Heterostructured and Gradient Materials (HGM IV): Tailoring Heterogeneity for Superior Properties: Harmonic Structure, Composites and Films
Sponsored by: TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Yuntian Zhu, City University of Hong Kong; Kei Ameyama, Ritsumeikan University; Irene Beyerlein, University of California, Santa Barbara; Yves Brechet, Grenoble Institute of Technology; Huajian Gao, Nanyang Technological University; Hyoung Seop Kim, Pohang University of Science and Technology; Ke Lu, Institute of Metal Research; Xiaolei Wu, State Institute of Mechanics, Chinese Academy of Sciences
Wednesday 8:30 AM
March 17, 2021
Room: RM 46
Location: TMS2021 Virtual
Session Chair: Kei Ameyama, Ritsumeikan University; Dmytro Orlov, Lund University; Benjamin Guennec, Toyama Prefectural University
8:30 AM
Unique Hall-petch Relation in Harmonic Structure Materials: Kei Ameyama1; 1Ritsumeikan University
The Harmonic Structure (HS) design has been applied to pure metals and alloys via SPD powder metallurgy process. At a macro-scale, the harmonic structure materials exhibited significantly better combination of strength and ductility, as compared to their homogeneous microstructure counterparts. This behavior is essentially related to the ability of the HS to promote a large strain hardening and uniform distribution of strain during plastic deformation, leading to improved mechanical properties by avoiding or delaying localized plastic instability. Moreover, HS materials showed a new extra hardening Hall-Petch relationship behavior in the grain size range larger than several tens microns. This unique phenomenon is considered to be due to strain hardening which started prior to 0.2% strain. Such unique and outstanding mechanical properties of HS materials are attributed to the synergy effects of nano and macro scale structures.
8:50 AM Invited
Size Effect Issue on the Fatigue Properties of Ti-6Al-4V Designed in Heterogeneous Harmonic Structure: Benjamin Guennec1; Takayuki Ishiguri2; Mie Ota Kawabata3; Shoichi Kikuchi4; Akira Ueno3; Kei Ameyama3; 1Toyama Prefectural University; 2Mitsui High-tec; 3Ritsumeikan University; 4Shizuoka University
Lately, heterogeneous tailored microstructures are reported to enhance the mechanical properties of metallic materials toward its homogenous structure counterparts. Consequently, numerous works have been undertaken to analyze the related mechanism, proposing several heterogeneous microstructure patterns. In the present work, four-point bending fatigue properties of Ti-6Al-4V designed in heterogeneous harmonic structure, obtained via powder metallurgy route, are examined using two distinct specimen sizes. Furthermore, the present work also involves fatigue results from homogeneous counterparts for the sake of reference. Experimental results emphasize a clear effect of the specimen size on the fatigue strength of harmonic materials, whereas the homogeneous structure material shows similar strengths for both specimen size configurations. Refine analyses suggest that the specimen size alters the dislocation activity at the interface between coarse and fine grain regions of the harmonic structure, which implies consequences on the strain distribution over such heterogeneous structure.
9:15 AM
Yielding in a Metallic Nanocomposite at the Nanoscale: Kangpyo So1; Myles Stapelberg1; Yu Ren Zhou1; Hideki Mori2; Shigenobu Ogata2; Michael Short1; Ju Li2; Sidney Yip1; 1Massachusetts Institute Of Technology; 2College of Industrial Technology
Yielding is an intriguing phenomenon which has intimate links with plasticity and fracture in materials. Understanding the microscopic nature of yielding allows designing materials with improved performance. Yet, fundamental yielding mechanisms have not been fully understood, especially in nanostructured metal composites. In this work, we propose a yielding mechanism of a nanofiber-filler metal-matrix nanocomposites. We uncover unit processes at the nanoscale during mechanical deformation and rupture of CNT-Al nanocomposite through in-situ TEM coupled with numerical analysis. Non-shearable CNTs provide a strong pinning point on dislocation glide or crossover, triggering high local shear strains which result in shear transformation deformation. Bridging of the notch tip by CNT hinders further penetration of notch, indicating substantial nanoscale load transfer. Further details from atom-scale simulations of CNT-induced hardening along with strain redistribution during deformation will be discussed. Our nanoscale observations and interpretations reveal the mechanistic nature of deformation in a complex, out-of-equilibrium materials system.
9:35 AM Invited
Lattice Defect Development in Harmonic Metals through Atomic Simulations: Tomotsugu Shimokawa1; Tatsuya Hasegawa1; Tomoaki Niiyama1; 1Kanazawa University
Harmonic (core-shell) materials, with a network structure in which coarse-grain regions (core) are surrounded by fine-grain regions (shell), show both higher strength and higher elongation than homogeneous fine grain or coarse grain structured metals. In this study, elucidating the effect of structural heterogeneously on lattice defect developments and on mechanical properties of harmonic materials, we perform tensile loading tests to harmonic metals, of Al or Cu through molecular dynamics simulations. The grain sizes of shell and core regions are 9 nm and 27 nm, respectively. The propagation of plastic deformation via the interface between shell/core regions and the propagation direction is influenced by the existence of intragranular dislocations. This causes the inhomogeneous deformation between shell and core regions. We will show the influence of such inhomogeneous lattice defect development on the mechanical properties of harmonic metals.
10:00 AM Invited
Backstress Development and Strain Partitioning in Harmonic-structure Materials: Dmytro Orlov1; Roman Kulagin2; Yan Beygelzimer3; 1Lund University; 2Karlsruhe Institute of Technology; 3Donetsk Institute for Physics and Engineering
A new class of multifunctional high-performance Heterostructured and Gradient Materials (HGM) have been emerging recently. Harmonic-Structure (HS) materials that can be produced by bottom-up architecting from powder metals, feature bi-modal distribution of grain sizes arranged into a continuous 3D-skeleton from ultrafine-grains (UFG) with coarse-grain (CG) inclusions. They have been proven among top-performing HGMs, but further property optimisation is restricted by the limited understanding of HS mechanics. We recently developed a simple yet powerful analytical model for evaluating backstress development and strain partitioning between CG and UFG components in HS materials. The model captures specifics of topology in HS under mechanical loading allowing quantitative analysis of critical parameters from simple calibration experiments. The analysis of experimental data from HS nickel reveals favourable strain partitioning between CG / UFG along with the build-up of back-stress on their interfaces allowing the material performance to exceed expectations from the rule of mixtures.
10:25 AM Invited
Outstanding Mechanical Properties in a Harmonic Structure Designed Titanium Due to Preferential Recrystallization: Bhupendra Sharma1; Motoki Miyakoshi1; Mie Kawabata1; Kei Ameyama1; 1Ritsumeikan University
The effect of thermomechanical processing (TMP), consisting of cold rolling followed by annealing, on the microstructure and mechanical properties of three-dimensional hetero-structured Harmonic Structure designed pure Ti (HS-Ti) was studied. The TMP revealed the occurrence of preferential dislocation accumulation in the Shell as well as Shell-Core interface areas during plastic deformation, i.e. cold rolling, leading to the evolution of peculiar preferentially recrystallized structure localized in the Shell and Shell-Core interface regions of the HS-Ti compacts. The underlying mechanism for such a unique microstructural evolution in the TMP HS-Ti has been discussed and proposed. It has been demonstrated that it is feasible to manipulate the microstructure of Core/Shell via control-ling TMP parameters. It has been demonstrated that the peculiar phenomenon of preferential recrystallization in the predetermined Shell and Shell/Core interface could be a viable method in achieving precise control over microstructure and mechanical properties.
10:50 AM
High Strength and Tensile Ductility in Bicrystalline Nickel Thin Films with Incoherent Twin Boundaries: Rohit Berlia1; Jagannathan Rajagopalan; 1Arizona State University
Freestanding metallic films typically show high strength but low strain hardening capacity, which leads to low failure strains (< 5%). Here, we report the mechanical behavior of bicrystalline Ni films that exhibit high strength and significant ductility. Ni films (200 nm - 2.5 μm thick) were deposited on Si (111) substrates with a 25 nm Ag buffer layer at room temperature using magnetron sputtering. TEM and EBSD characterization revealed that the films are composed of two (111) grain variants with an incoherent twin boundary at their interface. Freestanding samples of the films were co-fabricated with MEMS tensile stages and their uniaxial stress – strain response was measured at quasi-static strain rates. The experiments revealed flow stresses approaching 1 GPa and significant strain hardening, which resulted in uniform elongation >10% in the thickest films. Possible mechanisms for the high strength and relatively large ductility in these films will be discussed.
11:10 AM
Effect of Rolling on Fatigue Crack Propagation in Harmonic Structured Commercially Pure Titanium: Yoshikazu Nakai1; Shoichi Kikuchi2; Kohei Osaki1; Mie Kawabata3; Kei Ameyama3; 1Kobe Univ; 2Shizuoka University; 3Ritsumeikan University
Commercially pure (CP) titanium with a bimodal harmonic structure, which is defined as coarse-grained structure surrounded by a network structure of fine grains, was fabricated by consolidating mechanically milled powders to improve both the strength and ductility. In the present study, thermo-mechanical processing (TMP) was performed for the CP titanium with a bimodal harmonic structure to improve its fatigue properties. Fatigue crack propagation tests were conducted to clarify the effects of rolling ratio, rolling direction, and force ratio of TMP-treated CP titanium with harmonic structure. For either material, the crack growth rates for L-T direction were always higher than that of T-L direction, and the rate for higher force ratio is higher for higher force ratio and higher rolling ratio, where the crack growth direction was perpendicular to the rolling direction for L-T direction, and it was parallel to the rolling direction for T-L direction.
11:30 AM
Synthesis and Mechanical Characterization of Metallic Films with Precisely Defined Heterogeneous Microstructures: Rohit Berlia1; Jagannathan Rajagopalan; 1Arizona State University
Materials with heterogeneous microstructures exhibit a superior combination of strength and ductility, but our ability to synthesize such materials with rigorously microstructural control is still limited. Here we report a novel technique to synthesize metallic films with precisely defined bimodal microstructures, wherein the size, volume fraction and connectivity of nanocrystalline (NC) and single crystal (SC) domains can be explicitly controlled. Using this technique, we synthesized iron films in which NC and SC domains were configured in series and parallel arrangements, and explored their stress-strain behavior. As anticipated, films with parallel arrangement exhibited higher strength due to co-deformation of NC and SC domains. More interestingly, the orientation of SC domains with respect to the loading axis significantly influenced the stress-strain response due to the constraints it imposed on dislocation motion. This synthesis method provides a route to systematically tailor the mechanical behavior of metallic films in a highly reproducible manner.