Phase Transformations and Microstructural Evolution: High Entropy Alloys
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Rongpei Shi, Harbin Institute of Technology; Yipeng Gao, Jilin University; Fadi Abdeljawad, Lehigh University; Bharat Gwalani, North Carolina State Universtiy; Qi An, Iowa State University; Eric Lass, University of Tennessee-Knoxville; Huajing Song, Los Alamos National Laboratory
Wednesday 2:00 PM
March 17, 2021
Room: RM 57
Location: TMS2021 Virtual
Session Chair: Bharat Gwalani, Pacific Northwest National Laboratory
2:00 PM
Microstructutal Evolution of Metals at High Temperature Revealed by In-situ Neutron and Synchrotron X-ray Diffraction: Klaus-Dieter Liss1; 1Guangdong Technion - Israel Institute of Technology (GTIIT)
In-situ neutron and synchrotron X-ray diffraction deliver unique insights into the microstructural evolution of metals under exotic conditions. Comprehensive exploitation of scattering signals include multi-dimensional reciprocal-space studies on a number of individual grains and local information. For each constituting phase, their statistics and temporal behavior reveal information about grain growth or refinement, subgrain formation, static and dynamic recovery and recrystallization, slip systems, and twinning. Those methods can reveal local information in heterogeneous materials, such as phase composition, lattice parameters, strain, texture, crystalline disorder etc. This presentation reviews examples on heat treatment of metals before and after severe plastic deformation, global and local texture, and mechanically induced phase transformation while future potential for such characterization and development is risen.
2:20 PM Cancelled
Atomistic Modeling of the Effects of Precipitates in Phase Stability of Fe-Ni Based Alloys: Eva Zarkadoula1; Ying Yang1; Albina Borisevic1; Easo George1; 1Oak Ridge National Laboratory
Ni-based superalloys exhibit exceptional mechanical properties, such as high-temperature strength and toughness, primarily due to the presence of stable L12-type precipitates. Recent experimental and computational studies have shown that stable L12 precipitates can be formed in Fe-Ni based alloys, which are considered a low-cost alternative to Ni-based alloys. Additionally, it has been shown that the precipitate size can significantly affect the strain-driven deformation of the matrix. In this work, molecular dynamics simulations were employed to investigate fundamentally the role of precipitates in deformation and phase transformation of Fe-Ni based alloys under shear stress. We investigate the interaction of dislocations with L12 precipitates, and the effects of the size of the precipitates and distance between them on phase stability in Fe-Ni based alloys.
2:40 PM
Microstructural Characterization of As-cast Al2.7CrFeMnV, Al2.7CrFeTiV, and Al2.7CrMnTiV High Entropy Alloys: Keith Knipling1; Patrick Callahan1; David Beaudry2; Richard Michi3; 1U.S. Naval Research Laboratory; 2Johns Hopkins University; 3Oak Ridge National Laboratory
Three high entropy alloys that have potential as lightweight structural materials have been studied using a combination of atom probe tomography (APT), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and X-ray diffraction (XRD) as well as predictions from Thermo-Calc. The first alloy, Al2.7CrFeMnV, is a single-phase bcc, consistent with Thermo-Calc predictions. The two other alloys contain multiple phases. The second alloy, Al2.7CrFeTiV, is a solid solution bcc matrix with an Al-rich G-phase and a Laves phase rich in Ti and Cr. These were all present in the Thermo-Calc predictions. The third alloy, Al2.7CrMnTiV, is also bcc with an L10 phase, which was predicted by Thermo-Calc. Additionally, a nanoscale B2 phase in the form of coherent ~10 nm B2 cuboids is formed, resembling the γ-γ' microstructure of Ni-based superalloys but in a bcc system.
3:00 PM
Comparison of Low Temperature Oxidation Behavior of Pure W and MoNbTaW Thin Films: Robert Quammen1; Paul F. Rottmann1; 1University of Kentucky
Multi-principal element alloys (MPEAs), also known as high entropy alloys (HEAs), have been widely researched since their initial development by Cantor, et al. Recently, refractory MPEAs have begun to garner more attention due to their exceptional high temperature mechanical properties. However, it is well known that the performance of refractory MPEAs at elevated temperatures is limited by oxidation. Improving the phase stability of MPEAs—both internally (i.e. suppressing intermetallic formation) and externally (i.e. oxidation)—is crucial to enabling their use in high temperature applications. In this work, the onset of oxidation in pure W and MoNbTaW is studied by leveraging multi-scale characterization techniques (e.g. SEM, TEM, XRD, nanoindentation, and in-situ micro-tensile testing) to observe microstructural and mechanical changes in sputtered films before and after low-temperature annealing in air. Through understanding of the initial stages of oxidation, the alloy chemistry can be tailored to improve phase stability in extreme environments.
3:20 PM
Hydrogen-induced Microstructural Transformations in an FeMnCoCr High-entropy Alloy: Maria Ronchi1; Haoxue Yan1; Shaolou Wei1; C. Tasan1; 1Massachusetts Institute of Technology
The microstructural effects of hydrogen (H) on high-strength alloys greatly complicate the problem of H embrittlement (HE). This challenge is especially relevant when it comes to iron-based alloys which can undergo multiple phase transformations and which exhibit transformation-induced plasticity. In this study, we investigate the impact of H on an Fe-Mn-based metastable high-entropy alloy (HEA) and the evolution of its microstructure. To this end, we employ a unique integrated scanning electron microscopy-thermal desorption spectroscopy technique. This enables us to use electron backscattering diffraction and electron channeling contrast imaging to monitor H influences on the austenite stability and HCP-martensite formation in this material, similar to that seen in stainless steels. Moreover, the introduction of H also leads to the formation of twins within the HCP-martensite. In this talk we reveal the underlying mechanisms of these transformations and explore how these insights can apply to the search for HE-resistant HEAs.
3:40 PM
Stacking Fault Energy in Metastable Alloys: Mulaine Shih1; Maryam Ghazisaeidi1; 1Ohio State University
In this work, we examine the stacking fault energy (SFE) in concentrated alloys to gain insight about the deformation mechanisms. The goal of this work is to understand the fundamental meaning of SFE in concentrated alloys, which not only have a range of SFE values, but also varies from positive to negative in recent computation predictions. We choose NiCo alloy as our model system to perform atomistic simulations. We study the concept of average versus “local” SFE and examine the distribution and the temperature-dependence of SFE. We also interrogate the dislocation behaviors in positive, zero and negative average SFE alloys, and analyze the force balance on the dislocations. The results explain the discrepancy between experimental measurements and computation predictions of SFE in medium and high entropy alloys.