Multiscale Architectured Materials (MAM II): Tailoring Mechanical Incompatibility for Superior Properties: Heterogeneous Materials
Sponsored by: TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Yuntian Zhu, North Carolina State University; Irene Beyerlein, University of California, Santa Barbara; Yves Brechet, Grenoble Institute of Technology; Huajian Gao, Brown University; Ke Lu, Institute of Metal Research, Chinese Academy of Science; Xiaolei Wu, Institute of Mechanics, Chinese Academy of Science

Monday 2:00 PM
February 27, 2017
Room: 24B
Location: San Diego Convention Ctr

Session Chair: Yuntian Zhu, NC State University; Kei Ameyama, Ritsumeikan University

2:00 PM  Invited
Unique Deformation Behavior of Harmonic Structure Materials with High Strength and High Ductility: Kei Ameyama1; Mie Ota1; 1Ritsumeikan University
    The harmonic structure has a heterogeneous microstructure consisting of bimodal grain size together with a controlled and specific topological distribution of fine and coarse grains. In other words, the harmonic structure is heterogeneous on micro- but homogeneous on macro-scales. In the present work, the harmonic structure design has been applied to pure-Ti, Ni, Cu, Fe, Ti-6Al-4V alloy and SUS304L stainless steel via a powder metallurgy route consisting of controlled severe plastic deformation of the corresponding powder via mechanical milling or high pressure gas milling, and subsequent consolidation by SPS. At a macro-scale, the harmonic structure materials exhibited significantly better combination of strength and ductility, under quasi-static loadings, as compared to their homogeneous microstructure counterparts. This behavior was essentially related to the ability of the harmonic structure to promote the uniform distribution of strain during plastic deformation, leading to improved mechanical properties by avoiding or delaying localized plastic instability.

2:25 PM  
Deformation Mechanisms in Multiscale Architectured Harmonic-structured Nickel: Dmytro Orlov1; Stephen Hall1; Jinming Zhou1; Mie Ota2; Kei Ameyama2; 1Lund University; 2Ritsumeikan University
    Traditional materials having homogeneous coarse or ultrafine-grained structures can hardly meet increasingly stringent demands for high-performance applications due to inversely correlated strength-ductility relationship. The emerging fabrication of heterogeneous structures architectured at multiple scales promises a breakthrough. Of particular interest are harmonic-structured (HS) materials featuring islands of coarse grains embedded into a continuous 3D skeleton of their ultrafine-grained counterparts. In the present work, nickel samples with bimodal-harmonic and bimodal-random structures were fabricated by wet milling followed by spark plasma sintering. Mechanical tests, in-situ and post-mortem observations of microstructure, digital image correlation analysis and Finite-Element simulations allowed elucidating the roles of ultrafine-grain fractions and grain distribution topology in the mechanical performance of HS Ni. Both bimodal structures demonstrate excellent combination of strength and elongation, while HS arrangement promotes the homogenization of strain distribution thus further delaying strain localization. The details of mechanisms governing such behavior will be discussed.

2:45 PM  Invited
Atomistic and Mesoscale Modeling Investigation of Deformation Mechanisms in Heterogeneous Materials: Shenyang Hu1; 1Pacific Northwest National Laboratory
    Experiments show that a heterogeneous structure such as bimodal and gradient structures could improve both materials strength and ductility. However, it is not well understood what are the synergy mechanisms of deformation in such a heterogeneous microstructure and what kind microstructures have optimal strength and ductility. This talk will present atomistic and mesoscale modeling capability for studying the effect of heterogeneous microstructures on deformation mechanisms and mechanical properties. A phase-field model of crystal plasticity was developed to investigate the non-uniform deformation response and deformation-induced recrystallization in polycrystalline structures. Molecular dynamics method is employed to explore the deformation mechanisms in nano-crystalline structures. The bimodal Cu and/or Fe crystals are taken as model structures. The effect of the microstructures on elastic-plastic deformation is investigated. Both atomistic and mesoscale simulation results reveal that microstructures with a soft phase embedded in a hard phase matrix can improve both materials strength and ductility.

3:10 PM  Invited
Tensile Properties of Heterogeneous Structures Embedded with Nanotwins: Nairong Tao1; F.K. Yan1; H.Y. Yi1; Y. Zhang1; Y.S. Li1; 1Shenyang National Laboratoty for Materilas Science, Institute of Metal Research, Chinese Academy of Sciences
    Recently, a novel strategy was proposed for strengthening metallic materials by introducing nanotwins. In our work, heterogeneous structures embedded with nanotwins were prepared in various metals including copper and steels by using dynamic plastic deformation and subsequent annealing. The deformation nanotwins with a reduced dislocation density exhibit a high strength and a certain ductility, which makes heterogeneous metals have a high strength and a good ductility. Deformation mechanisms of nanotwins, including interactions of dislocations with twin boundaries, generation of stacking faults and strain-induced martensitic transformation, depend on stacking fault energies and material natures. The occurrence of stacking faults and strain-induced martensitic transformation constrains dynamic recovery of dislocations and deformation localization, thereby contributing significantly to the work hardening and ductility. Our results showed that tailoring heterogeneous microstructures is a potential approach to raise strength and keep good ductility.

3:35 PM Break

3:55 PM  Invited
Investigation of Effects of Microstructural Heterogeneity on Mechanical Properties Using Samples Prepared by Park Plasma Sintering: Andy Godfrey1; Kainan Zhu1; Chenglu Zhang1; 1Tsinghua University
    By control of the sintering conditions and powder characteristics is it possible to prepare microstructures in a fully recrystallized state with controlled grain size using spark plasma sintering. This has been used to investigate the effect of heterogeneity in grain size by mixing of powders with different average sizes. In one experiment aluminum powders with 1 μm and 6 μm average particle sizes were mixed with different weight fractions and tensile tests used to explore the relationship between mechanical strength ductility as a function of microstructural heterogeneity. In a separate experiment powders of copper and steel have been mixed to prepare a dual-phase microstructure in which the volume fraction, average size, and strength of each phase can be varied independently over a large range.

4:20 PM  Invited
Taming Microstructure of Nanostructured Alloy through the Concurrence of Phase Transition and Grain Growth: Feng Liu1; 1Northwestern Polytechnical University
    In nanostructured metals, heterogeneous and hierarchical microstructures have yielded great success in improving the low ductility, which has been the Achilles heel of their application as structural materials. To achieve such microstructures, generally, current strategies focus on the design of fabrication processes rather than the application of inherently microstructural changes such as phase transition and grain growth, since they are conventionally believed as two undesirable reactions when nanostructured materials suffer instability. Here, we report a solid-reaction based technique arising from the concurrence of phase transition and grain growth, achieving a new kind of heterogeneous microstructure, i.e. dual-phase bimodal nanostructure. The physics behind the concurrence aiming to understand the dual-phase bimodal nanostructure is elucidated. The present finding, offers a feasible strategy taming, instead of inflexibly retaining, the nanostructure, which may further serve as a new guideline for alloying in designing nanostructured alloys with optimized mechanical properties and good thermal stability.

4:45 PM  Invited
Tuning Heterogeneity in Metals for Better Hardenability and Deformability: Examples from TWIP Steels and High Entropy Alloys: Yujie Wei1; 1LNM, Institute of Mechanics, CAS
    Microstructure heterogenization is broadly employed to enhance the strength and ductility of materials. Typical routines include realizing bi-modal grain size distribution in polycrystalline metals, making multi-phase alloys such as dual-phase steels, adding dispersed crystalline phase in monolithic metallic glasses, and so on. Recently, the combination of heterogeneous microstructures with gradient shows a synergetic effect in realizing better strength and ductility. In this talk, we will discuss how heterogeneous microstructures could be realized in engineering level structures. We take the twin-induced plasticity steel and high entropy alloys as model cases, and show the enhanced mechanical properties due to the presence of heterogeneous structures at micro to nanoscale. We also discuss the physical origin which leads to the superb hardenability and deformability in those materials.

5:10 PM  
Heterogeneous Structures: A New Paradigm for Designing Super Strong and Tough Materials: Xiaolei Wu1; Yuntian Zhu2; 1Institute of Mechanics, Chinese Academy of Sciences; 2North Carolina State University
    Recently, heterogeneous structure is found to produce unprecedented strength and ductility that are considered impossible from our textbook knowledge and materials history. In addition, it also exhibits other unusual mechanical behaviors such as very high strain hardening rate. It is suggested that mechanical incompatibility between heterogeneous domains is primarily responsible for the observed phenomenon. This represents a new paradigm for designing strong and tough structural materials. Heterogeneous materials have recently attracted extensive attention in the academic community and are emerging as a hot research field. Importantly, heterogeneous materials can be produced by currently available industrial facilities at low cost, and has the potential to revolutionize the manufacturing industry by providing strong materials for energy efficient transportation vehicles and other applications. In this talk we will present and discuss the perspective, prospects, and problems of heterogeneous materials.