Alloy Behavior and Design Across Length-Scales: An SMD Symposium Honoring Easo George: Alloy Design and Behavior
Sponsored by: TMS Structural Materials Division, TMS: High Temperature Alloys Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Michael Mills, Ohio State University; George Pharr, Texas A&M University; Robert Ritchie, University of California, Berkeley; Muralidharan Govindarajan, Oak Ridge National Laboratory
Tuesday 2:30 PM
March 21, 2023
Room: Cobalt 502B
Location: Hilton
Session Chair: Robert Ritchie, University of California, Berkeley
2:30 PM Invited
Functional High Entropy Alloys: Dierk Raabe1; Zhiming Li1; Liuliu Han1; Ziyuan Rao1; 1Max-Planck Institute
This presentation is about recent progress in the field of high-entropy alloys that have interesting functional properties, at maintained good mechanical properties, for which some of these materials are known. Five specific topics are illuminated, namely, high-entropy alloys with interesting soft magnetic, electrocatalytic, hydrogen tolerant, and wear resistant properties. Although these features are in part also available from other alloy systems, their combination with good mechanical properties makes them particularly attractive for future applications in fields related to sustainable energy conversion, electrification and corrosion resistance.
3:00 PM Invited
Utilizing Nanoprecipitates to Modulate Phase Transformation, Strength, and Ductility of HEAs: Ying Yang1; Eva Zarkadoula1; Easo George1; 1Oak Ridge National Laboratory
Solid solution high-entropy alloys (HEAs) with the face-centered cubic (fcc) structure can exhibit extensive tensile ductility and excellent toughness, but their room-temperature strength tends to be low. To increase strength, obstacles to dislocation motion such as precipitates are typically added. However, with few exceptions, they tend to embrittle the materials. Precipitates, in addition to spatially confining dislocations and increasing strength, can also retard phase transformation. In this presentation, we will demonstrate a strategy that utilizes computational thermodynamics and kinetics to control nanoprecipitate characteristics, thereby to independently tune both phenomena. The precipitates, by synergistically modulating the strength and transformation of the HEA matrix, produce alloys with improved strength and ductility. We will also discuss molecular dynamics simulation results to show how individual variables such as precipitate size, spacing, volume fraction, and/or the chemical driving force of matrix phase transformation can affect deformation mechanisms.
3:30 PM Invited
Fracture Properties of High-entropy Alloys: Bernd Gludovatz1; Robert Ritchie2; 1UNSW Sydney; 2Lawrence Berkeley National Laboratory
Since the concept of high-entropy alloys (HEAs) as materials with at least four or five principal elements in (near)-equiatomic composition was introduced in 2004, this new class of materials has penetrated essentially all materials science-related fields. The main reason for this is that some face-centered cubic alloy compositions have been shown to exhibit outstanding mechanical properties with extraordinary combinations of strength, ductility and fracture toughness, particularly at cryogenic temperatures, whereas certain body-centered cubic refractory compositions display outstanding high-temperature strength. While significant effort has been put into rapid screening and narrowing of the compositional space of HEAs to a manageable scope, there are still only a few metallic alloys have been discovered that push the limits of mechanical performance. Here we review work on some of the most damage-tolerant HEAs discovered to date and discuss the fundamental reasons why their resistance to fracture and subsequent stable crack growth is so exceptional.
4:00 PM Break
4:20 PM Invited
Factors Affecting Mechanical Twinning in Single-phase FCC and Polycrystalline MEAs and HEAs: Guillaume Laplanche1; 1Ruhr-University Bochum
In this study, recent progress will be presented in understanding the factors influencing the uniaxial stress above which mechanical twins are observed in medium- and high-entropy alloys (MEAs/HEAs) from the Cr-Mn-Fe-Co-Ni system. Efforts were made to produce alloys that are single-phase face-centered cubic (FCC), chemically homogeneous and have well-controlled grain sizes. Tensile tests at 293 and 77 K were interrupted at different strains and systematically characterized by transmission electron microscopy. The uniaxial twinning stress was found to be temperature independent and to increase with decreasing grain size. When the twinning stress is extrapolated to infinite grain size, it increases linearly with the intrinsic stacking fault energy. The results obtained in the present study will be compared to those of experimental and theoretical studies focusing on single crystals.
4:50 PM Invited
Predicting High Entropy Alloy Phase Stability across Length Scales: James Morris1; German Samolyuk2; Yury Osetsky2; G. Malcolm Stocks2; 1Ames Laboratory; 2Oak Ridge National Lab
One of the challenges for theory is to predict behaviors without prior information, providing both contact with experiments and the ability to predict behaviors not yet observed. In this talk, I will highlight theoretical work motivated directly by experimental efforts from Easo George. In particular, I will focus on phase stability of high entropy alloys and related materials. The prediction of specific behaviors of alloys requires a consideration of more than entropy. Understanding the role of enthalpy led to the ability to make reasonable predictions of which compositions are likely to form single-phase alloys. These concepts have been refined, and have proven to be reasonable through a great expansion of experimental results since originally formulated. We will also discuss how the disorder of 3- and 4-component alloys of 4f and 5f metals can stabilize a particular crystal structure, through non-entropic contributions. <BR>This work was supported by DOE’s BES-MSE program.
5:20 PM Invited
Low Temperature Deformation Mechanisms of CrMnFeCoNi High-entropy Alloy Polycrystals: Werner Skrotzki1; G. Dan Sathiaraj2; Rolf Schaarschuch1; Carl-Georg Oertel1; Paul Chekhonin3; Robert Chulist4; Christian Gadelmeier5; Uwe Glatzel5; Easo P George6; 1TU Dresden; 2IIT Indore; 3Helmholtz-Zentrum Dresden-Rossendorf; 4Polish Academy of Sciences, Krakow; 5University of Bayreuth; 6University of Tennessee
The polycrystalline CrMnFeCoNi high-entropy alloy was deformed in tension at temperatures between 4 K and 300 K. Stress – strain curves were taken until fracture. Thermal activation parameters were derived from stress relaxation tests. Moreover, the microstructure and texture development was studied. It is found that the deformation behavior changes characteristically at certain temperatures. This relates to yielding, serrated flow, work-hardening, fracture, microstructure and texture formation. The different deformation mechanisms operating at low temperatures in this advanced metal alloy will be demonstrated and discussed.