution. Upon aging at lower temperatures, both atomistic simulation and TEM investigation demonstrate the chemical sensitivity of the matrix by localized symmetry changes which suppress any long-range transformation, mirroring the kinetics observed in strain-glass alloys. Careful quantification of experimental and simulated diffraction patterns from various aging conditions reveal the degree of order in CoCrNi to increase given longer aging times, with achievement of longer domain length scales only when subjected to temperatures below 873K. This evidence indicates a kinetically constrained, chemically sensitive transition from a disordered fcc to a partially ordered, lower symmetry structure given adequate aging time and temperature. Magnetic effects on the transformation are dictated on the specific alloy stoichiometry and aging temperature, which act to amplify any effects of the glassy kinetics.
11:35 AM
Hard Zones and Superior Mechanical Properties Produced by Dense Nanoscale Recrystallization Twins in a Single-phase Heterostructured High-entropy Alloy: Shu-Yi Tung1; Ting-En Hsu1; Yuntian Zhu2; Ming-Hung Tsai1; 1National Chung Hsing University; 2City University of Hong Kong
Heterostructured high-entropy alloys (HSHEAs) integrate two innovative concepts in metallic materials that encompass alloy design and microstructural engineering. HSHEAs have demonstrated outstanding mechanical properties. However, the exploration of these materials remains challenging due to the intricate nature of their composition and microstructure. In this study, we introduced a heterostructure into a single-phase FCC HEA through cold rolling and partial recrystallization. This process resulted in an exceptionally high density of nanoscale recrystallization twins, leading to significant hardening and the formation of heterogeneous hard zones within the recrystallized regions. This tri-modal heterostructure induces secondary hetero-deformation-induced hardening, which sustains larger stable tensile plasticity, i.e. higher ductility. As a result, the alloy exhibits enhanced strength and ductility, yielding superior mechanical properties. The identification of the recrystallized hard zones is crucial for gaining a proper understanding of the hetero-zones in HEAs and provides valuable insights for the future design of HSHEAs.
11:55 AM
On the Strain Gradient Plasticity Phenomenon in CrCoNi Medium Entropy Alloys: Mobin Vandadi1; Tabiri Asumadu1; Desmond Klenam1; Nima Rahbar1; Winston Soboyejo1; 1Worcester Polytechnic Institute
This paper presents results of experimental and theoretical/computational study of the strain gradient plasticity phenomenon in CrCoNi medium entropy alloy (MEA). The size dependence of the mechanical properties of the as-cast, hot-rolled and heat-treated alloys were studied using the mechanistic and phenomenological theories. Numerical simulations were validated based on the experimental data across the various microstructural length scale. The hardness of the material changed as the processing methods varied. The statistically stored and geometrically necessary dislocations densities were high in the heat-treated samples than for the as-rolled and as- received conditions. The impact of processing parameters on material length and dislocation microstructure evolution are further elucidated. The underlying strain gradient plasticity mechanisms are elucidated before exploring the implications of the current results for the design of robust of low-cost medium entropy alloys structural applications.