Advanced Characterization Techniques for Quantifying and Modeling Deformation Mechanisms: Session III
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Shaping and Forming Committee
Program Organizers: Rodney McCabe, Los Alamos National Laboratory; John Carpenter, Los Alamos National Laboratory; Thomas Beiler, Michigan State University; Khalid Hattar, Sandia National Laboratory; Wolfgang Pantleon, DTU; Irene Beyerlein, Los Alamos National Laboratory

Tuesday 8:30 AM
February 28, 2017
Room: 33C
Location: San Diego Convention Ctr

Session Chair: Philip Eisenlohr, Michigan State University; Søren Schmidt, Technical University of Denmark

8:30 AM  Invited
3D Orientation Mapping in the Transmission Electron Microscope: Søren Schmidt1; Peter Mahler Larsen1; Hossein Alimadadi1; Takeshi Kasama1; Xiaoxu Huang1; 1Technical University of Denmark
    The 3D Orientation Mapping in the Transmission Electron Microscope (3D-OMiTEM) technique enables characterization of nano-crystalline materials in the form of 3D grain maps with a spatial resolution of a few nm. The thickness of the sample is typically 100 nm. The method utilizes conical dark field scanning mode for data acquisition, where images are collected over a wide range of beam and sample tilts. Since the methodology is non-destructive structural 3D evolution of the nano-structure, arising e.g. from external annealing or deformation, can potentially be monitored. Here, we present the methodology, algorithms and latest applications.

8:50 AM  
Shear-Coupled Grain Growth and Texture Development in a Nanocrystalline Ni-Fe Alloy during Cold Rolling: Li Li1; Tamas Ungar2; L Toth3; Z Skrotzki4; Y Ren5; Zs Fogarassy6; X.T. Zhou1; Peter Liaw7; 1Shanghai Institute of Applied Physics-Chinese Academy of Science; 2Eötvös University Budapest; 3Université de Lorraine; 4Technische Universität Dresden; 5Argonne National Laboratory; 6Hungarian Academy of Science; 7The University of Tennessee
    The evolution of texture, grain size, grain shape, dislocation and twin density has been determined by synchrotron X-ray line profile analysis in a nanocrystalline Ni-Fe alloy after cold rolling along different directions related to the initial fiber and the long axis of grains. The texture evolution has been simulated by the Taylor-type relaxed constraints viscoplastic polycrystal model. The simulations were based on the activity of partial dislocations in correlation with the experimental results of dislocation density determination. The concept of stress-induced shear-coupling is supported and strengthened by both the texture simulations and the experimentally determined evolution of the microstructure parameters. Grain-growth and texture evolution are shown to proceed by the shear-coupling mechanism supported by dislocation activity as long as the grain size is not smaller than about 20 nm.

9:10 AM  
Unambiguous Complexion Identification and Inspection in High Purity Binary Alloy Systems: Jennifer Schuler1; Timothy Rupert1; 1University of California Irvine (UCI)
    Complexions are thermodynamically-stable interfacial structures that can potentially be used to control the behavior of nanostructured materials. This talk demonstrates methods for controlled complexion formation, by obtaining full characterization of the resulting interfacial structures and exploring the effect of processing variables. Binary alloys systems such as Cu-Zr, Cu-Fe and Cu-Mo were used to form a range of complexion types with sputter deposition and appropriate heat treatments. Electron backscattered diffraction and transmission Kikuchi diffraction are used in conjunction with high resolution transmission electron microscopy to provide a detailed picture of the boundary structure and chemistry. Preliminary in situ nanoindentation experiments show that complexion type and mechanical behavior are closely related. Similarly, radiation tolerance is connected to complexion structure through the use of in situ self-ion irradiation experiments. As a whole, this work shows that intelligent control of boundary structure is a promising materials design strategy for optimizing different types of properties.

9:30 AM  
In Situ TEM Compression Testing of IN718 Fabricated by Electron Beam Melting: Kinga Unocic1; Michael Kirka1; Ryan Dehoff1; 1ORNL
    Fabrication of nickel base alloys via electron beam melting with equiaxed grain structure is challenging. Here we report, by monitoring the deformation of submicron-sized equaixed and textured grain structure of IN718 compressed normal to its {001}, {011}, {111} planes with transmission electron microscopy. IN718 was fabricated via electron beam melting with two different microstructures; equaixed and textured along building direction. First the orientation of the grains were identified via electron backscattered diffraction analysis, followed by extraction of specimens from the grains with desired orientations using focus ion beam milling for compression testing. The compression testing was performed with Hysitron PI95 TEM Picoindentor holder and the effect of grain type as well grain orientation on mechanical response will be discussed.

9:50 AM Break

10:10 AM  
Characterization and Deformation Behavior of Microstructural Gradients in the Low Solvus High Refractory (LSHR) Nickel Base Superalloy : Samuel Kuhr1; Gopal Viswanathan1; Hamish Fraser1; 1The Ohio State University
    LSHR hybrid disks were fabricated using a dual microstructure heat treatment (DMHT) that produced a microstructural gradient from the bore to the rim, designed to enhance site specific properties of the turbine disks. In this investigation, the gradient transition region was studied to understand how various gamma prime sizes and distributions influence its mechanical properties. As-received, solution treated and solution treated and aged (STA), microstructural gradients were tensile tested at room temperature and characterized. Tensile testing was performed in conjunction with digital image correlation (DIC) to determine bulk and localized strains. Characterization of gamma prime morphology was performed using HR-SEM. The natures of the various deformation substructures were examined by TEM. DIC measurements were successful in showing strain localization in all of the gradient microstructures examined, however a simple relationship correlating strain to grain size and gamma prime morphology was not apparent.

10:30 AM  
Atomic Resolution Energy Dispersive X-ray Spectroscopy of Segregation Along SESFs in Ni-Based Disk Alloys: Timothy Smith1; Bryan Esser1; Nikolas Antolin1; Robert Williams1; Andrew Wessman2; Hamish Fraser1; Wolfgang Windl1; David McComb1; Michael Mills1; 1The Ohio State University; 2GE Aviation
    Local compositional and structural changes occurring in association with stacking faults in two different Ni-base disk superalloys were characterized and related to the possible rate-controlling processes during creep deformation at intermediate temperatures. These rate-controlling processes are not presently understood. Compression creep tests on specially prepared single crystals of ME3 and ME501 were conducted at 760°C in the [001] orientation in order to promote precipitate shearing by stacking faults and microtwins. Energy dispersive X-ray spectroscopy using a probe corrected STEM has revealed differences in compositional variation along the extrinsic faults inside the precipitates between the two alloys. VASP modeling and HAADF image simulations show lower SESF energy to be the driving force for these compositional variations. This analysis also revealed Cottrell atmospheres surrounding the Shockley partials during precipitate shearing, as well as moiré-like contrast associated with surface oxidation. Implications of these results with respect to rate-controlling deformation mechanisms are discussed.

10:50 AM  
How Important are the Smallest Grains for their Aggregate Mechanics?: Tias Maiti1; Philip Eisenlohr1; 1Michigan State University
    High Energy X-Ray Diffraction Microscopy (HEDM) is a nondestructive way of characterizing orientations, lattice strains, and grain morphology in polycrystalline materials. HEDM with near-field detector position is akin to tomography and therefore sensitive to grain shape but does not resolve lattice strains. The complementary far-field approach resolves lattice strains but only detects grain centers-of-gravity and relative sizes. Due to the overall diffracted intensity scaling with grain size, the population of smallest grains carries the largest uncertainty, in particular when using the far-field approach. To determine the influence of uncertainty in detecting smaller grains on the kinematic response of easier-to-detect large grains, Crystal Plasticity Fast Fourier Transform (CPFFT) full-field simulations of artificial microstructures with grain size distributions similar to experimental data but omitting fractions of small grains are statistically compared. The average response of larger grains is mostly insensitive to small ones.

11:10 AM  
The Origin of Stochastic Behavior during Nanoindentation near a Grain Boundary in Cu: Benjamin Schuessler1; Mehdi Hamid1; Pui Ching Wo1; Hussein Zbib1; 1Washington State University
    Mechanical responses in materials during nanoindentation are often stochastic. Our recent work demonstrated that grain boundaries play an important role in the stochastic nature of mechanical responses during nanoindentation in Cu. However, how a grain boundary interacts with the deformation associated with a nearby nanoindent is not clear. In this study, experiments and simulations were performed to gain better understanding on the origin of stochastic behavior during nanoindentation near a grain boundary. The material pile-up and plastic deformation around indents that are close to and far away from a grain boundary were experimentally studied using scanning probe and scanning electron microscopy. Whereas the evolution of dislocation structure during nanoindentation and their interaction with a grain boundary were visualized using 3D discrete dislocation dynamics simulation. A model is also developed to study the influence of individual dislocation preexisting in the material on the stochastic behavior during nanoindentation near a grain boundary.

11:30 AM  
Improved Angular and Spatial Resolution of Measured Lattice Rotations in Highly Deformed Bulk Materials through Combining Low-kV EBSD with the Dictionary Indexing Approach: Ali Gholinia1; Timothy Burnett1; Bart Winiarski1; Farangis Ram2; Saransh Singh2; Marc De Graef2; 1University of Manchester; 2Carnegie Mellon University
    If the EBSD spatial resolution can be improved, the technique will become superior to TEM analysis for deformation microstructure measurements in that it is fully automated, can measure large areas, and has no sample thickness limitations. Lowering the microscope voltage improves the spatial resolution, but this does not solve the problem of quantifying a highly deformed microstructure; the number of points whose orientations can be determined by the standard Hough-transform analysis decreases from 95% at 20kV to 5% at 5 kV in a shot-peened Al sample. To address this issue, we decrease the capture angle from 90° to 70° and use a dictionary indexing technique which can determine the orientation of 85% of points at 5 kV. We have improved the effective spatial resolution of EBSD, so that details of the deformed microstructure (multi-walled grain and sub-grain boundaries) are revealed that could not be imaged and quantified by EBSD before.