Mechanical Response of Materials Investigated through Novel In-situ Experiments and Modeling: Session II
Sponsored by: TMS Structural Materials Division, TMS: Thin Films and Interfaces Committee
Program Organizers: Saurabh Puri, VulcanForms Inc; Amit Pandey, Lockheed Martin Space; Dhriti Bhattacharyya, Australian Nuclear Science and Technology Organization; Dongchan Jang, KAIST; Jagannathan Rajagopalan, Arizona State University; Josh Kacher, Georgia Institute of Technology; Minh-Son Pham, Imperial College London; Robert Wheeler, Microtesting Solutions LLC; Shailendra Joshi, University of Houston
Tuesday 2:00 PM
February 25, 2020
Room: 33A
Location: San Diego Convention Ctr
Session Chair: Josh Kacher, Georgia Institute of Technology; Jedsada Lertthanasarn, Imperial College London
2:00 PM Introductory Comments
2:10 PM Invited
In-situ TEM Investigation on Pyramidal Dislocations in Magnesium: Boyu Liu1; Fei Liu1; Bin Li2; Jian-Feng Nie3; Zhi-Wei Shan1; 1Xi'An Jiaotong University; 2University of Nevada; 3Monash University
Magnesium is the lightest structural metal with promising applications for achieving energy efficiency. However, magnesium has limited ductility, which imposes severe constraints on cost-sensitive processing and hampers its widespread applications. The ductility of magnesium is intimately related to pyramidal dislocations. Controversies abound surrounding the fundamental behavior of pyramidal dislocations, such as their ability to accommodate plastic strain and their slip pathways, causing difficulties in rationalizing the mechanical behavior and in alloy design. The present work exploits in-situ TEM mechanical testing and 3D image reconstruction to study the pyramidal dislocations in magnesium. We demonstrate that pyramidal dislocations can accommodate considerable plasticity through gliding on both pyramidal I and II planes. Our findings provide information on the mobility of pyramidal dislocations and its relationship with plasticity in pure Mg of small sizes. Our experimental strategy can be extended to understanding the dislocation behaviors in other hexagonal metals.
2:40 PM
Deformation Behavior of Additively Manufactured Cu-Fe Composites at Different Strain Rates: Arya Chatterjee1; Ethan Sprague1; Benjamin Derby1; Jyoti Mazumder1; Amit Misra1; 1University of Michigan
The present investigation aims to study the plastic deformation response an immiscible Cu-BCC system material. The biphasic (FCC-BCC) Cu-BCC system used in the current study is Cu-Fe composite. Cu-Fe composites are prepared by additive manufacturing (AM) process using laser direct metal deposition (DMD) technique. Different AM Cu-Fe composites are then subjected to plastic deformation at different strain rates. Nano-indentation technique is used to apply different strain rate deformation to the Cu-Fe composites. Post deformation damages specifically at interfaces are studied with the help of transmission electron microscopy to elucidate the underlying mechanism of deformation at different strain rates.
3:00 PM Invited
Investigating Bulk Mechanical Properties on a Micro-scale: Micro-tensile Testing of Ultrafine Grained Ni-SiC Composite to Determine its Fracture Mechanism and Strain Rate Sensitivity: Dhriti Bhattacharyya1; Alan Xu1; Chao Yang1; Gordon Thorogood1; Michael Saleh1; 1Australian Nuclear Science and Technology Organization
In-situ micro-tensile tests were performed to investigate the mechanical properties of ultrafine grained Ni-3wt% SiC composite. The objective was to understand the sample size effect on the mechanical properties of the composite and the reasons for the low ductility of the bulk composite. Dog-bone micro-tensile samples were manufactured using a Focused Ion Beam instrument to dimensions of 15 µm length by 5 µm (w) by 5 µm (h). The samples were tested in tension at a low strain rate (LSR) of 0.000087/s and a relatively higher strain rate (HSR) of 0.011/s. The LSR tests produced yield stress, ultimate tensile stress and modulus values that approach those previously reported for bulk/macro-level tensile tests. However, the elongation and fracture energy at the micro-level was approximately half that at the bulk scale. This discrepancy is attributed to unwanted carbon and silicon oxide impurities ~1.5 µm in diameter which act as stress concentrators.
3:30 PM Break
3:50 PM Keynote
Core Structure and Mobility of <c+a> Dislocations in Alpha-Ti: Satish Rao1; Adam Pilchak2; Christopher Woodward2; 1Ues Inc.; 2Air Force Research Laboratory
Toward a goal of understanding of fatigue crack propagation in alpha-Titanium alloys, the MEAM spline potential of Hennig et.al. was used to determine the planar fault energies on basal, prism, pyramidal planes and <a> screw dislocation core structure in pure alpha-Ti. It was found that the MEAM-spline potential gives fault energies and <a> screw dislocation core structure in fairly good agreement with first principles calculations. It has been used in this talk to determine the core structure and mobility of <c+a> dislocations in pure alpha-Ti. The minimum energy core structure for <c+a> screw dislocations is dissociated on the pyramidal 1 plane. At 300 and 600K, the screw dislocation moves by a regular Peierls mechanism with critical stresses of the order of 0.005G. The mixed dislocation with <100> line direction is climb dissociated on the basal plane. Such simulation results are compared with experimental yield stress data for pure alpha-Ti.
4:30 PM
Ab-initio Predictions of Plastic Anisotropy in BCC Metals: Lucile Dezerald1; Antoine Kraych2; Emmanuel Clouet3; Bassem Ben Yahia1; Lisa Ventelon3; Francois Willaime3; David Rodney2; 1Institut Jean Lamour; 2Institut Lumiere Matiere; 3CEA Saclay
Body-centered cubic (BCC) metals are known for their atypical plasticity at low temperatures. Here, we focus on their plastic anisotropy, also known as Schmid law deviation, which arises from ½<111> screw dislocation core effects. We use ab initio Density Functional Theory calculations to investigate the link between screw dislocation core properties and Schmid law deviation in BCC metals. We find that the dislocation trajectory systematically deviates from the average glide plane, leading to the well-known twinning/antitwinning asymmetry. Furthermore, we show that the dislocation core deformation modeled with eigenstrains is directly linked to the effect of non-glide stresses. We calculate with DFT the dislocation trajectory and eigenstrain in the absence of stress, and these values are used to predict Schmid law deviation in BCC metals. These results are validated by comparison with DFT calculations performed under shear and non-glide stresses, and our predictions are compared to the available experimental data.
4:50 PM Cancelled
Combined In-situ Lattice Imaging and MD Modeling on Dislocation and Twinning Nucleation: Scott Mao1; 1University of Pittsburgh
Structural nanomaterials and nanocomposites have excellent mechanical performance, which can be tuned through both structural architecture and material size effects. However, the behavior of individual component normally sized at 5-50 nanometers in the structural nanomaterials is key important, has not been explored before. This talk will be the in-situ mechanics for studying the mechanical behavior at atomistic scale for 5 to 50 nanometer-sized pillars (so called lattice pillar) of metallic crystals. Combined molecular dynamics with the in-situ high resolution transmission electron microscope is going to open a new approach to directly characterize atomic-scaled deformation with in-situ mechanics for such small sized pillar. I will cover the stress-strain behavior, high stress induced lattice disturbance, dislocation dipole nucleation and competition between slip and twinning in the deformation process, which potentially can be related to individual component of structural nanomaterials such as nano-porous and nano-lattice materials.