Mechanical Response of Materials Investigated Through Novel In-Situ Experiments and Modeling: On-Demand Oral Presentations
Sponsored by: TMS Structural Materials Division, TMS Functional Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Thin Films and Interfaces Committee
Program Organizers: Saurabh Puri, Microstructure Engineering; Amit Pandey, Lockheed Martin Space; Dhriti Bhattacharyya, Australian Nuclear Science and Technology Organization; Dongchan Jang, Korea Advanced Institute of Science and Technology; Shailendra Joshi, University of Houston; Josh Kacher, Georgia Institute of Technology; Minh-Son Pham, Imperial College London; Jagannathan Rajagopalan, Arizona State University; Robert Wheeler, Microtesting Solutions LLC

Monday 8:00 AM
March 14, 2022
Room: Characterization
Location: On-Demand Room

Integrated Discrete Dislocation Plasticity Modelling, HR-EBSD and TEM Characterisation of Ti Dwell Fatigue: Yilun Xu1; Sudha Joseph1; Phani Karamchad1; David Dye1; Fionn Dunne1; 1Imperial College
     Dwell fatigue mechanisms in Ti alloy IMI834 have been investigated using discrete dislocation plasticity (DDP) modelling of a novel sample comprising neighbouring textured regions aligned well and badly respectively for slip to reflect micro-textured regions observed in components. New thermo-mechanical DDP capability [1] to model the sample microstructure under dwell fatigue loading has provided quantitative analysis of prism slip pile-ups at hard/soft grain boundaries, developing stresses high enough to activate basal slip in the neighbouring hard grain region. HR-EBSD has provided elastic strains and hence stresses at the experimentally characterised hard/soft interface. TEM analysis has provided quantitative detail of the dislocation slip activation and pile-ups at the interface [2]. Direct comparison of model results with both EBSD and TEM quantitative characterisation has justified a predictive modelling method for dwell fatigue lifetime. [1] Xu, Y, et al. Intl. Jnl. Plasticity.[2] Xu, Y, et al. Nature Comms.

Atomistic Insight into Cumulative Twin-solute Interactions in Mg Alloys: Yang Hu1; Vladyslav Turlo2; Dennis Kochmann1; 1ETH Zurich; 2Empa
    Magnesium (Mg) alloys are essential for numerous industrial applications but poorly understood from a mechanics perspective, while a comprehensive understanding of their mechanical behaviors can guarantee a more efficient alloy design as well as a greater application potential. Twinning, as one of the key deformation mechanisms in Mg and Mg alloys, is investigated in this work. We use atomistic simulations to perform systematic studies on the effect of nine alloying elements, different solute compositions, and applied stresses on twin embryo growth in Mg alloys. We demonstrate that Li, Y, and Nd promote twinning, while Al, Zn, Sn, Ca, Pb, and Ce have a negative effect. This effect is caused by the local interaction of solute atoms with interfacial dislocations/disconnections on various twin/matrix interfaces, which also controls the final 3D configuration of the twin embryo. Our results contribute important new insights needed for developing more efficient, more durable, stronger, lighter, and safer structural materials.

In-situ TEM Observation of Shear Induced Microstructure Evolution in Cu-Nb Alloy: Shuang Li1; Matthew Olszta1; Lei Li1; Bharat Gwalani1; Ayoub Soulami1; Cynthia Powell1; Suveen Mathaudhu1; Arun Devaraj1; Chongmin Wang1; 1Pacific Northwest National Laboratory
    Phase boundaries in multiphase alloys govern defect interaction and chemical intermixing across different phases during plastic deformation. Dynamic interaction of defects with phase boundaries in multiphase alloys, especially for immiscible alloys, has been topic of significant research interest in recent years. Here, we describe a novel approach for carrying out in-situ TEM shear deformation to directly observe interfacial microstructural evolution of a Cu-Nb alloy. A unique double shear specimen geometry is microfabricated by a FIB technique to apply shear deformation upon push loading inside the TEM. From the real-time observation, we discover that the phase boundary with a zigzag morphology effectively blocks stacking faults nucleated in a Cu grain from slipping into a Nb grain. Meanwhile, the Cu phase bears the most plastic deformation through slip or twinning mechanisms. This work sheds light on understanding the shear deformation and the behavior of phase boundaries in multiphase alloys during shear deformation.

Micro-mechanical Investigation of a High-pressure Torsion Processed Nano-crystalline WCu Composite: Michael Burtscher1; Markus Alfreider1; Klemens Schmuck1; Daniel Kiener1; 1Montanuniversitaet Leoben
    In this study, the micro-mechanical properties of a high-pressure torsion processed WCu alloy were determined. To this end, a coarse-grained WCu rod material was deformed at room temperature and 200°C with 0.5, 5 and 50 turns, respectively. In the following, the microstructure was illuminated by SEM and TEM imaging, and the grain size of the respective material was determined by a customized watershed algorithm. The phase composition was analyzed using XRD measurements, while micromechanical properties were investigated using in-situ cantilever experiments. This enabled to determine the fracture toughness and J-integral, where a strong influence of the microstructural conditions could be determined. This phenomenon is largely governed by the remaining coarse W grains within the nanocrystalline WCu matrix, as well as the mechanical alloying of Cu in W and vice versa. Hence, the current work enables to identify favourable deformation conditions for optimised fracture toughness of WCu alloys.

In-situ Digital Image Correlation Study to Reveal Cyclic Plastic Strain Localizations in Stainless Steel 316L: Elif Cansu Kursun1; Koenraad G.F. Janssens1; Philippe Spätig1; 1Paul Scherrer Institute
    Fatigue damage of polycrystalline metallic alloys involves localized plastic strains at a microstructural scale. To develop a mechanistic understanding of the damage accumulation, the evolution of micro-scale strain fields under cyclic loading needs to be characterized. Digital Image Correlation (DIC) can be used for quantitative analysis of local strain distributions at various length scales. When a suitable patterning technique allowing sufficient spatial resolution is chosen, DIC analysis can reveal sub-grain size deformation characteristics. In this work, in-situ DIC is used to characterize cyclic plastic behavior of a stainless steel 316L. A three dimensional-DIC approach is used for accurate quantification of micro-scale strain fields in in-situ testing conditions. The strain localizations within the grains under cyclic loading are linked with microstructural features of 316L investigated using Electron Backscattering Diffraction. The strain fields emerging in individual grains are analyzed as a function of the number of cycles.

Effect of Hole Shape and Pattern Orientation on Mechanical Behaviour of Two-dimensional Micro-lattice through In Situ Micro-tensile Testing: Dhriti Bhattacharyya1; Alan Xu1; Michael Saleh1; 1Australian Nuclear Science and Technology Organization
    The mechanical behaviour of two-dimensional micro-lattices fabricated from <100> oriented single crystal Ni samples was studied using in situ micromechanical testing device inside a scanning electron microscope. Three different samples were tested, two with regular hexagonal holes, and one with round holes, all samples having equal hole area fraction. The two sets of samples with hexagonal holes had the hexagons oriented at 0° and 30° with respect to the tensile axis, while the sample with round holes had the holes oriented at 0°. The tensile strength of the sample with hexagonal holes oriented at 0° was higher than the one oriented at 30°, and it had a considerably lower ductility. However, the sample with circular holes at 0° orientation had a tensile strength and ductility similar to that of the hexagonal 0° sample. Thus, it was seen that hole orientation was more important in determining the properties than hole shape.

Tensile and FatigueTesting of Metallic Thin Films with Ultra-thin Passivation Layers: Sunkun Choi1; Ho Jang Kim1; Yu Hyun Park1; Gi-Dong Sim1; 1KAIST
    For the design of reliable micro/nano-scale devices, it is essential to know the size-dependent properties of materials. Accordingly, researchers tried to investigate the intrinsic properties of thin films. However, in real applications, there are only few cases where films are placed as freestanding. Therefore, it is crucial to understand the performance of thin films with and without a passivation layer. In this work, we report on the changes in mechanical behavior of sub-micron metallic films by deposition of ultra-thin (< 10nm) passivation layers. A custom-built apparatus and specimens fabricated through MEMS process were utilized to perform micro-tensile tests. Passivation effect was observed under monotonic and cyclic loading, and investigated how it affects the bahavior of metal films with and without annealing. Stress-strain curves show an increase in elongation for passivated metal films, which is attributed to delay in the strain localization due to constraint imposed by the ultra-thin passivation layer.

The Mechanical Behavior of Passivated Al and Al-C Thin Films: Hojang Kim1; Injong Oh1; Gi-Dong Sim1; 1KAIST
    In this presentation, we report the mechanical behavior of passivated Al and Al-C thin films. Mechanical characterization was carried out by performing tensile tests and membrane deflection tests. The Young’s modulus and the yield strength measured from both methods show similar results. Al thin films containing 4.5 at.% carbon exhibit the yield strength of ~400 MPa, which is significantly larger compared to the yield strength of pure Al thin films (~170 MPa). The mechanical behavior of passivated/unpassivated freestanding Al and Al-C thin films was measured up to a strain range of ~10%. When a thick passivation layer (40 nm) is deposited, a large decrease in the failure strain occurs. However, a large increase in the failure strain can be shown when an ultra-thin passivation layer (< 10 nm) is deposited. The relation between surface roughness and passivation effect will also be discussed.

A Rapid Testing Method for Evaluating Strain-path Sensitivity: Anastasia Vrettou1; David Collins1; 1University of Birmingham
    Evaluating ductility from different strain-paths is typically limited by the number of specimens that can be feasibly tested by methods such as Nakajima testing. Evaluating only selected pre-strains, for example, poorly samples strain-space, which must inhibit the discovery of the most desirable deformation paths. This shortcoming is overcome with a bespoke Small Punch Testing (SPT) system equipped with Digital Image Correlation, where ~10mm diameter specimens (scaled Nakazima geometries) are rapidly tested. The method is showcased steel specimens, where the strain-path sensitivity is comprehensively described. The specimen geometry permits electron microscopy without further sample machining; interrupted SPTs tests were examined with EBSD to obtain texture and Geometrically Necessary Dislocation density for different macroscopic strains and strain-paths. Complementary characterisation shows that texture development and dislocation density & structure, with the latter exhibiting unambiguous differences between equivalent strains reached by dissimilar strain-paths.