Probing Defect Properties and Behavior under Mechanical Deformation and Extreme Conditions: Defect-mediated Mechanical Performance and Damage Tolerance
Sponsored by: TMS Nanomechanical Materials Behavior Committee, TMS Nuclear Materials Committee, TMS Mechanical Bahavior of Materials Committee
Program Organizers: Zhe Fan, Lamar University; Tianyi Chen, Oregon State University; Shijun Zhao, City University of Hong Kong; Mitra Taheri, Johns Hopkins University; Yury Osetskiy, Oak Ridge National Laboratory
Tuesday 2:00 PM
October 19, 2021
Room: B140/141
Location: Greater Columbus Convention Center
Session Chair: Jian Wang, University of Nebraska-Lincoln; Tianyi Chen, Oregon State University
2:00 PM Invited
Designing Metal and Amorphous Ceramic Composites for Extreme Conditions: Jian Wang1; Binqiang Wei1; 1University of Nebraska-Lincoln
Strong, ductile, and irradiation tolerant structural materials are in urgent demand for improving the safety and efficiency of advanced nuclear reactor. Amorphous ceramics could be very promising candidates for high radiation tolerance since they do not contain conventional crystal defects that are induced in crystalline materials under irradiation. However, amorphous ceramics exhibit ‘brittle-like’ behavior. We realized the strength-ductility-irradiation tolerance combination of amorphous ceramic composites (ACCs) through tailoring nanosized heterogeneities. Principles for the design of such ACCs are that metal elements should prefer to form nanosized metal-rich clusters in ACCs. Moreover, the phase structure and properties of the heterogeneity can be modified by synthesis and annealing conditions. By averting plastic flow localization and enhancing irradiation tolerance, we impart to ACCs the ability to undergo both uniform plastic deformation and irradiation tolerance, markedly advancing their potential for use in nuclear industry as core structural materials.
2:30 PM
Estimating the Strengthening Parameters for Irradiated Alloys Using Atomic Scale Dislocation Dynamics: Osetsky Yury1; 1Oak Ridge National Laboratory
Models based on the dispersed barrier hardening (DBH) approach are often used for interpreting experimental results and estimating the mechanical response of irradiated materials. However, weakly physically based approaches and phenomenological fitting to the experimental data do not allow accurate accounting for obstacle size and temperature effects. In this work, we developed a simple approach that combines early parametric continuum modeling with current atomic scale dislocation dynamics. This approach allows us to estimate size and temperature dependent values of obstacle strength parameters, using the available atomistic modeling data. Examples are presented for cases in two materials of practical significance. These are voids, helium bubbles, copper precipitates, and rigid obstacles (imitating oxide particles) in bcc iron and voids and rhenium-rich precipitates in tungsten. The implication of these results to the understanding of experimental observations is discussed.
2:50 PM
Investigating Deformation Mechanisms in Ni-based Superalloys with Compact γ'- γ" Coprecipitates: Semanti Mukhopadhyay1; Hariharan Sriram1; Richard DiDomizio2; Andrew Detor2; Robert Hayes3; Gopal B. Viswanathan1; Yunzhi Wang1; Michael Mills1; 1The Ohio State University; 2GE Global Research Center; 3Metals Technology Inc.
Compact coprecipitate morphology in IN718 based alloys, consisting of γ'' phase on all {100} faces of cuboidal γ' precipitates, has been shown to possess superior coarsening resistance. A microstructure consisting of such a coarsening resistant morphology of γ' and γ'' coprecipitates was stabilized in two IN718-variant alloys through careful control of alloy chemistry and processing parameters. Detailed mechanical characterization of these alloys and consequent deformation mechanisms operative in these novel IN718-based superalloys will be discussed. Results from in-situ high-temperature tensile tests and ex-situ high-resolution characterization of creep deformed microstructures (DC-STEM, HR-STEM) will be utilized to investigate the deformation behavior of the alloys across different length scales. The findings will be complemented with the microstructural characterization of creep deformed conventionally processed IN718. The experimental findings will be supplemented with results from a microscopic phase-field model.
3:10 PM
Nanomechanical Properties of Neutron Irradiated Austenitic Steels: Tianyi Chen1; Mack Cullison1; 1Oregon State University
Predicting and controlling the radiation-induced microstructure evolution and mechanical degradation in reactor structural materials are of primary importance for the sustainability of current nuclear power plants and the deployment of future nuclear energy forms. Advanced austenitic alloys are widely used as structural materials in LWRs and cladding materials in fast reactors. They are also candidate materials for the next-generation sodium-cooled fast reactors. Driven by the need for accelerated screening, qualification, and development of advanced nuclear materials, irradiation, post-irradiation characterization, and small-scale mechanical testing have been applied to the advanced austenitic alloys.The microstructural and chemical evolutions of different alloys after neutron radiation were characterized and compared. Radiation-induced defects and precipitates were quantified and used to rationalize the changes in nanomechanical properties. The deformation microstructure were further characterized to illustrate the roles of defects in modulating the deformation mechanisms of the alloys.
3:30 PM Break
3:50 PM
Local Phase Transformation Strengthening in Ni-based Superalloys: Ashton Egan1; Fei Xue2; Timothy Smith3; Longsheng Feng1; Shakthipriya Baskar1; Emmanuelle Marquis2; Yunzhi Wang1; Maryam Ghazisaeidi1; Michael Mills1; 1Ohio State University; 2University of Michigan; 3NASA Glenn Research Center
In the intermediate temperature creep regime of Ni-based superalloys (~700 °C) deformation is dominated by planar defects and microtwinning, where deformation response is controlled by segregation events surrounding the leading partial dislocations. Of particular interest are alloys exhibiting Local Phase Transformation (LPT) along planar defects, a dynamic process whereby the alloy can be strengthened during service. The propensity for LPT strengthening depends on the relative ratio of η and/or χ formers, depending on active mechanisms, and in this study the LPT composition regime was explored with several commercial and novel alloys. Advanced characterization of the deformation mechanisms and LPT was accomplished by Scanning Transmission Electron Microscopy (STEM), Energy Dispersive X-Ray Spectroscopy (EDS), Atom Probe Tomography (APT), and SEM-based Electron Channeling Contrast Imaging (ECCI), while being supported by density functional theory (DFT) and phase field computational techniques. Understanding these complex phenomena is crucial in creating a homogenized constitutive creep model.
4:10 PM
Phase-field Modeling of Electromigration-mediated Void Migration and Coalescence under Mechanical and Current-stressing in Interconnect Lines: William Farmer1; Sree Vemulapalli1; Kumar Ankit1; 1Arizona State University
Electromigration (EM) occurs due to a momentum transfer between the metallic ions of the interconnect and the electrons, which drift in the direction of the externally applied electric field. EM-induced defects can manifest as nucleation and growth of micro-voids and hillocks, grain boundary (GB) slits, and metallization, which lead to failure of interconnects and soldered joints. In order to gain an understanding of interconnect failure mechanisms, we use a phase-field model to simulate the morphological evolution of voids under different operating conditions. Our simulations display the effects of elastic inhomogeneity, high current densities, and applied and back-stress on the migration and coalescence of voids. Based on an in-depth parametric study, inferences are drawn to formulate strategies for which the void migration in interconnects can be suppressed.
4:30 PM
Mechanical and Microstructural Responses of Severe-plastic Deformed High Entropy Alloys under Irradiation: Spencer Doran1; Tracey Spoerer1; Megumi Kawasaki1; Youxing Chen2; Di Chen3; Tianyi Chen1; 1Oregon State University; 2University of North Carolina Charlotte; 3University of Huston
High Entropy Alloys (HEAs) have received increased attention due to their unique properties and resilience in harsh environments such as next generation nuclear reactors. High-pressure torsion (HPT) introduces nanograins in HEAs that may further enhance mechanical strength. The stability of the nanograins and their potential defect sink effects in severely deformed HEAs are not well known and the subject of this study. Equiatomic CoCrFeNiMn samples are severely deformed by HPT and then irradiated at 100 peak displacements per atom (DPA) at 500 °C with 3.4MeV nickel ions to a fluence of 1.0919×10^17 cm-2. Material properties of the CoCrFeNiMn HEA are investigated using nanoindentation, electron microscopes and the Surface Acoustic Wave (SAW) characterization techniques. This study aims to demonstrate the importance of grain size on defect evolution in HEAs in high radiation environments as well as how HPT-introduced mechanical properties and microstructures are changed by these environments.