Advances in Multi-Principal Elements Alloys X: Structures and Modeling: Modeling and Characterization
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; Jennifer Carter, Case Western Reserve University; Srivatsan Tirumalai; Xie Xie, FCA US LLC; Gongyao Wang, Alcoa Technical Center
Thursday 2:00 PM
March 3, 2022
Room: 251B
Location: Anaheim Convention Center
Session Chair: Seungha Shin, University of Tennessee; Dustin Allen Gilbert, University of Tennessee
2:00 PM
High Thermal Stability B2 Precipitates in a Ru-containing Multi-principal Element Alloy: Carolina Frey1; Ravit Silverstein1; Tresa Pollock1; 1University of California Santa Barbara
Refractory Multi-principal Element Alloys (RMPEAs) present an opportunity for new high temperature alloys that can operate above 1200°C, but mechanical properties are currently limited by the lack of strengthening precipitates that are stable at high temperatures. Two phase microstructures composed of coherent B2 and BCC phases in (Al, Ti, Zr)-containing RMPEAs demonstrate high compressive strengths to 1000ºC but the B2 phase is not stable beyond 1200ºC. This presentation will discuss an equiatomic HfNbTaRuZr RMPEA synthesized by arc melting and annealed in a vacuum furnace between 1300 and 1575ºC. BCC, B2, and HCP phases in annealed materials were identified by both x-ray diffraction and transmission electron microscopy, with all phases stable up to 1575ºC. Refinement of the microstructure was achieved by splat quenching. Hardness measurements are reported for as-cast and splat quenched materials and compared to literature values. CALPHAD predictions are evaluated and implications for high temperature strengthening will be discussed.
2:20 PM
Effects of Short-range Order on Thermodynamic Properties of AlxCoCrFeNi High-entropy Alloys: Md Abdullah Al Hasan1; Seungha Shin1; Peter Liaw1; Dustin Gilbert1; 1University of Tennessee
Short-range order (SRO) in high-entropy alloys (HEA) have been observed both computationally and experimentally in recent research, and it was found that the SRO has a significant effect on the physical properties of the HEAs. However, no comprehensive work on the analysis of SRO and tuning of the properties of HEA has been performed. Also, it is very difficult to analyze the SRO and physical properties of many HEAs experimentally within a short time. In this work, the SRO parameter in the AlCrCoFeNi HEA structure and its corresponding thermodynamic properties were investigated using molecular dynamics (MD) simulations and density functional theory (DFT) calculations. Moreover, modern data analytics, such as correlation analysis and machine learning, were utilized to identify correlations among these properties and SRO parameters and predict thermodynamic properties for the HEA design.
2:40 PM
Local Configuration Effects on Vibrational Properties of BCC MPEAs: Sarah O'Brien1; Matthew Beck1; 1University of Kentucky
The role of entropy in reducing the free energy of formation of single-phase multi-principle element alloys (MPEAs) has been extensively discussed, particularly in terms of the role that configurational entropy plays in stabilizing solid solution phases. Recent studies, though, have highlighted the importance of vibrational entropy (Svib) and phonon densities of states (pDOS) in both MPEA thermodynamics and thermal conductivity. Vibrational properties of MPEAs are strongly affected by local configurations of constituent elements as these configurations control locally variable effective lattice strains and interatomic interactions. Taking solid solutions of refractory BCC elements (Mo, Ta, Nb, and W) with and without V as prototype MPEA systems, we have used density functional theory to explore the connections between specific local atomic arrangements and both pDOS and Svib. These results highlight the relative impact (on vibrational properties) and stability of specific local arrangements or clusters of atoms in prototype BCC MPEAs.
3:00 PM
Melting Temperature Prediction of Multi-principal Elements Alloys Using Ab-initio Calculations: Saswat Mishra1; Alejandro Strachan1; 1Purdue University
Many multi-principal elements alloys (MPEAs) have excellent high-temperature mechanical properties. Knowledge of the melting temperature of these alloys is critical from both applied and basic science points of view. Unfortunately, the experimental determination of the melting temperature of MPEAs is challenging. Thus, we use density functional theory-based molecular dynamics simulations to calculate the melting point of a representative MPEA alloy: equiatomic NbMoTaW. We obtain the free energy of the liquid and solid phases from their velocity power spectrum using the two-phase thermodynamic (2PT) framework to calculate the entropy. We quantify various sources of uncertainties in this approach by comparing its predictions with large-scale solid-liquid coexistence simulations. We find that the 2PT method tends to underestimate the melting temperature by up to 200K. Our results indicate that the melting temperature of NbMoTaW is 3250±200K and the method can be extended to characterize the melting temperature of various MPEAs.
3:20 PM
A Method to Predict Fluctuations in the Fault Energy Landscape of FCC Solid Solutions: Ritesh Jagatramka1; Chu Wang1; Matthew Daly1; 1University of Illinois at Chicago
Recent work suggests that the local chemical ordering of concentrated face-centered cubic (FCC) solid solutions introduces atomic-scale perturbations to the features of the generalized planar fault energy (GPFE) landscape. Within the context of deformation, these local perturbations introduce low-energy pathways for the evolution of deformation mechanisms (e.g., deformation twinning), which are of general interest to the metallurgy community. While the measurement of local fault energies has been reported in previous computational works, a framework to quantify their magnitude has yet to emerge. Here, we present a statistical method to predict the fluctuations in the GPFE of FCC solid solutions, taking only the overall alloy chemistry as inputs, and validate this framework using atomistic simulations. We anticipate that the analytical tools developed herein can be leveraged to design concentrated solid solutions with a prescribed, heterogeneous GPFE landscape.
3:40 PM Break
4:00 PM
The Impact of Short-range Order on Atomic Diffusions in Multi-principal Elements Alloys: Bin Xing1; William Bowman1; Penghui Cao2; 1Department of Materials Science and Engineering, University of California, Irvine; 2Department of Mechanical and Aerospace Engineering, University of California, Irvine
Vacancy diffusion is an essential process that has direct impacts on mechanical behaviors of materials such as creep. Here we studied the role of chemical short-range orders in vacancy diffusions in two classes of multi-principal elements alloys, including fcc CoCrNi and refractory MoNbTa through atomistic simulations. Our results show that, in the presence of chemical short-range orders, vacancy diffusions considerably slow down and the corresponding trajectories are more localized. Additionally, transition state calculations reveal that vacancy diffusion energy barriers are modified and enhanced to different degrees, depending on the associated element identity and its degree of ordering. The results indicate that controlling short-range orders can be an effective approach for manipulating vacancy kinetics and ion diffusivity.
4:20 PM
Vacancy Defects: Formation Energy and Migration Paths in Multi-principal-element Alloys (MPEAs): Ankit Roy1; Prashant Singh2; Ganesh Balasubramanian1; Duane Johnson2; 1Lehigh University; 2Ames Laboratory
Refectory-based multi-principal-element alloys (MPEAs) continue to garner great interest due to their remarkable mechanical properties, temperature stability, and higher radiation resistance. Here, using density-functional theory methods, we investigate point-defect energies and migration barriers in (Mo0.95W0.05)0.85Ta0.10(TiZr)0.05 to detail the effects of local chemical environments. Our findings suggest that the degree of lattice distortion in a disordered alloy is proportional to the charge transfer with the nearest neighbors. Stronger charge fluctuations for certain alloying elements were found to increase their migration barriers. Amongst all metals in the alloy, Ti was found to have the lowest migration barrier. However, the low Ti content suggests that the overall deformation due to Ti migration will be insignificant, resulting in negligible material degradation. This deformation resistance is anticipated to impart excellent radiation resistance to this MPEA.