Phase Transformations and Microstructural Evolution: Non-Ferrous Alloys II
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Ashley Paz y Puente, University of Cincinnati; Mark Aindow, University of Connecticut; Sriswaroop Dasari, Idaho National Laboratory; Ramasis Goswami, Naval Research Laboratory; Megumi Kawasaki, Oregon State University; Eric Lass, University of Tennessee-Knoxville; Joshua Mueller, Michigan Technological University; Eric Payton, University of Cincinnati; Le Zhou, Marquette University
Wednesday 2:00 PM
March 22, 2023
Room: 25C
Location: SDCC
Session Chair: Swiswaroop Dasari, University of North Texas
2:00 PM Invited
Nucleation of Coupled Body-centered-cubic and Closed-packed Structures in Liquid Ni-Cr Alloys: A Molecular Dynamics Study: Deep Choudhuri1; 1New Mexico Institute of Mining and Technology
In the last four decades, the structure of pre-critical solid nuclei within a liquid phase of single-component face-centered-cubic (FCC) materials has been extensively investigated. These studies demonstrated that formation of equilibrium-FCC is mediated by metastable-body-centered-cubic (BCC) structured pre-critical nucleus. However, it is unknown if such nucleation mechanism is applicable to multi-component structural alloys that forms FCC and BCC structures as equilibrium phases. We have investigated this matter using Ni-35at.\%Cr and Ni-50at.\%Cr binary alloys via molecular-dynamics simulations. Our results indicated that the pre-critical and critical nucleus comprised coupled Cr-rich BCC and Ni-rich closed-packed (FCC and hexagonal-closed-packed) structures. Formation of such multi-structured pre-critical nucleus was facilitated by prior phase-separation of alloy-melt into Cr-rich and Ni-rich liquid-pockets. BCC and closed-packed regions inside the nucleus formed with non-equilibrium compositions that evolved over time. Thus, a non-conventional nucleation mechanism in concentrated Ni-Cr alloys allows them to solidify into FCC-BCC microstructures.
2:30 PM
Analysis of Self-healing Behavior in Co-based Superalloys by Spontaneous Segregation of Y during In-situ Tensile Test at Elevated Temperature: Hyun Gi Min1; Kook Noh Yoon1; Jung Soo Lee2; Eun Soo Park1; 1Seoul National University; 2Industrial Science and Technology Research Institute, Inha University
Since autogenous damage-healing enables to increase in the material life-cycle, self-healing metals have recently attracted significant attention. Especially, Self-healing is widely studied for high-temperature applications since most of it is obtained via diffusion of specific “healing agents.” In this study, we assessed the Y-addition effect of self-healing behavior in Co-based superalloys. The healing agent, Y, was carefully selected considering segregation tendency, strengthening effect, electronegativity, atomic size mismatch, etc., with Co. To assess the self-healing property of the Y-added superalloys, we conducted the in-situ tensile test at elevated temperatures in SEM. Firstly, we quantified the damage by measuring the KAM at different strains. At the same time, we analyzed the spontaneous segregation of Y to the damaged part, and the damage relief depending on Y segregation. Moreover, we confirmed that nano/micro-cracks could be closed by precipitating. This work is anticipated to provide a guideline for self-healing property development for high-temperature applications.
2:50 PM Invited
Nanoscale Shuffle Transformation in a Multifunctional Ti-Nb-Zr-Ta Alloy: Dian Li1; Deepak Pillai1; Yufeng Zheng1; 1University of Nevada-Reno
Shuffle transformation is a distinct class of displacive transformation, accomplished by the rearrangement of atom positions within the unit cell, with little or no pure strain of the lattice. In titanium alloys, body-centered cubic (bcc) beta phase to hexagonal omega phase transformation is a prototype shuffle transformation, in which every two of three adjacent {111} planes shuffle towards to the intermediate plane of the two leaving the third plane unaltered. In this work, we report another nanoscale shuffle transformation in a multifunctional Ti-Nb-Zr-Ta alloy, the bcc beta phase to orthorhombic O’ phase transformation. The structure of O’ phase was directly characterized using diffraction contrast TEM and z-contrast aberration-corrected S/TEM. The orthorhombic structure is generated by the shuffle of every other {110} planes of bcc lattice along the <1-10> directions. This work is supported by the National Science Foundation, grant DMR-2145844.
3:20 PM Break
3:40 PM
Combinatorial Design of Nano-scale Precipitate Strengthened High Entropy Alloy Exhibiting Transformation Induced Plasticity: Pradeep Konda Gokuldoss1; 1Indian Institute of Technology Madras
FeMnCoCr based high entropy alloys (HEA) are one of the prominent, metastable, multi-component systems that exhibit the unique behavior of transformation induced plasticity (TRIP). The emergence of HCP phase leading to martensitic microstructure during deformation from the metastable parent FCC solid solution phase provides the much-required phase-interface strengthening without compromising the ductility. However, to further improve the mechanical properties of these metastable alloys especially the yield strength, the TRIP effect alone appears to be not sufficient. Hence, this presentation will focus on the experimental design aspects including combinatorial synthesis of compositionally tailored alloys that can exhibit unique microstructures with concomitant precipitation strengthening in FeMnCoCr based HEA system. The crucial challenge of inducing nanoscale precipitate phases that are chemically homogenous in the metastable, FCC structured, low-stacking fault energy solid solution matrix without disturbing its unique behavior of TRIP will be discussed.
4:00 PM
Thermodynamic Study of Hf Addition to Refractory Low-activation W-Ta-Cr-V High Entropy Alloy from First-principles: Enrique Martinez Saez1; Andrew Alvarado1; Hi Vo Tin2; Jan Wrobel3; Damian Sobieraj3; Duc Nguyen-Manh4; Saryu Jindal Fensin2; Osman El-Atwani2; 1Clemson University; 2Los Alamos National Laboratory; 3Warsaw University of Technology; 4CCFE
Traditional material design methods become limited in the scope of high-entropy alloys (HEAs). HEA development requires an extensive survey of the compositional space across several principal elements. Combined computational methodologies are now available to efficiently examine the wide compositional space of alloys containing multiple principal elements. The union of Density Functional Theory (DFT) and the Cluster Expansion (CE) method produces a configuration-based energy expression to be probed and allows for an investigation of a large subset of systems for optimal and desired thermodynamic properties. We present a DFT-based CE model to predict the configurational energy of a multicomponent W-Ta-Cr-V-Hf quinary alloy. Coupled with Monte Carlo simulations we show that the model reproduces experimental observations. We analyze the thermodynamic properties of the W.31Ta.34Cr.05V.27Hf.03 system and observe two phase transitions, one order-disorder transition at 1250 K from fully random to separation and a second one at 620 K from separation to ordering.
4:20 PM Invited
Light-induced Microstructure Evolution in Inorganic Semiconductors: Dislocation vs. Deformation Twinning: Qi An1; 1Iowa State University
Photomechanical effects have been known for decades, while the underlying mechanism remains not fully understood. Here, we employed constrained density functional theory (cDFT) simulations to investigate how the light-induced e-h pairs affect the deformation and failure mechanisms in several typical semiconductors: ZnS, CdTe, and GaP. We found that ZnS exhibits ductile failure behavior under the ground state due to the dislocation dominated deformation mechanism. While deformation mode transforms to a twin dominated deformation mode when the electron-hole pairs are created, leading to a brittle failure. For covalent CdTe and GaP, we found that deformation mechanism remains dislocation dominated with the electron-hole pairs. In addition, the energy barriers for deformation slip are significantly reduced by high-concentration electron-hole pairs (∼10^21cm^−3), exhibiting metal-like ductility. Our results provide the theoretical basis to investigate the Photomechanical behaviors of semiconductors.
4:50 PM
Effect of β-stabilizer Elements on the α-β Interfacial Structure and Energies Using First-principles Calculations: Maheshwari Meesa1; Michael Baskes1; Rajarshi Banerjee1; Srinivasan Srivilliputhur1; 1University of North Texas
Titanium alloys, especially dual phase (α+β) alloys, such as Ti6Al4V, exhibit an excellent balance of mechanical properties and hence are commonly used as structural materials. During thermo-mechanical processing the α-phase forms from the parent high temperature β phase, with the α-β interfaces exhibiting the Burgers Orientation Relationship (OR). The defect-structure, energetics, and the role of β stabilizers(e.g V, Nb) on these interfaces are difficult to determine solely from experiments. Hence, first principles calculations have been used to study these interfaces assuming a random distribution of the β stabilizers. But in reality, the equilibrium concentration of the β stabilizers vary in the α and β phases. This work investigates the effect of concentration and distribution of the β stabilizing elements among the α and β phases and the interface on the interfacial energy and structure of the system using a Monte Carlo method using energies derived from first principles calculations.