Deformation Induced Microstructural Modification: Session I: Deformation of Pure Metals and Model Alloys
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Shaping and Forming Committee
Program Organizers: Arun Devaraj, Pacific Northwest National Laboratory; Suveen Mathaudhu, Colorado School of Mines; Kester Clarke, Los Alamos National Laboratory; Bharat Gwalani, North Carolina State Universtiy; Daniel Coughlin, United States Steel Corp
Monday 8:30 AM
March 15, 2021
Room: RM 38
Location: TMS2021 Virtual
Session Chair: Arun Devaraj, Pacific Northwest National Laboratory
8:30 AM
Introductory Comments: Deformation Induced Microstructural Modification: Arun Devaraj1; 1Pacific Northwest National Laboratory
Introductory Comments
8:35 AM Invited
Phase Evolution in Two-phase Alloys during Severe Plastic Deformation: Nirab Pant1; Nisha Verma1; Yinon Ashkenazy1; Pascal Bellon1; Robert Averback1; 1University of Illinois at Urbana-Champaign
Phase evolution in FCC metals with strongly interacting alloy components during severe plastic deformation is investigated using molecular dynamics simulations. Specifically, we study the alloy microstructure in steady state, nucleation and growth of precipitates in supersaturated alloys, and the decomposition of precipitates in undersaturated alloys. The results are compared to a modified effective temperature model. Key observations are nucleation and growth of precipitates during SPD at a temperature of 100 K; Gibbs-Thomson-like behavior relating solubility to precipitate size under steady-state shearing; a direct relationship between the effective temperature and the shear modulus; and the importance of cluster agglomeration in precipitate growth. The study also reveals that the mechanisms of forced chemical mixing depends on precipitate size, adding complications to effective temperature models in inhomogeneous systems. The simulations are shown to provide good semiquantitative agreement with experimental findings reported in the literature.
9:05 AM
Extreme Shear-deformation-induced Modification of Defect Structures and Hierarchical Microstructure in Immiscible Alloy: Bharat Gwalani1; Matthew Olszta1; Anqi Yu2; Krassimir Bozhilov2; Soumya Varma3; Siddhartha Pathak3; Aashish Rohatgi1; Suveen Mathaudhu1; Peter Sushko1; Cynthia Powell1; Arun Devaraj1; 1Pacific Northwest National Laboratory; 2University of California, Riverside; 3Iowa State University
Extreme shear deformation is used for material processing methods and is unavoidable in many engineering applications in which two surfaces are in relative motion against each other while in physical contacts, such as in ball bearings. The mechanistic understanding of the microstructural-evolution of multi-phase metallic systems under extreme shear deformation is still in its infancy. Here, we highlight the influence of shear deformation on the microstructural hierarchy & mechanical properties of binary as-cast Al-xSi & Cu-xNb alloys. Shear-deformation-induced grain refinement, multiscale fragmentation, and metastable solute saturated phases with distinctive defect structures led to a two-fold increase in the flow stresses determined by micropillar compression testing. These results highlight that shear deformation during solid-phase processing can achieve non-equilibrium microstructures with enhanced mechanical properties in these immiscible alloys. The experimental insights obtained here are especially crucial for developing atomic-scale predictive models for microstructural evolution of metallic alloys under extreme shear deformation.
9:25 AM Invited
Microstructural Changes in Nanotwinned Metals under Various Deformation Modes: Andrea Hodge1; 1University of Southern California
Highly nanotwinned (nt) metals have shown a strength comparable to nanocrystalline metals, while maintaining other desired properties including ductility, conductivity, and thermal stability. However, the deformation mechanisms and mechanical stability of the nt metals is not yet fully understood but can be directly linked to large number of Sigma 3 boundaries. In this presentation, results from highly aligned nt samples tested in compression, torsion, and tension under various loading/testing conditions relative to the twin boundary (TB) direction will be presented. The microstructural evolution of the tested samples was analyzed before and after deformation for each loading configuration.Overall, the nt structure was observed to be mostly stable, in which, to a significant extent, the nanotwins survived without major changes in twin size, orientation, or twin density. However, distinct differences in the overall deformation of the samples and in the extent of the changes were observed.
9:55 AM
Effect of Cryogenic Equal Channel Angular Pressing on Mechanical Behavior and Microstructure of Pure Copper: Pedro Oliveira1; Danielle Magalhães1; Andrea Kliauga1; Vitor Sordi1; 1Federal University of São Carlos
The aim of the present work was to perform ECAP on pure copper at cryogenic temperature (193 K) and compare the effects on mechanical behavior and microstructure with the ECAP performed at room temperature (298 K). The ECAP procedure was performed using a die with an angle between the channels (Φ) of 120° and an outer curvature angle (Ψ) of 22°. The samples were processed at both temperatures, up to ten ECAP passes (10X), giving an equivalent strain of ~6.7. The billets processed at 193 K via ECAP achieved higher values of hardness, yield and ultimate tensile strength. This also indicated a combination of grain refinement, high dislocation density and energy stored in a form of microstructural defects, higher than those achieved at 298 K. Hence, it was concluded that cryogenic ECAP is an effective route for promoting grain refinement and, consequently, promote an increase in mechanical strength.
10:15 AM
Influence of Deformation on Microstructure of Al4Si and Cu4Nb Alloys during Friction Stir Processing: A Multi-modal Microstructural Characterization Study: Julian Escobar1; Bharat Gwalani1; Matthew Olszta1; Joshua Silverstein1; Luciano Bergmann2; Jorge dos Santos2; Peter Staron2; Emad Maawad2; Benjamin Klusemann2; Suveen Mathaudhu2; Arun Devaraj1; 1Pacific Northwest National Laboratory; 2Helmholtz-Zentrum Geesthacht
The mechanistic understanding of the influence of friction stir processing (FSP) on the microstructural modification of metallic alloys is still inadequate, due to the complex interplay of extreme strain and deformation induced heating. The microstructural changes from atomic to macroscale due to FSP can dramatically reduce grain size, increase the ductility to rupture and fatigue life of cast Al-Si and Cu4Nb alloys, making it crucial to decipher such deformation induced microstructural modification mechanisms. To achieve this goal, we used the FlexiStir friction stir and processing system to process Al4Si and Cu4Nb sheets, followed by detailed ex-situ synchrotron-based high-energy x-ray diffraction analysis, thermocalc predictions and electron microscopy. Our results provided new insights on the differences in lattice parameter and full-width-at-half-maximum of diffracted peaks, which could be correlated to the temperature and extent of shear deformation in the microstructure across base metal, heat affected zone, thermomechanically affected zone and stir zone.
10:30 AM Invited
Hierarchical Microstructure in Shear Bands of Pure Titanium: Xiaolong Ma1; Dexin Zhao2; Dinakar Sagapuram2; Kelvin Xie2; 1Pacific Northwest National Lab; 2Texas A&M University
A comprehensive understanding of the shear band microstructure is the key to control the ductility of materials. However, large localized deformation usually develops within this thin region, and nanoscale recrystallized grains are formed. Conventional characterization techniques such as EBSD and regular TEM imaging are inadequate to visualize the detailed microstructure inside these shear bands. For example, EBSD cannot provide high enough spatial resolution. TEM has the ability to determine the nanoscale grain size, but to elaborate the orientation of all grains is labor-intensive. Moreover, detailed orientation information cannot be obtained. In this work, we demonstrated that ASTAR (a technique that acquires the diffraction pattern of each pixel) could offer direct orientation information of microstructure feature down to 1nm scale. Using the ASTAR results, we revealed the hierarchical structure including high-angle grain boundaries, low-angle grain boundaries, defect bundles in the shear bands.