Mechanical Response of Materials Investigated Through Novel In-Situ Experiments and Modeling: Session III
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, VulcanForms Inc; 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

Tuesday 8:00 AM
March 1, 2022
Room: 206B
Location: Anaheim Convention Center

Session Chair: Benjamin Eftink, Los Alamos National Laboratory; Sourav Das, University Of Illinois, Urbana-Champaign

8:00 AM
Dwell Fatigue in Ti Alloys; TEM on Dislocations, HEDM, alpha2-Ti3Al and SAXS: David Dye¹; Sudha Joseph¹; Felicity Dear¹; Yilun Xu¹; Rachel Lim²; Thomas McAuliffe¹; Joel Bernier³; Darren Pagan²; Phani Karamched⁴; Kate Fox⁵; David Rugg⁶; Fionn Dunne¹; ¹Imperial College; ²Penn State University; ³Lawrence Livermore National Laboratory; ⁴Oxford University; ⁵Rolls-Royce plc; ⁶formerly Rolls-Royce plc
    Dwell fatigue has been concerning for >50y and still causes failures which provide interesting insights. High Al contents have long been implicated, through short range ordering and/or the precipitation of Ti3Al causing <a> slip localisation, which can be tracked through SAXS and APT; Ti3Al precipitation may be vacancy-nucleated [Dear et al, Acta Mater 212:116811, 2021]. The existence of long paths for easy <a> slip in critically stressed volumes, e.g. macrozones, is also held to be important, which makes large volume forgings a particular concern. Hypothesis-driven experimentation through the production of samples specifically designed to contain the microstructural feature of concern, is capable of reproducing the large reductions in dwell strength observed in the field [Joseph et al, Int J Plasticity 131:102473, 2020; Xu et al, Nature Commun 11:5868, 2020]. In situ High Energy Diffraction Microscopy on slip avalanches also provides insights into the beneficial role of O vs Al.

8:20 AM
NOW ON-DEMAND ONLY - Correlating the Microstructure of Friction-stir Processed Al 7085 to Mechanical Properties Using In-situ Micromechanical Testing: Tanvi Ajantiwalay¹; Christian Roach¹; Hrishikesh Das¹; Mert Efe¹; Piyush Upadhyay¹; Arun Devaraj¹; ¹Pacific Northwest National Laboratory
    Local mechanical properties of industrially relevant lightweight Aluminum alloys such as 7085 can be significantly modified by using friction stir processing (FSP). FSP involves application of severe shear deformation, which leads to highly refined dynamically recrystallized grains, unique precipitation and shear deformation induced textures. In this study, the microstructural modification achieved by FSP of Al7085 alloy is revealed using systematic transmission electron microscopy and atom probe tomography studies. This detailed understanding of the microstructure is then correlated to the mechanical properties via in-situ nanoindentation and micro-pillar compression using PI89 Picoindenter inside a plasma focused ion beam (PFIB). The specimens fabricated using the PFIB eliminates gallium implantation in Al, which is inherent to Ga-based FIBs. This direct correlation of local mechanical properties to corresponding microstructures can enable “right property at the right place” approach in component design of lightweight alloys.

8:40 AM
High Strength Nanocrystalline CoAl Intermetallics with Room Temperature Deformability: Xinghang Zhang¹; Ruizhe Su¹; Dajla Neffati²; Yashashree Kulkarni²; ¹Purdue University; ²University of Houston
    Intermetallics have high strength, but are often brittle at room temperature. Here we present a deformable nanocrystalline CoAl intermetallics. In situ micropillar compression studies show that nanocrystalline CoAl exhibits ultra-high yield strength, exceeding 4.5 GPa, much higher than that of traditional coarse grained and nanocrystalline B2 intermetallics. Surprisingly, nanocrystalline CoAl intermetallics also shows prominent work hardening to a flow stress of 5.7 GPa up to 20% compressive strain. Transmission electron microscopy studies show that deformation induces abundant dislocations inside CoAl grains, which accommodate plastic deformation. Molecular dynamics simulations reveal unique deformation mechanisms of the nanocrystalline intermetallics.

9:00 AM  Invited
Three-dimensional Dislocation Characterization during In-situ Straining TEM: Benjamin Eftink¹; Stuart Maloy¹; ¹Los Alamos National Laboratory
    Revealing the three-dimensional information of dislocations from TEM experiments using conventional methods requires a large amount of input data acquired with the same diffraction conditions. Combining the three-dimensional spatial characterization with in situ straining TEM experiments is particularly difficult because of maintaining the same diffraction condition with a single tilt axis sample stage. That lack of three-dimensional characterization during deformation leaves out key aspects of the deformation process including dislocation character and slip plane which are both important to how dislocations are predicted to glide, climb and interact with other defects. Using a recently developed stereo-tomography approach, extracting three-dimensional spatial and crystallographic information requires minimal data inputs and can be efficiently combined with in-situ TEM experiments. Only two TEM images, that can be in different diffraction conditions, are needed to create the three-dimensional spatial models. The technique is computationally simple and easily executed with open source software Obtain3D_open.

9:30 AM Break

9:50 AM
In Situ TEM Measurements of Electron-induced Creep in Amorphous Materials: Sourav Das¹; Gowtham Jawaharram¹; Shen Dillon¹; Robert Averback¹; ¹University of Illinois at Urbana-Champaign
    Irradiation-induced creep in amorphous SiO₂, Fe₇₉B₁₆Si₅, Cu₆₀Ta₄₀ and Cu₅₀Ti₅₀ was measured during electron irradiation at room temperature, in situ, in a transmission electron microscope using a miniaturized beam bending apparatus. The TEM was operated using either 80 or 200 kV accelerating voltages, yielding maximum recoil energies below ≈ 15 eV. Molecular dynamics simulations (MD) were performed on amorphous Cu₇₅Zr₂₅ to provide the first detailed damage function for creating flow defects near threshold energies in a metallic glass. The damage function increased with recoil energy approximately as Tⁿ (n ≈ 3-4) between 2 and 10 eV, before becoming linear in energy above ≈ 10 eV. Calculations of the creep rates for Cu₆₀Ta₄₀ and Cu₅₀Ti₅₀ using this model damage function provided good agreement with the experimental creep rates, but they underestimated those for SiO₂ and Fe₇₉B₁₆Si₅. Additional MD simulations of electron beam mixing help to explain these results.

10:10 AM
Deformation and Mechanical Properties of Benzene Microcrystals at Cryogenic Temperatures: Wenxin Zhang¹; Bryce Edwards¹; Lucas Pabarcius¹; Lei Zhong²; Xuan Zhang³; Huajian Gao²; Robert Hodyss⁴; Julia Greer¹; ¹California Institute of Technology; ²Brown University; ³NM—Leibniz Institute for New Materials,; ⁴Jet Propulsion Laboratory
    Small-molecule organic “minerals” (e.g., benzene, naphthalene) are ubiquitous on cold Solar-System bodies, forming topologies on Saturn’s moon Titan. Understanding its geological history is imperative for designing landed missions and requires knowing the mechanical properties and deformation of organic minerals. We perform in-situ nanomechanical experiments on ~10μm-tall pyramidal benzene crystallites, cryogenically formed from liquid droplets in SEM chamber. TEM analysis reveals single-crystalline microstructure, and micro-compression experiments convey top contact pressure to decay from ~2 GPa at initial contact to ~0.5 GPa at ~1-μm compression. Deformation occurred via layer-by-layer densification of benzene unit cells, evidenced by stiffness signature and stochastic displacement bursts. Molecular dynamics simulations unveiled densification to occur via propagation of intermolecular slip followed by amorphization or phase transition. We demonstrate feasibility of cryogenic in-situ nanomechanical characterization of solid organics, providing direct implications to better understanding geophysics of planetary bodies.

10:30 AM
In-situ Mechanics of Superalloys and Bond Coating at 1000C: Sanjit Bhowmick¹; ¹Bruker
    High-strength structural materials such as Ni-based superalloys and diffusion bond coats are widely used in challenging environments with exposure to mechanical fatigue, particle impact, and erosion at elevated temperatures. Diffusion aluminide bond coats are an example of compositionally and microstructurally graded coatings with significant variation in engineered mechanical properties across the cross-section. Nanoindentation and pillar compression, particularly in situ, can be considered as a well-suited technique for measuring the properties of such complex microstructural materials as the deformation volume can be carefully controlled to probe different precipitates and microstructural zones. In this study, an SEM nanomechanical instrument with an integrated high-temperature stage and an active tip heating was used to conduct pillar compression of aluminide bond coating and superalloy substrate at room temperature and up to 1000C.