Advanced Thermo-mechanical Characterization of Materials with Special Emphasis on In Situ Techniques: In Situ Techniques V
Sponsored by: TMS Structural Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Nanomechanical Materials Behavior Committee, TMS: Thin Films and Interfaces Committee
Program Organizers: Amit Pandey, LG Fuel Cell Systems Inc.; Sanjit Bhowmick, Hysitron; Jeff Wheeler, ETH Zurich; María Teresa Pérez Prado, IMDEA Materials Institute; Robert Wheeler, MicroTesting Solutions LLC; Josh Kacher, Georgia Tech

Wednesday 8:30 AM
March 1, 2017
Room: 32A
Location: San Diego Convention Ctr

Session Chair: Vikas Tomar, Purdue; Jagannathan Rajagopalan, Arizona State University

8:30 AM  
Site-Specific Mechanical Evaluation Using Microscale Samples Tested In Situ within SEM and XCT: Jack Donoghue1; Robert Wheeler2; Bartlomiej Winiarski1; Albert Smith1; Alistair Garner1; Ziang li Zhong1; M. G. Burke1; Timothy Burnett1; Philip Withers1; 1University of Manchester; 2MicroTesting Solutions LLC
    Mechanical testing on the 10-5–10-3m length scale is necessary for both understanding deformation at the grain scale level as well as the bulk properties of fine grained materials with a small representative volume, such as low penetration depths with irradiation studies. Focused Ion Beam (FIB) milling is invaluable for the manufacture of samples at such specific sites but conventional Ga+ FIB becomes impractical at the larger end of this length scale. Here we employ the recently developed Xe+ Plasma FIB (PFIB) for the production of larger samples with the additional advantage of reduced surface damage. The PFIB is used to produce tensile samples of ~100μm gauge length to evaluate the effect of proton irradiation of steels. These samples are mechanically evaluated using a novel micro-mechanical testing rig that allows for loads up to 450g to be applied in situ within Scanning Electron Microscopes (SEM) and X-ray Computed Tomography (XCT) equipment.

8:50 AM  
Understanding the Local Ligament-level Deformation Response in Unit Cell Lattices: H. Carlton1; J. Lind1; N. Volkoff-Shoemaker1; M. Messner1; H. Barnard2; N. Barton1; M. Kumar1; 1Lawrence Livermore National Laboratory; 2Lawrence Berkeley National Laboratory
    Recent interest has focused on lattice structures with remarkable strength-to-weight ratio that can be produced with metals by the additive manufacturing process. While much attention is devoted to the performance of the underlying base material, non-uniform partitioning of stress is common in these structures and varies depending on the geometry and topology of the structure itself. This study reports on high resolution mapping of the heterogeneous structural response of single unit cells during macro-scale deformation. Two different types of structures were evaluated using compression tests coupled with in-situ synchrotron micro-tomography. Computational modeling efforts were performed taking into account defects and evaluating micro-strain responses as well as capturing the load-displacement response. Local strain measures, obtained from the in-situ tomography, were also captured and compared well with the model. This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

9:10 AM  
Extraction of Crystal Plasticity Parameters of IN718 Using High Temperature Microcompression: Bin Gan1; Aitor Cruzado2; Marcos Jiménez2; Koldo Ostolaza3; Arantza Linaza3; Javier Segurado2; Javier Lloca2; Jon Molina2; 1Northwestern Polytechnical University; 2IMDEA Materials Institute; 3Industria de TurboPropulsores
    Ni-based superalloys are widely utilized in structural applications in aeroengine, owing to their exceptional mechanical properties in corrosive and oxidizing environments. In the present investigation, site-specific micropillars with the diameter varying from 1 um to 18 um were milled out by Focused Ion Beam from a polycrystalline IN718 superalloy specimen and then measured with high temperature micro-compression techniques up to 575 ºC. The effects of pillar size, pillar orientation, strain rate and temperatures were quantitatively assessed. The different hardening behavior for single-slip, co-planar, non co-planar double slip and multiple-slip conditions were investigated. The testing results were used to determine the crystal plasticity parameters of a phenomenological crystal plasticity (CP) model of IN718 superalloy that were then used in a polycrystalline finite element model of this alloy. This new model was able to predict, without fitting any parameter, the experimental macroscopic compression test with an error below 5%.

9:30 AM  
In-Situ Thermo-mechanical Characterization of Serrated Flow in Nanostructured Binary Mg-Al Alloys: Marta Pozuelo1; Yuan-Wei Chang1; Sanjit Bhowmick2; Jaime Marian1; Jenn-Ming Yang1; 1UCLA; 2Hysitron, Inc.
    Serrated flow, also known as the Portevin-Le Chatelier effect, has been extensively investigated in binary Mg-alloys such as Mg-Ag, Mg-Y and Mg-Li alloys. Interestingly, however, this effect has not been observed in Mg-Al alloys. In this work, we reveal the appearance of serrations in nanostructured Mg-Al alloys processed by cryomilling and spark plasma sintering during in-situ SEM microcompression tests at room temperature and strain rates between 2×10-3 and 10-1 s-1. The observed serrated stress-strain behavior is attributed to the dynamic strain aging by which interstitial O and/or N impurities introduced during cryomilling diffuse and interact with in-grown dislocations during deformation. By making use of in-situ SEM microcompression tests at high temperatures, we aim to determine the optimal temperature and strain rate conditions where serrations appear, which in the end must be avoided for an optimized mechanical performance of structural materials.

9:50 AM Break

10:10 AM  
In-SEM Microscale Mechanical Testing of Thin Film Plastic Flow and Interfacial Integrity: Yang Mu1; Xiaoman Zhang1; Wen Meng1; 1Louisiana State University
     Quantitative measurements of plastic flow in thin films under simple and well defined deformation geometries are important for calibration and validation of microscale plasticity models. Quantitative measurements of critical stresses needed to affect interfacial mechanical failure in coating/substrate systems are likewise important for engineering durable coated mechanical components and manufacturing tools.We present recent results on quantitative evaluation of thin film plastic flow and coating/substrate interfacial mechanical integrity. We utilize a new, in-SEM, micro-pillar axial compression testing protocol to achieve quantitative measurements of confined plastic flow in metal thin films and critical stresses for affecting shear failures of coating/substrate interfaces. Dependence of flow stress on film thickness and microstructure, and dependence of interfacial shear failure stress on the choice of interfacial adhesion layers between ceramic coatings and substrates will be reported. Relevance of the results and testing protocol to microscale plasticity models and surface engineering practices will be discussed.

10:30 AM  
In-situ Analysis of the Tensile Deformation Modes and Anisotropy of Extruded Mg-10Gd-3Y-0.5Zr (wt.%) at Elevated Temperatures: Huan Wang1; Carl Boehlert2; Qudong Wang1; Dongdi Yin3; W Ding1; 1Shanghai Jiao Tong University; 2Michigan State University; 3Southwest Jiaotong University
    The deformation modes and anisotropic behavior during the tensile deformation of extruded Mg-10Gd-3Y-0.5Zr (wt.%) at 200, 250 and 300oC were investigated using in-situ SEM. The samples tested along the extrusion direction (ED) exhibited higher strength than that for the samples perpendicular to the ED (TD) and the samples oriented 45o to the ED. Dislocation slip was the main deformation mode during the tensile deformation, while GBS contributed at 300oC. No twinning was observed. Non-basal slip accounted for 21%, 7% and 36% of the total active slip systems at 200oC for the ED, TD and 45o samples, respectively. The non-basal slip contribution was 12~17% at 250oC, and it decreased to 3~5% at 300oC. Multiple-slip within grains and slip transfer across grain boundaries were frequently observed at 200 and 250oC. Intergranular cracks were more likely to initiate at the boundaries where the neighboring grains were in hard orientations for basal slip.

10:50 AM  
Dislocation Shielding as a Function of Temperature in Microscale Silicon Bending Beams: Eric Hintsala1; Sanjit Bhowmick1; S. A. Syed Asif1; William Gerberich2; 1Hysitron, Inc.; 2University of Minnesota
    Using focused ion beam machined microscale bending specimens, fracture initiation and crack extension for silicon as a function of temperature was evaluated. This was done utilizing a doubly-clamped three point bending geometry, which naturally arrests nucleated cracks due to the changing stress intensity with crack length. This technique is useful for post-mortem evaluation through a variety of methods, but here, thinning using focused ion beam and post-mortem TEM was utilized. Of particular interest is determining the influence of dislocations as a function of temperature on shielding and a corresponding changes in the applied stress intensity factor necessary to produce a cracking event. The most common and easiest method is to produce pre-notches using the focused ion beam, however these possess a radius of curvature and do not represent a true fracture toughness. These are compared against a novel method to produce natural precracking in the specimen.