Multiscale Architectured Materials (MAM II): Tailoring Mechanical Incompatibility for Superior Properties: Novel and Complex Materials I
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

Wednesday 2:00 PM
March 1, 2017
Room: 24B
Location: San Diego Convention Ctr

Session Chair: Xavier Sauvage, Normandy University; Mingxin Huang, The University of Hong Kong

2:00 PM  
Engineering the Ductile Crack Path by Controlling the Microstructure: Ankit Srivastava1; Shmuel Osovski2; Alan Needleman1; 1Texas A&M University; 2Technion-Israel Institute of Technology
    Ductile fracture limits the performance, safety, reliability and manufacturability of a variety of engineering components and structures; for example, crash worthiness of automobiles, integrity of pipelines, blast resistance of ships and airplane cargo holds, and manufacturability of sheet metal components. The mechanism of ductile fracture in engineering metals and alloys involves nucleation, growth and coalescence of micron scale voids. The aim of this work is to isolate the key features of controlled distributions of void nucleating particles in a material and quantify its effects on crack path and crack growth resistance. Here, finite element, finite deformation calculations are carried out using a constitutive framework for progressively cavitating ductile solids. The material is modeled as an isotropic hardening viscoplastic solid with three dimensional controlled distributions of void nucleating particles. Our results indicate that by controlling the particle distribution we can control the crack path and maximize the crack growth resistance.

2:20 PM  
Improved Balance of Mechanical Properties in Cryomilled Al-Mg Alloy Through Thermomechanical Processing: Holden Hyer1; Clara Hofmeister2; Yongho Sohn2; Bhaskar Majumdar1; 1New Mexico Tech; 2University of Central Florida
    It has been demonstrated in the past that Al-Mg alloys that have been cryomilled in liquid nitrogen exhibit extremely high strength in compression, typically 900-1000 MPa. The nanosize grains and the high nitrogen content (0.5 to 1.5 wt.%) contribute to this behavior. However, elongation to failure is almost zero. In this work we have used slow strain-rate extrusion over a range of temperatures to modify the microstructure, and have demonstrated tensile strength in excess of 725 MPa and elongations ranging from 2 to 5%. It is shown that this attractive balance of tensile properties is obtained through a multiscale microstructure, ranging from 50 nm to 2 micrometers. The mechanical incompatibilities associated with these very different grain size is likely responsible for the good balance of properties. The microstructures and mechanisms will be discussed.

2:40 PM  
Stabilization of Nanocrystalline Fe-Zr Alloys by Nanoscale Zr-rich Clusters: Yuzeng Chen1; 1Northwestern Polytechnical University
    Nanocrystalline Fe-Zr alloys exhibit extraordinary thermal stability to resist grain coarsening at elevated temperatures, which enables their potential applications in various fields. It has been suggested the stabilization of nanoscale grain size of these alloys is ascribed to the reduction in grain boundary energy by Zr segregation in grain boundaries at modest temperatures and Zener pinning of Fe3Zr precipitates at high temperatures. Our new results obtained by a combined investigation of high-resolution X-ray diffraction, transmission electron microscopy, and atom probe tomography indicate that below the temperatures for formation of Fe3Zr precipitates, Zr atoms do no show a strong segregation in grain boundaries; instead, highly dispersed Zr-rich clusters having a similar structure to the matrix bcc phase may probably play an dominant role in stabilizing the nanoscale grain size. The underlying stabilization mechanism of these clusters on the grain size is under investigations.

3:00 PM  
Improving Composite Ductility through Corrugated Reinforcement Architecture: Mark Fraser1; Hatem Zurob1; Peidong Wu1; 1McMaster University
    Architectured materials can be optimized to achieve desirable property combinations by controlling the geometry of the reinforcement and the contrast between phases. Of particular interest is the corrugation reinforced composite, due to its combination of high ductility and strength. Unbending of the corrugated reinforcement during loading leads to additional ductility while also strengthening the composite through the evolution of the reinforcing geometry. While the isolated corrugation geometry has been investigated in detail for sandwich style hybrid materials, its application as a reinforcement embedded in a matrix has been minimally explored. This presentation explores the corrugated architecture in metal matrix composites, investigating the effect of geometric parameters of the corrugation and material properties of the components on the overall ductility improvement compared to a straight reinforcement. Using Finite Element Modeling (FEM) and experimental techniques, including casting and subsequent deformation, it is seen that there is interplay between geometry and material properties.

3:20 PM Break

3:35 PM  Invited
Ultra-strong and Ductile Nanotwinned Steel: Peng Zhou1; Rendong Liu2; Xu Wang2; M.X. Huang1; 1The University of Hong Kong; 2Ansteel Group
    An ultra-strong and ductile nanotwinned steel was fabricated by a simple thermomechanical treatment consisting of cold rolling and recovery annealing. Different to other lab-scale methods making nano-structured materials, the present simple thermomechnical treatment is suitable for large-scale production in the steel industry using existing facilities, which makes the present steel being an attractive structure material. The nanotwinned steel achieved a high yield strength (1450 MPa), high ultimate tensile strength (1600 MPa) and considerable uniform tensile elongation (20%). The average twin thickness and spacing are 5 nm and 40 nm, respectively. The deformation mechanism of the present nanotwinned steel is investigated by synchrotron X-ray diffraction, transmission electron microscopy, nanoindentation and electrical resistivity, illustrating that the dislocation density increases dramatically with strain while the volume fraction of nanotwins remains constant. A physically-based model is proposed to simulate the evolution of dislocation density and stress-strain relation, showing good agreement with the experimental results.

4:00 PM  
Multi Scale Modeling of Mechanical Behavior of Covalently Cross-linked SWCNT Aerogels: Ankit Gupta1; Andy Jiang1; Elizabeth Holm1; 1Carnegie Mellon University
    Single Wall Carbon Nanotubes (SWCNT) form random networks in aerogels that are governed by the van der Waals interaction at nodes. These aerogels show high initial stiffness as compared to other classes of aerogels. However, they tend to deform in a plastic manner for strains>9%. Recently there have been some experimental studies showing that nanotubes in these aerogels can be covalently cross-linked. The cross-linking is supposed to improve stiffness as well as the yield strength of these materials. In this study, we model mechanical behavior of such aerogels using a multi-scale modeling approach. The model uses Molecular Dynamics (MD) simulations to model polymer cross-links between nanotubes and a Finite Element Model (FEM) to study the mechanical behavior of such networks at continuum scale.

4:20 PM  Invited
Multiscale and Multiphase Structures Obtained by Large Deformation Processes to Achieve Unique Properties Combinations: Xavier Sauvage1; 1Normandy University
    The application of large deformation processes to achieve multiscale and multiphase or composite structures will be discussed in this presentation. The basic concept of drawn in-situ composites, like Cu-V wires, will be extended to introduce the accumulated drawing process. The design of specific architectures will be illustrated by the Fe-Mg system that has been investigated to try to achieve high strength, high ductility and low weight structures. Finally, the application of alternative processes involving severe plastic deformations like high pressure torsion or equal channel angular pressing for the design of architectured materials will be also discussed and illustrated with materials prepared from powder mixtures.

4:45 PM  
Designing Optimal Bimodality in Harmonic Architectured Materials Using Statistical Synthetic Model: Hyung Keun Park1; Jaimyun Jung1; Hyoung Seop Kim1; 1Pohang University of Science and Technology
     In recent years, metallic materials with a bimodal distribution of grain size have received a lot of interest due to their ideal combination of high strength and reasonable ductility. As a new architecture, harmonic structure, which is composed of periodically arranged coarse-grained cores and ultrafine-grained shells, can be regarded as a kind of bimodal structures. In this presentation, we investigate the relationship among strength, ductility, and bimodality of grain sizes, and propose an optimal harmonic architectured structure. Virtual three-dimensional harmonic structures with various bimodalities are synthesized using a statistical model. The finite element method is employed to evaluate the mechanical properties of the synthesized harmonic structures. The remarkable winning combination of strength and ductility was achieved at certain bimodality, compared to their coarse-grained and ultrafine-grained structures.