Thermodynamics and Kinetics of Alloys: Session IV
Sponsored by: TMS Structural Materials Division, TMS: Alloy Phases Committee
Program Organizers: Ji-Cheng Zhao, University of Maryland; Wei Xiong, University of Pittsburgh; Chuan Zhang, CompuTherm LLC; Shuanglin Chen, CompuTherm LLC

Tuesday 2:30 PM
March 21, 2023
Room: Sapphire M
Location: Hilton

Session Chair: Chuan Zhang, CompuTherm, LLC; Giancarlo Trimarchi, Thermo-Calc Software AB


2:30 PM  Invited
Improvement of Co-Cr-Ni-Ta Mobility Descriptions: Kil-Won Moon1; Carelyn Campbell1; 1National Institute of Standards and Technology
    Interdiffusion data of five binaries and four ternaries were employed to improve the Co-Cr-Ni-Ta mobility descriptions. The current optimization method was the combination with a simulated annealing method and DICTRA calculations. The parameters were optimized based on the least square errors between the composition profiles of interdiffusion experiment data and calculated composition profiles by DICTRA. The advantage of this method is that multicomponent composition profiles can be employed to optimize without calculating diffusion coefficients. For quaternary system, all parameters except the ternary interaction parameters were cross-checked by at least two different alloy systems. When there was a discrepancy in the parameter, the selection was made by the parameter that had a smaller error after considering all related interdiffusion data at the same time. The challenges of implementing the optimized parameters into the database will be discussed.

2:50 PM  Invited
Calculation of Pourbaix Diagrams for Aqueous Corrosion: Kang Wang1; Bi-Cheng Zhou1; 1University of Virginia
    The Pourbaix diagram, or potential-pH diagram, is an electrochemical phase diagram which represents the thermodynamically predominant reaction products in aqueous corrosion. In this talk, two recent advances in the calculation of Pourbaix diagrams using the CALPHAD approach will be discussed for aqueous corrosion studies. First, a room temperature Pourbaix diagram considering oxide solid solutions, as a generalization of the traditional Pourbaix diagram with stoichiometric oxides, is constructed for an FCC single-phase high entropy alloy. By incorporating the solution models of complex oxides, this work presents a general and more accurate way to analyze the reaction products during aqueous corrosion of high entropy alloys. Second, a thermodynamic probability diagram is calculated to analyze the effects of Rb on the corrosion susceptibility of Cr-containing steels for nuclear materials canisters, which avoid the all-or-nothing approach to oxide formation typical of Pourbaix diagram. The formation of metastable species can be analyzed in aqueous environments.

3:10 PM  
Thermodynamics and Kinetics of Li-metal Alloys: Sesha Behara1; Anton Van der Ven1; 1University of California Santa Barbara
    In recent years, there has been a push towards using Li metal as anode materials in Li-ion batteries in order to extract more energy density. Li-metal anodes are generally unsafe due to the formation of dendrites that penetrate through the electrolyte, causing electrical shortage. To overcome this issue, there were some recent studies that proposed coating the anode with alloys of Li with various elements such as In, Bi, Zn, and As. These alloy coatings, while acting as a buffer layer, should facilitate fast diffusion of Li ions, and also be less prone to drastic phase transitions during charging/discharging. Using high throughput first principles calculations, in this work we explore various thermodynamic and kinetic properties of a wide range of Li-alloys that show promising behavior.

3:30 PM  
Prediction of the Microstructure and Corrosion Behavior for the CoyCryFeyMnyNix High-Entropy Alloys by the CALPHAD Method: Yu-Xuan Ho1; Sin-Yi Chen1; Yee-Wen Yen1; 1National Taiwan University of Science and Technology
    High-entropy alloys (HEAs) have excellent physical, chemical and mechanical properties, such as high strength and hardness, excellent corrosion resistance and thermal stability. For investigation the Ni addition effect into Co-Cr-Fe-Mn-Ni HEAs, the calculation of phase diagram (CALPHAD) method was applied to calculate the constituents of alloys, and the Pandat software with the PanHEA database was used for simulation. Seven CoCrFeMnNix (x= 0.21, 0.44, 0.7, 1.0, 1.33, 1.71 and 2.15 in molar ratio) alloys were prepared. The calculation and experiment results revealed that the seven alloys mainly composed of FCC phase. However, Alloy 1 (x= 0.21) had two phases after heat treatment. For the other alloys, the calculation results were mostly consistent with experimental results. For corrosion behavior test, alloy 5 (x= 1.33) has the lowest corrosion rate. Because Alloy 1 (x= 0.21) has the second phase that is Cr-rich phase, the highest hardness value was measure in Alloy 1.

3:50 PM Break

4:10 PM  
Calculation of Critical Points: Shuanglin Chen; Rainer Schmid-Fetzer1; John Morral2; 1Clausthal University of Technology; 2The Ohio State University
    Miscibility gaps appear in many alloy systems and so do spinodal and critical points. Three methods are presented for determining a critical point in a multicomponent system. The first method uses Gibbs thermodynamic conditions for spinodal and critical points. The second method for a critical point uses the fact that the third directional derivative of Gibbs energy along the eigenvector direction of Gibbs energy Hessian must be zero at a critical point. The third method uses the geometric features of binodal, spinodal, and eigenvector of Gibbs energy Hessian to determine the position of a critical point on a spinodal curve. The thermodynamic conditions for a spinodal and critical point in a binary system will be naturally extended to a multicomponent system in terms of directional derivatives of Gibbs energy.

4:30 PM  
Symbolic Regression Search for a General Free Energy Function for BCC Alloys: Luke Wirth1; Snigdhansu Chatterjee2; Alexander Urban3; Dallas Trinkle1; 1University of Illinois Urbana-Champaign; 2University of Minnesota; 3Columbia University
    Prediction of phase diagrams at new compositions enables discovery of novel materials for engineering applications. Identification of general thermodynamic functions for the free energies of crystal structures at finite temperatures would provide powerful tools for making these predictions. We search for such a function to describe BCC alloys based on physical features of their constituent elements. To prepare our model, we collect functions from thermodynamic database (TDB) files that calculate the free energy of the BCC phase, at given conditions, relative to stable reference phases at standard conditions for CALPHAD models. Data science tools, such as the sure independence screening and sparsifying operator (SISSO) compressed-sensing method, then connect coefficients that act on functions of temperature and composition to elemental features. The resultant models offer a physically meaningful way to make predictions about the stability of alloy phases in regions of composition space that have not been studied experimentally.

4:50 PM  
Interfacial Properties and Crystal Growth of Ni, Ti and Ni50Al50 from Molecular Dynamics Simulations: Roberto Rozas1; Pedro Toledo2; 1University of Bío Bío; 2University of Concepción
     Molecular dynamics simulations are used to study crystal growth and interfacial properties in metallic systems of Ni, Ti and Ni50Al50. This study is focussed on the simulation of crystal-liquid interfaces at the melting temperature Tm, i.e.~in equilibrium. From the analysis of capillary-wave fluctuations, the interfacial stiffness and free energy as well as kinetic growth coefficients for different crystal orientations are determined. Here, the growth coefficients are extracted from time- and wavenumber-dependent height-height correlation functions. The kinetic growth coefficients are also estimated using the free solidification method and compared to those obtained from the capillary-wave fluctuations. While the B2 crystalline structure of Ti (bcc) and Ni50Al50 (B2) lead to much smaller anisotropies of the interfacial properties than those of the face-centered cubic (fcc) crystalline structure of Ni, the crystal growth in pure systems as Ni and Ti is a factor of about 10 faster than that in the binary Ni50Al50 alloy.We acknowledge financial support by Centro CRHIAM Project ANID/FONDAP/15130015 and Project ANID/FONDECYT/1190101.