HEA 2023: Oxygen Effects and Atomic-scale Processes
Program Organizers: Andrew Detor, DARPA/DSO; Amy Clarke, Los Alamos National Laboratory
Tuesday 9:00 AM
November 14, 2023
Room: Three Rivers
Location: Omni William Penn
Session Chair: Michael Miller, Southwest Research Institute
9:00 AM Introductory Comments
9:05 AM Invited
Metastability, Coarsening, and Strengthening Induced by Oxygen Interstitials in BCC Ti-Nb Alloys: Ravit Silverstein1; Florent Mignerot1; Nicoló Maria della Ventura1; Carlos G. Levi1; Tresa M. Pollock1; Daniel S. Gianola1; 1University of California, Santa Barbara
The design of refractory BCC alloys with interstitial elements, particularly those based on group number IV, reveals a unique combination of mechanical properties. Interstitial incorporation leads to phase instabilities in the BCC parent structure, resulting in a rich variety of new structures and microstructures. Compositional variance, coarsening behavior, and their corresponding effects on mechanical properties are actively being studied, but key mechanisms are not fully understood. The presence of Ti and Nb in most refractory multi-principal element alloys (RMPEs) makes their binary system attractive for establishing a fundamental understanding of the more complex RMPEs. This work elucidates the role of oxygen, in dilute concentration (~1 at%), in mediating phase evolution and transformation pathways in Ti-Nb alloys. Small-scale mechanical testing that can target specific O-mediated microstructures reveals exceptional properties with hardnesses and tensile yield strengths as high as 7 GPa and 3 GPa, respectively. Potential deformation mechanisms will be discussed.
9:35 AM
Oxygen-induced Hierarchical Heterogeneities and Enhanced Hardness in RMPEAs: David Beaudry1; Michael Waters2; Gianna Valentino3; Daniel Foley1; Nathan Smith2; Elaf Anber1; Yevgeny Rakita4; Charlie Brandenburg5; Jean-Philippe Couzinie6; Loic Perriere6; Toshihiro Aoki7; Keith Knipling8; Patrick Callahan8; Benjamin Redemann1; Tyrel McQueen1; Elizabeth Opila5; Christopher Wolverton2; James Rondinelli2; Mitra Taheri1; 1Johns Hopkins University; 2Northwestern University; 3University of Maryland; 4Ben Gurion University of the Negev; 5University of Virginia; 6University Paris Est Creteil; 7University of California, Irvine; 8U.S. Naval Research Laboratory
Refractory multiprincipal element alloys (RMPEAs) offer superiority to incumbent high-temperature structural alloys due to high melting points and retained strength at elevated temperatures. Of this class of alloys, those containing Group IV and V elements possess adequate ductility, low density, and the necessary formability. However, these elements have dramatically different interactions with oxygen, which creates uncertainty in predicting oxide evolution and in alloy design for oxidation resistance. We used high fidelity characterization and Monte Carlo simulations to decipher the complex sub-surface phase evolution during high-temperature oxidation of Group IV-V RMPEAs. We found that a refined hierarchical microstructure of phase-separated oxides form, which leads to a hardness increase of over 600% while preserving the ductility of the base metal. High-throughput computational screening identified doping elements that would capitalize on our fundamental phase evolution findings to improve oxidation resistance and mechanical properties in these alloys.
9:55 AM
Cracking the Code: Demystifying Early-stage Oxidation in High Entropy Alloys: Bharat Gwalani1; Andrew Martin1; Elizabeth Kautz1; Sten Lambeets2; Thevuthasan Suntharampillai2; Anil Battu2; Martin Thuo1; Matthew Olszta2; Sten Lambeets; Arun Devaraj2; 1North Carolina State Universtiy; 2Pacific Northwest National Laboratory
Oxide film formation on material surfaces, upon oxygen contact, is critical. While it can protect from further corrosion in some instances, it can also degrade the material over time. Therefore, it's vital to understand early oxide film formation stages for designing corrosion-resistant materials. This study utilized correlative and in situ techniques, specifically transmission electron microscopy (TEM) and atom probe tomography (APT), to examine oxide film's initial formation stages on a high entropy alloy (HEA). By observing the chemical changes and phase transformation from a single to a multi-layer oxide film over time, we garnered valuable insights into the process. This research underscores these techniques' potential in facilitating a deeper comprehension of oxide film formation, aiding in designing durable, corrosion-resistant materials.
10:15 AM
Combinatorial Exploration of Passivating Elements on Refractory High Entropy Alloys: Sebastian Lech1; Elaf Anber1; David Beaudry1; Howie Joress2; Charlie Brandenburg3; Brian DeCost2; Elizabeth Opila3; Mitra Taheri1; 1Johns Hopkins University; 2National Institute of Standards and Technology; 3University of Virginia
Refractory high entropy alloys (RHEAs) are candidate materials for next-generation high-temperature materials surpassing superalloys. However, despite high melting temperatures and promising mechanical properties, their oxidation resistance remains a challenge, limiting their applicability in extreme environments. Systematic exploration of passivating elements role is the key to unlocking the full potential of RHEAs. Current work explores experimental design strategies to enhance the oxidation resistance of RHEAs. The focus is on the addition of passivating elements and the development of compositional gradients using additive manufacturing via the directed energy deposition technique. The role of passivating elements on oxide scale formation was investigated by high-resolution scanning- and transmission electron microscopy along with phase analysis and thermodynamic modeling. Obtained results can be used as a guideline towards sufficient oxidation resistance of RHEAs for applications in aerospace and energy.
10:35 AM Break
10:55 AM
Microstructural Engineering in HEAs Undergoing Spinodal Assisted Phase Transformations: Shalini Roy Koneru1; Kamal Kadirvel2; Zachary Kloenne1; Hamish Fraser1; Yunzhi Wang1; 1Ohio State University; 2Computherm LLC
Researchers attributed the recently observed nano-scale periodic multi-phase microstructures in HEAs such as AlMo0.5NbTa0.5TiZr, Al0.5NbTa0.8Ti1.5V0.2Zr, TiZrNbTa and Fe15Co15Ni20Mn20Cu30 to spinodal assisted phase transformation pathways (PTPs). Microstructures in such HEAs could be further engineered by studying the underlying PTPs in detail and identifying the critical alloy and processing parameters affecting the microstructural evolution. Thus, through phase-field simulations, we investigated the effect of interplay between different alloy parameters such as volume fraction of, lattice misfit and modulus mismatch between coexisting phases on microstructure topology in HEAs undergoing spinodal assisted PTPs. We further systematically investigated the effect of different heat treatments such as isothermal aging vs continuous cooling vs two-step heat treatments on microstructural evolution. It is demonstrated that the microstructural topology could be inverted by appropriate selection of alloy composition and heat treatment design. Further, we illustrate that a range of hierarchical microstructures could be designed in HEAs undergoing spinodal assisted PTPs.
11:15 AM
B2 Phase in Refractory High Entropy Alloys: Macroscopic B2 Ordering Signal May Not Really Represent B2 Stability: An-Chen Fan1; Yun-Syuan Chen1; Chong-Chi Chi2; Chih-Hao Hsu1; Kai-Cheng Yang1; Daniel Miracle3; Ming-Yen Lu2; Ming-Hung Tsai1; 1National Chung Hsing University; 2National Tsing Hua University; 3AF Research Laboratory
Refractory high entropy alloys (RHEAs) with superalloy-like BCC+B2 microstructure, namely refractory high-entropy superalloys (RHESAs), have demonstrated superior resistance to thermal softening compared to single-phased BCC RHEAs, resulting in enhanced strength at elevated temperatures. However, the understanding of the equilibrium condition of the B2 phase in RHEAs remains unclear. In this study, three alloys from the Al-Nb-Ta-Ti-Zr system were selected to investigate the phase constituents, phase composition, and microstructure at different temperatures, as they potentially contain the B2 phase. Surprisingly, nanoscale interconnected structures consisting of BCC+B2 phases were observed in all the macroscopic "B2" phases in these alloys. Detailed analysis of these structures suggests that the B2 phases within the interconnected structure are formed through spinodal decomposition during the quenching process, indicating the absence of an equilibrium B2 phase above 700°C in the three alloys. The challenges associated with accurately identifying the equilibrium B2 phase in these materials are also discussed.
11:35 AM
Multi-principal Element Nanostructures via Nanosecond Laser-induced Dewetting: Ritesh Sachan1; Soumya Mandal1; Ashish Gupta1; Jordan Hachtel2; Andrea Konečná3; 1Oklahoma State University; 2Oak Ridge National Laboratory; 3Brno University of Technology
Multi-principal element alloy (MPEA) nanostructures have recently gained a great deal of attention due to their promising properties relevant to energy-relevant applications. However, the development of processing techniques that could fabricate MPEA nanoparticles with spatial order and tunable physical characteristics, such as size and microstructure, has been challenging owing to achieving a homogeneous mixing of constituent elements. Here we discuss how pulsed laser melting of ultrathin alloy films can be a powerful but simple and cost-effective technique to fabricate MPEA nanostructures. Ultrathin metal films (1-30 nm) on inert substrates such as SiO2 are generally unstable, with their free energy resembling that of a spinodal system. Such films can spontaneously evolve into predictable nanomorphologies with well-defined length scales. Here we review this laser-based experimental technique and provide examples of resulting robust nanostructures that can have applications in catalysis and optics.
11:55 AM
Synthesis & Characterization of Bulk Materials Towards the Development of Spinodally-hardened, Superhard High Entropy Ceramics: Christopher Desalle1; Caillin Ryan1; Ryan Crealese1; Simon Divilov2; Hagen Eckert2; Stefano Curtarolo2; Douglas Wolfe1; 1Penn State Applied Research Lab; 2Duke University
The increasing demand for materials that exhibit superior thermomechanical and thermochemical properties during extreme environment operation is driven by applications such as aerospace/hypersonic vehicles, friction stir welding, and machining. High entropy ceramic alloys have garnered significant interest due to a combination of solid-solution strengthening, phase stability control, and precipitation hardening effects via coherent spinodal decomposition. With a focus on the synthesis, analytical characterization, and performance evaluation of bulk materials, experimental advances have been achieved in relation to the development of spinodally-hardened, superhard high entropy ceramics. Attrition milling studies of various constituent ceramic nanoparticles for subsequent consolidation via field-assisted sintering technology (FAST) with in-situ heat treatments have enabled the synthesis of high entropy carbonitrides. This study highlights and deconvolutes the phase dependence of elasto-plasticity while introducing in-situ sintering heat treatments to realize the effects of spinodal nucleation and decomposition on phase evolution and mechanical properties.