Grain Boundaries and Interfaces: Metastability, Disorder, and Non-Equilibrium Behavior: Alloying, Solute Segregation, and Precipitation: Part I
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Computational Materials Science and Engineering Committee, TMS: Chemistry and Physics of Materials Committee, TMS: Phase Transformations Committee
Program Organizers: Yue Fan, University of Michigan; Liang Qi, University of Michigan; Jeremy Mason, University of California, Davis; Garritt Tucker, Colorado School of Mines; Pascal Bellon, University of Illinois at Urbana-Champaign; Mitra Taheri, Johns Hopkins University; Eric Homer, Brigham Young University; Xiaofeng Qian, Texas A&M University
Tuesday 8:00 AM
March 1, 2022
Room: 304C
Location: Anaheim Convention Center
Session Chair: Yue Fan, University of Michigan, Ann Arbor; Liang Qi, University of Michigan, Ann Arbor; Garritt Tucker, Colorado School of Mines
8:00 AM Invited
Spectrum-based Isotherms for Grain Boundary Segregation: Christopher Schuh1; Malik Wagih1; Nutth Tuchinda1; Thomas Matson1; 1Massachusetts Institute of Technology
There are two complementary views of grain boundary segregation common in the literature: (i) thermodynamic isotherms, which treat an ‘average’ segregation response of many sites, and (ii) specific segregation-site-based analysis, which is often limited to symmetric boundaries. Thanks to advances in computing and data science, it is now possible to combine these methods into a spectral isotherm model that can treat complex systems including polycrystals. This talk will review our development of the spectral isotherm model, including its rigorous calculation for individual polycrystalline alloys and the use of data science to extend its reach to many systems. The development of a complete model requires many details, including a dilute-limit spectrum, a correction for solute interactions at higher concentrations, and the effects of triple junctions and grain size-dependence. Ultimately, the spectral approach solves many problems with classical models and permits rigorous thermodynamic assessment of nanocrystalline alloys.
8:30 AM
Atomic-scale Analysis of Heterogeneous Nickel Solute Segregation into Random Grain Boundaries and Polycrystals: Frederic Sansoz1; Eve-Audrey Picard1; Tara Nenninger1; 1The University of Vermont
Different segregation types in nanocrystalline alloys have been described in the literature as either homogeneous or heterogeneous, which differently impacts their mechanical properties. In heterogeneous segregation, solute atoms are clustered along some grain boundaries (GBs), while other GB regions remain solute-free, as evidenced with Ni segregation in nanocrystalline Ag. This talk presents our recent efforts to better understand solute atom arrangements within random GB networks, with particular focus on heterogeneous Ni segregation in different FCC, BCC and HCP alloys. Using hybrid MC/MD, we simulated and analyzed solute segregation in random Ag, Al, Nb and Zr polycrystals, each with same solute content of 4 at.% Ni. A spectrum of segregation configurations from fully heterogeneous to fully homogeneous is revealed. Second, a fast algorithm based on atomic-scale GB segregation energy spectra was developed and applied to quantify the alloy tendency for heterogeneous segregation in both symmetric GBs and random GBs of polycrystals.
8:50 AM
Competition Between Shear Coupling and Sliding in Doped Nickel Grain Boundaries: Spencer Thomas1; Jason Trelewicz1; 1Stony Brook University
The Disconnection Model, originally applied to explain shear-coupled grain boundary (GB) migration and GB sliding, has grown to a general description of GB migration and stress interactions, driving full-scale microstructure evolution models. Every GB has a set of disconnection modes, each with an associated step height and burgers vector. The nucleation/migration barriers of different modes determine GB mobility, shear-coupling, and sliding under general stress conditions. It is generally unknown how these barriers are influenced by dopants – this is critical, as alloying is necessary to stabilize nanocrystalline polycrystals. Dopants generally impede GB migration, but it is not known how dopants affect shear-coupling and sliding. We developed a method to determine barriers via molecular dynamics and statistical theory and show that the Σ39[111] symmetric-tilt GB shows greater sliding proclivity in a Ni-Cu alloy relative to pure Ni. This method can be automated and used to generate barrier databases and predictive models.
9:10 AM
Contributions of Triple Junctions and Quadruple Nodes to Grain-size Dependent Intergranular Segregation: Nutth Tuchinda1; Christopher Schuh1; 1Massachusetts Institute of Technology
Recent developments on the computation of the solute segregation spectrum provide the distributions of intergranular segregation energies relevant for nanocrystalline alloys. However, nanocrystalline materials contain a significant population of higher-order grain junctions (triple junctions and quadruple nodes) that can manifest in the total segregation spectrum, causing segregation to be grain size-dependent. Here, we employ a defect identifying algorithm to separate segregation spectra for grain boundary, triple junction and quadruple node sites in polycrystals. We found that in the range of 5-20 nm in grain size, the subspectra are effectively grain size-independent, but the total spectrum depends on the grain size due to their relative fraction in the intergranular network. These results are discussed in terms of thermodynamic contributions, providing a better understanding of nanocrystalline alloys at their finest grain sizes.
9:30 AM Break
9:45 AM
2nd Generation of Nanocrystalline Cu-3Ta with Improved Precipitate Coherency: Billy Hornbuckle1; Josh Smeltzer2; Albert Ostlind1; Blake Fullenwider1; Chris Marvel2; Anit Giri1; Martin Harmer2; Kiran Solanki3; Kris Darling1; 1US Army Research Laboratory; 2Lehigh University; 3Arizona State University
While a multitude of strategies to enhance a material’s strength exist, the creation and maintenance of coherent interfaces between precipitates and the matrix is one of the most effective and well established methods. Nanocrystalline Cu-Ta has utilized this strategy, in the form of coherent Ta-rich atomic clusters which exhibited spherical morphologies. These clusters form spontaneously and stochastically upon thermal decomposition, thereby providing an opportunity to interject additional engineering design through further solute additions. Subsequently, the authors have taken the next evolutionary step with the discovery and strategic formation of a novel ordered structure in chemically optimized, nanocrystalline Cu-3Ta alloy. The new cuboidal atomic clusters exhibit enhanced coherency and stability relative to their spherical predecessors imparting the alloy with improved physical response. Atom probe tomography and aberration-corrected STEM determined the cluster’s crystal structure and chemistry, and the role they played to prevent coarsening at elevated temperatures.
10:05 AM Invited
Influence of Contaminates on Nanocrystalline Thermomechanical Stability: Jonathan Priedeman1; B. Chad Hornbuckle2; Kristopher Darling3; Sean Fudger3; Gregory Thompson1; 1University of Alabama; 2Army Research Laboratory ; 3Army Research Laboratory
Nanocrystalline alloys have received considered interest owing to their high strength with reduced grain size. Upon thermal and/or mechanical loading, these nanocrystalline grains can coarsen with strategies to mitigate this growth achieved by the partitioning of specific solutes to the grain boundaries. In this work, we discuss how the solute selection and its interaction with impurities influences the mechanisms of stability and mechanical performance. We report this behavior using different Cu-based nanocrystalline alloys that have been fabricated by cryogenic ball milling and subsequent powder consolidation. The reactivity of the solute with the contaminate species found in the processed alloys creates specific clusters/precipitates and, in certain situations, the reactive product has a profound impact on the thermo-mechanical behavior.
10:35 AM
Corrosion-induced Grain Boundary Migration: Yang Yang1; Weiyue Zhou2; Sheng Yin3; Qin Yu3; Daniel Schreiber4; Jim Ciston3; Mark Asta3; Michael Short2; Andrew Minor3; 1The Pennsylvania State University; 2Massachusetts Institute of Technology; 3Lawrence Berkeley National Laboratory; 4Pacific Northwest National Laboratory
Engineering the grain boundaries (GBs) in materials can offer superior performance such as high strength and high ductility. However, GBs are dynamic and can be changed by external stimuli such as heating, mechanical deformation, or radiation damage. Recently, it has been shown that corrosion can also lead to the migration of GBs, and the resultant microstructural heterogeneity may impact the damage tolerance significantly. Here we show direct experimental evidence of GB migration in Ni-20Cr after corrosion in molten salt. Furthermore, the GB migration also led to the formation of a de-alloyed zone which was enriched in Ni and depleted in Cr. Combining advanced electron microscopy characterization and DFT modeling, we probed the excess vacancy concentration in the de-alloyed zone and identified it as the precursors of pores. Our results provide important insight into the GB stability under extreme conditions.
10:55 AM
Origins of Weak Strengthening Effect in As-cast Al-Si Alloys: Wenqian Wu1; Mingyu Gong1; Bingqiang Wei1; Amit Misra2; Jian Wang1; 1University of Nebraska-Lincoln; 2University of Michigan
Al-Si casting alloys are usually composed of α-Al and eutectic mixture of Al-Si with Si flakes. The Si and Al matrix generally hold cube-on-cube orientation relationship with the (111)Al||(111)Si interface. Several conventional strategies, such as modifying the geometry, size or distribution of Si flakes, are used to tailor mechanical properties of Al-Si casting alloys. However, the strengthening effect of Si flakes is very limited. Using molecular dynamics simulations, we revealed that the weak shear resistance of Al-Si interface, the low formation energy and migration energy of point defects in Al-Si interface can be origins of weak strengthening effect of Si flakes in Al-Si casting alloys. Our results show that the weak shear of the interface is due to easy glide of interface misfit dislocations, and weak strengthening effect is due to easy cross-slip and climb of lattice dislocations at interfaces.