Advanced Characterization Techniques for Quantifying and Modeling Deformation: Session III
Sponsored by: TMS Extraction and Processing Division, TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Materials Characterization Committee
Program Organizers: Rodney McCabe, Los Alamos National Laboratory; Marko Knezevic, University of New Hampshire; Irene Beyerlein, University of California, Santa Barbara; Wolfgang Pantleon, Technical University of Denmark; C. Tasan, Massachusetts Institute of Technology; Arul Kumar Mariyappan, Los Alamos National Laboratory; Olivia Underwood Jackson, Sandia National Laboratories
Tuesday 8:30 AM
March 16, 2021
Room: RM 13
Location: TMS2021 Virtual
8:30 AM
Characterization and Modeling of Deformation Twinning in Mg during Compression and Tension: Zhe Chen1; Mohammadreza Yaghoobi1; Veera Sundararaghavan1; John Allison1; Samantha Daly2; 1University of Michigan; 2University of California, Santa Barbara
The twinning and detwinning behavior in magnesium alloys was characterized during in-situ compression followed by tension. Full-field deformation was measured by combined use of scanning electron microscopy and digital image correlation (SEM-DIC). Twinning was identified by clustering and computer vision applied to the deformation data. Statistical analysis was performed to investigate the effect of microstructure on twinning nucleation and growth. The nominal Schmid factor exhibited the most significant effect on twinning, while the effects of other metrics including the m’ factor, the residual burgers vector, and neighbor strain accommodation was insignificant. A new rate-independent crystal plasticity finite element (CPFE) model using the open-source, high performance PRISMS-Plasticity CPFE framework was used to simulate these experiments. The contributions of the stresses inside both parent grain and twinned children were considered to simulate the effects of microstructure on twinning. The strain and twin maps of SEM-DIC were well-simulated by the PRISMS-Plasticity CPFE model.
8:50 AM
Recent Advances in Applying In-situ Electron Microscopy for Local Determination of Crack Processes: Daniel Kiener1; Markus Alfreider1; Inas Issa1; Michael Wurmshuber1; Michael Burtscher1; Klemens Schmuck1; 1University of Leoben
Failure due to crack initiation and propagation is a dramatic event with an intrinsically local nature. In-situ electron microscopy is therefore ideally suited to detail the nanoscale deformation and failure processes occurring at crack tips or in their vincinity. In the present contribution, we will highlight recent advances in scale bridging fracture tests from the macroscale down to the micro- and nanometer level by conducting quantitative miniaturized fracture experiments inside scanning and transmission electron microscopes. Employing recent advances such as continuous stiffness evaluation, digital image correlation or local strain mapping, we will demonstrate the rich information that can be extracted from such kinds of experiments to detail, for example, the local stress state near the crack tip as well as individual dislocation processes and shielding events occurring in the vicinity of the crack. Furthermore, the influence of specific interfaces on the crack propagation will be addressed.
9:10 AM Invited
Materials Science Applications of Four Dimensional–scanning Transmission Electron Microscopy (4D-STEM): Colin Ophus1; 1Lawrence Berkeley National Laboratory
With the introduction of high speed direct electron detectors, scanning transmission electron microscopy (STEM) can now record a full image of the diffracted electron probe scanned over the sample, producing a four-dimensional dataset we refer to as a 4D-STEM experiment. These diffraction images of the electron probe are extremely rich in atomic-scale information, such as the sample structure, orientation, composition, phonon spectra, defect structure and more. In this talk, I will discuss several 4D-STEM applications in materials science. I will show several examples of nanobeam electron diffraction used to measure sample structure, orientation and strain, for samples ranging from metallurgical alloys to conductive polymers. I will also describe phase contrast imaging methods such as differential phase contrast, ptychography and STEM holography. Each of these analyses can be performed with our open source py4DSTEM code.
9:40 AM
Study of Slip Transmissibility and Its Correlation to Local Geometrically Necessary Dislocation Content in Grade 1 Pure Titanium: Harsha Phukan1; Thomas Bieler1; Ruqing Xu2; Philip Eisenlohr1; Martin Crimp1; Carl Boehlert1; 1Michigan State University; 2Argonne National Laboratory
Using in-situ differential aperture x-ray microscopy analysis, a polycrystalline specimen of titanium with a soft texture favoring prism <a> slip was subjected to incremental four-point bending. The geometrically necessary dislocation (GND) content in several grain boundary regions was analyzed during hold times. Based on orientation gradients resulting from plastic deformation, total and slip system specific GND densities were calculated at the second bending increment (approximately 1.7% bulk strain). The propensity of slip transfer across a grain boundary is assessed using the Luster-Morris parameter and residual Burgers vector. In most cases, low transmissibility of slip can be directly correlated to pileups of GNDs of the slip systems with high resolved shear stress. Furthermore, the agglomeration of GNDs is significantly influenced by the local stress state, which differs significantly and varies spatially from the global stress state. Supported by DOE/BES grant DE-FG02-09ER46637; APS supported by DOE contract DE-AC02-06CH11357.
10:00 AM
Study of the Effect of Grain Boundary Parameters on the Micro Hall-Petch Slope in Mg Alloys: Mohsen Taheri Andani1; Aaditya Lakshmanan1; Veera Sundararaghavan1; John Allison1; Amit Misra1; 1University of Michigan
Theoretical studies have shown that the geometry and structure of grain boundaries (GBs) in metallic materials play a significant role in determining the Hall-Petch slope. However, experimental capabilities to assess the GB strength to validate these studies are still limited. The objective of this work is to utilize a high-resolution electron backscatter diffraction technique coupled with a dislocation pile-up model to estimate the barrier strength of specific GBs to specific slip systems, referred to as the micro Hall-Petch slope. The micro Hall-Petch slopes are then correlated with geometric descriptors of the respective GBs. The results indicate that the angle between the two slip plane traces on the GB plane and the angle between the slip directions are the most sensitive parameters affecting the micro Hall-Petch slope. This research will provide new insights into the understanding of the grain refinement strengthening parameters in the plasticity of Mg alloys.
10:20 AM
Recent Advances in Bragg Coherent Diffraction for Nanoscale Imaging of Strain: Ross Harder1; 1Argonne National Laboratory
Bragg Coherent Diffraction Imaging (BCDI) offers nanoscale resolution imaging with high sensitivity to distortions of the sample lattice. This talk will introduce the technique and describe recent improvements at the BCDI instrument of the Advanced Photon Source (APS) for imaging submicrometer scale crystalline objects. The new capability enables in-situ determination of crystallographic orientation via broadband Laue Diffraction Microscopy. With the full knowledge of the orientation of a specific sub-micrometer scale crystal one can measure coherent diffraction around multiple Bragg peaks of the lattice. With such data sets the full strain tensor of the sample can be imaged with tens of nanometer resolution at current generation synchrotrons. The pending upgrades to machines like the APS will significantly improve the capabilities of coherent techniques. We anticipate sub nanometer scale resolution imaging at the new instruments being developed.
10:40 AM
Towards Accurate Absolute Stress and Orientation Measurement by Electron Backscatter Diffraction: Tijmen Vermeij1; Johan Hoefnagels1; 1Eindhoven University of Technology
We explore the potential of using a new form of Electron Backscatter Diffraction (EBSD) by combining Integrated Digital Image Correlation, a well-established tool in experimental mechanics for highly accurate identification of e.g. material properties, with High angular Resolution EBSD, a well-established tool to attain local relative stresses. Through a rigorous derivation of the optimization scheme, employing brightness conservation between EBSD patterns (EBSPs), a direct one-step correlation of the maximum overlapping field-of-view of the EBSPs is achieved. Furthermore, crystal symmetry, out-of-plane-stress state and co-correlation of detector geometry are fully exploited, yielding simultaneous correlation of all overlapping regions of interest in multiple intergranular EBSPs. As a result, accurate measurement of absolute stress, crystal orientation and EBSD geometry, using limited assumptions, is demonstrated on a virtual polycrystalline case-study, showing errors below 10E-4 in elastic strain and 7E-5 rad in orientation, without using simulated EBSPs as reference; experimental validation is underway.