Session Chair: In-Suk Choi, Korea Institute of Science & Technology Session Chair: Guang-Ping Zhang, Institute of Metal Research, Chinese Academy of Sciences
10:30am - 11:00am Invited
Plastic Deformation Instability of Metallic Nanolayered Composites
Institute of Metal Research, Chinese Academy of Sciences, China
Metallic nanolayered composites made of two alternating metal layers with different interface structures and/or moduli can have strength up to about 1/3–1/2 of the theoretical strength as the individual layer thickness of the composites decreases from the micrometer scale to the nanometer scale. However, at such extreme length scales, plastic deformation of the nanolayered composites usually becomes unstable, as characterized by shear banding accompanied by interface instability through a complex interaction between defects and interfaces. In this talk, we will present experimental and theoretical investigations of plastic deformation behavior and its instability of typical fcc/fcc nanolayered composites, emphasizing variation of interface structure and the interface instability. Plastic deformation instability of the nanocomposites exhibits different features associated with different mechanisms of the interaction of dislocations and interfaces. As the nanolayers were deformed severely to the extreme length scales, the constituent layer thinning and the heterogeneous layer interface also become unstable, leading to further plasticity instability assisted by the shear stress. A detailed analysis for plastic deformation process and the interface effect will be given. It is expected that the findings may provide a basic understanding of the plastic deformation mechanism and plasticity instability of the metallic nanolayered composites at nanoscales.
11:00am - 11:30am Invited
Ultrahigh Tensile Strength Nanowire with Multilayer Ni/Ni-Au Structure
Korea Institute of Science & Technology, South Korea
Introducing nanolayered structures have attracted great interest recently to effectively control the size effect of nanostructured metallic materials. However, previously fabricated multilayer metallic nanostructures have high strength under compressive load but never reached such high strength under tensile loads. Here, we report that our microalloying-based electrodeposition method creates a strong and stable Ni/Ni−Au multilayer nanocrystalline structure by incorporating Au atoms that makes nickel nanowires (NWs) strongest ever under tensile loads. The 3D atomic probe microscopy analysis reveals that secondary alloy elements Au are incorporated into Ni matrix making a graded composition profile across the interface. When the layer thickness is reduced to 10 nm, the tensile strength reaches the unprecedentedly high 7.4 GPa, approximately 10 times that of metal NWs with similar diameters, and exceeding that of most metal nanostructures previously reported at any scale.
11:30am - 11:45am Oral
Enhanced Fracture Toughness in Nanoscale FCC-BCC Multilayered Composite Materials through Interface Engineering
Singapore University of Technology and Design, Singapore
In situ microfracture testing inside an SEM (Scanning Electron Microscopy) with the use of the PI-85 (Hysitron Inc.) picoindenter was conducted with microscale beams of Al-Nb and Cu-Nb nanolayers loaded in the manner of the three-point bending test with fixed ends. Video capture was done to observe the crack behaviour while the experiment was performed. Al-Nb nanolayers exhibited little or no presence of crack hindrance mechanisms with the crack initiated at the notch propagating straight throughout the beam, while Cu-Nb nanolayers showed significant difference in deformation mechanisms leading to the final catastrophic event of failure. Such insights would not have been obtained in an ex situ experiments. Overall, the Cu-Nb nanolayers exhibits enhanced fracture toughness over Al-Nb nanolayers. Our in situ study provided unique insights on the microstructural origins of this crack propagation behaviour and the enhanced fracture toughness. This knowledge could thus lead to enhanced fracture limits in nanomaterials design through interface engineering and hence open up design space for the use of advanced nanomaterials in general in real world systems.
11:45am - 12:00pm Oral
Mechanical Properties of Al 5052 Alloy Processed through Cryogenic Groove Rolling
Yogesha K K1, Amit JOSHI1, Raviraj VERMA1, Jayaganthan R2
1Indian Institute of Technology Roorkee, India; 2Indian Institute of Technology Madras, India
In the present work 5052 Al alloy was subjected to cryo groove rolling followed by post annealing treatment in order to investigate its effect on mechanical properties. The solution treated Al alloys were groove rolled at cryogenic temperature to different true strains. The 90% thickness reduced cryo groove rolled samples exhibit significant improvement in strength (315 MPa) and hardness (122 Hv). It is due to effective suppression of dynamic recovery at cryogenic temperature. Post annealing of the deformed samples was carried out to study its influence on ductility as well as fracture toughness. The post annealed samples exhibits better fracture toughness (206 kJ/m2) due to the formation of bimodal structure consisting of coarse grain (size around 0.5 µm) and ultrafine grain (size around 200 nm). The microstructure of the deformed and post-annealed samples was characterized by optical microscopy, X-ray diffraction, SEM fractography and TEM to understand the tensile and fracture characteristics of the alloy.