Mechanical Behavior at the Nanoscale V: Microstructure Effects
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Mechanical Behavior of Materials Committee, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Christopher Weinberger, Colorado State University; Megan Cordill, Erich Schmid Institute of Materials Science; Garritt Tucker, Colorado School of Mines; Wendy Gu, Stanford University; Scott Mao; Yu Zou, University of Toronto
Monday 8:00 AM
February 24, 2020
Room: Santa Rosa
Location: Marriott Marquis Hotel
Session Chair: Garritt Tucker, Colorado School of Mines; Chuang Deng, University of Manitoba
8:00 AM
Improved Strength and Toughness in Metal-MAX Nanolaminates Through Nanoscale Mechanistic Competition: Jacob Gruber1; Siddhartha Pathak2; Garritt Tucker1; 1Colorado School of Mines; 2University of Nevada, Reno
Metal-MAX nanolaminates with layer thickness below 50nm are hierarchical, multi-layered nanocomposite materials that exhibit tunable strength and toughness, under both compressive and tensile stresses. Layering both between metal and MAX layers, as well as within the MAX phase itself give rise to unique mechanical behavior. Using atomistic simulation, the deformation of nanolaminates in a variety of configurations mirrors the behavior observed in experiment. Increased strength and toughness are observed, especially in specific orientations, and orientation also determines the failure mode, whether kinking, in-plane dislocation plasticity or interfacial sliding. Leveraging kinematic metrics at the atomic scale, we identify that these transitions arise from the competition of atomic deformation mechanisms, whose activation depends on orientation. Modulation of layer thickness allows for the competition to be tuned. This tunability has the potential for use in high-temperature structural applications, leveraging the unique mechanical properties of the composite as well as it’s thermal stability.
8:20 AM
Micromechanical Studies of Laser Surface Remelted Hypereutectic Al-20Si Alloy: Huai-Hsun Lien1; Amit Misra1; Jyoti Mazumder1; 1University of Michigan
Heterogeneous metallic materials with multimodal grain size distribution of constituent grains and phases show significant improvements in ductility at yield strength comparable to their nanocrystalline counterparts. In this report, model system heterogeneous hypereutectic Al-20Si with μm-size coarse Al dendrites embedded in nm-size ultrafine Al-Si eutectic was fabricated by laser surface remelting (LSR). The mechanical properties of both the heterogeneous Al-Si structure and fully ultrafine eutectic was studied. Hardness testing and micropillar compression reveal different mechanical properties for as-cast Al-12Si eutectic, heterogeneous structure and fully ultrafine eutect. In addition, the hardness increases as the fraction of ultrafine Al-Si eutectic increase. in-situ SEM and in-situ TEM further reveal the deformation behaviors of micropillars and nanopillars. These findings are crucial to constructing the microstructure to mechanical property map for future guidance.
8:40 AM
Stability of Nanotwinned Thin Metal Films: Shefford Baker1; Nathaniel Rogers1; Kenneth Shaughnessy1; 1Cornell University
High densities of twin boundaries parallel to close-packed directions in thin FCC and HCP films made using atom-by-atom deposition processes are of interest because of the potential to create materials with high strength and high ductility. However, to achieve these properties, such structures must be stable. Twin boundaries represent additional stored energy and can in principle assist in driving grain growth. We have developed methods to systematically vary the density of these defects during film deposition and show that the kinetics of grain growth are consistent with the expected nanotwin densities. Only under certain conditions are the microstructures stable. We discuss the magnitudes of the driving forces as well as strategies for stabilizing these structures.
9:00 AM Invited
Atomistic Simulation of Twinning Mediated Deformation and Plasticity in Au Nanowires: Chuang Deng1; Frederic Sansoz2; Reza Rezaei3; 1University of Manitoba; 2University of Vermont; 3University of Tehran
Twinning plays important roles during the deformation of FCC metal nanowires, especially those with low stacking fault energy such as Au. Thanks to the rapid development of in-situ nanomechanical testing platform in recent years, it is now a common practice to directly compare experimentally observed deformation behavior in nanoscale materials with atomistic simulations. In this talk, the roles of both pre-existing coherent twin boundaries and deformation twinning on the strength and plasticity in Au nanowires as explored by atomistic simulations will be presented and compared with those reported experimentally based on in-situ nanomechanical tests. The specific topics include the size dependent strength and plasticity in Au nanowires with equi-spaced horizontal twin boundaries, a new form of pseudo-elasticity in Au nanowires with slanted twin boundaries, and shape-memory effects in single crystalline cylindrical Au nanowires mediated by deformation twinning.
9:40 AM Break
10:00 AM
Mechanical Phase Mapping of Meteorites: Combining EDX and Nanoindentation: Jeff Wheeler1; 1ETH Zurich
Meteorites are perhaps one of the most tangible aspects of outer space. The internal microstructure and composition of meteorites has been intensively studied and classified by astro- and geo-chemists to study their origins and formation processes. However, other than some microhardness testing in the 1950s, very little has been done to characterize their mechanical behavior. With the advent of modern, high speed nanoindentation techniques, it is now possible to map the mechanical features of materials over square millimeters of area with micron-level resolution in a reasonable amount of time. Using statistical analysis, the properties of each of these phases can be extracted. By combining this information with EDX maps, the relationship between composition and properties of the various phases can be quantified. In this work, high speed nanoindentation is combined with energy-dispersive X-ray spectroscopy (EDX) to map the mechanical properties of a variety of different nickel-iron meteorites.
10:20 AM
Role of Grain Boundaries on Plasticity and Fracture of Nanocrystalline MgAl₂O₄: Jessica Maita1; Jacob Davis2; James Wollmershauser3; Edward Gorzkowski3; Boris Feigelson3; Seok-Woo Lee1; 1University of Connecticut; 2University of Massachusetts Amherst; 3U.S. Naval Research Laboratory
Transparent materials are used extensively due to their ability to transmit light and provide physical protection from external chemical and mechanical interactions. Transparent nanocrystalline MgAl₂O₄ has been developed with grain sizes ranging 3.7 to 80 nm, the smallest reported. Both nanoindentation and uni-axial micromechanical tests are performed to elucidate the role of high grain boundary density on plasticity and fracture. For nanoindentation, the Hall-Petch (H-P) relation is observed up to 10.5 nm grain size, beyond which an inverse H-P relation is observed. However, microcompression results show that fracture strength keeps increasing as the grain size decreases without inverse H-P relation. HRTEM revealed the presence of amorphous grain boundaries, which play different roles; as fracture initiators in uniaxial compression and plasticity barriers/carriers in nanoindentation. These results provide a better understanding of the mechanical behavior and help improve the design of transparent armor with superior protection capability.
10:40 AM
Deformation Mechanisms in a Nanocrystalline CuTa Alloys under Shock Loading Conditions: Billy Hornbuckle1; Steven Dean1; Xuyang Zhou2; Anit Giri1; Anthony Roberts1; Greg Thompson2; Kris Darling1; 1US Army Research Laboratory; 2University of Alabama
The deformation mechanisms truly governing nanocrystalline materials are still a bit of a mystery with regard to a thermally and mechanically stable nanocrystalline alloy. This work looks to report on the deformation mechanisms in a Cu-3Ta (At.%) alloy that has undergone shock loading via laser-driven flyer plate experiments. The highest plate velocity of 2.4 km/sec generates a 34 GPa pressure wave through the alloy. Post mortem transmission electron microscopy (TEM) is performed on a sample extracted from the impact crater using a focused ion beam (FIB) to note changes in grain size, dislocation density, and possible twin formation. Precession electron diffraction (PED) is also performed to quantify any change in texture evolution of the specimen after experiencing these elevated stress state.
11:00 AM Cancelled
Thermally Stable and High-strength Nanoporous Aluminum: Wei Yang1; Hai-Jun Jin1; 1Institute of Metal Research, CAS
Nanoporous metals exhibit high strengths because of a “smaller is stronger” effect in their nanoscale ligaments. Most previous studies have been performed on nanoporous (np) gold, which is unsuitable for structural applications and is unstable against coarsening at even room temperature. On the other hand, porous Al has been widely used in many applications. But only very recently, it becomes possible to introduce np structure into Al, by combining galvanic replacement reaction and dealloying (W. Yang et al, J. Electrochem. Soc. 2018). The naturally occurred surface oxide prevents surface diffusion, leading to a high thermal stability of np Al at temperatures even close to its melting point. Mechanical tests show that these np Al samples are stronger than fully-dense Al (annealed state), under compression and tension, because of the small ligament diameter, small grain size and the presence of a thin surface oxide layer. Their roles in deformation will be discussed.