Ultrafine-grained and Heterostructured Materials (UFGH XI): Processing, Microstructure & Property
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Caizhi Zhou, University of South Carolina; Megumi Kawasaki, Oregon State University; Enrique Lavernia, University of California, Irvine; Terry Lowe, Colorado School of Mines; Suveen Mathaudhu, Colorado School of Mines; Ruslan Valiev, UFA State Aviation Technical University; Yuntian Zhu, City University of Hong Kong
Wednesday 8:30 AM
February 26, 2020
Room: Carlsbad
Location: Marriott Marquis Hotel
Session Chair: Xiuyan Li, Institute of Metal Research, Chinese Academy of Sciences; Timothy Rupert, University of California, Irvine; Kenneth Vecchio, University of California, San Diego; Boris Straumal, MPI Intelligent Systems
8:30 AM
Mechanical Properties Optimization via Microstructural Control of a Metastable β-type Ti-Nb Gum Metal: Sumin Shin1; Kenneth Vecchio1; 1University of California, San Diego
Microstructure design approaches, leading to twinning-induced plasticity effect through twinned structures and hetero-deformation induced hardening associated with heterogeneous structure (HS), are investigated in this study to tune deformation behavior and correlated mechanical properties in Gum Metal (Ti-23Nb-0.7Ta-2Zr-1.3O at%). The pre-twinned Gum Metal exhibits a pronounced improvement in uniform elongation and work hardening rate, but a lower yield strength with increasing a twin fraction in the microstructure. The experimental results demonstrate that intentional introduced twins are strongly related to the overall softening behavior, and enhanced uniform ductility, attributed to well-distributed twins based on the ‘composite effect’. An intentional heterogeneous structure was accompanied by controlling fraction coarse/fine domains, a spatial grain-size distribution and different types of grain boundaries. The large microstructural heterogeneity leads to obvious mechanical incompatibility and strain partitioning, which, additionally, contributes to induced back-stress hardening and promotes strain delocalization, thereby achieving an exceptional strength-ductility synergy in this Ti-Nb Gum Metal.
8:50 AM
SPD-induced Synthesis of Archimats: a New Paradigm in Materials Design: Roman Kulagin1; Yan Beygelzimer2; Yuri Estrin3; Brigitte Baretzky1; 1Karlsruhe Institute of Technology (KIT) Institute of Nanotechnology (INT); 2Donetsk Institute for Physics and Engineering; 3Monash University / The University of Western Australia
One of the most efficient ways of producing ultrafine-grained materials involves severe plastic deformation (SPD) which breaks down the grain structure to sub-micron or even nano scale. By the very nature of these processes, the materials produced are heterogeneous, at least to some degree. A nascent approach to process design aims at deliberately inducing pronounced heterostructures of various kinds, including multimodal grain populations, gradient structures, harmonic structures, etc. In our work, we put the focus on producing specific structural and compositional patterns, which by preconceived design give rise to improved properties and extend the functionalities of materials architectured by SPD. In the present talk we shall outline the guiding principles behind such SPD-induced synthesis of architectured materials (archimats) and give examples of applications of this approach. The use of Artificial Intelligence and Machine Learning techniques in design of archimats will also be discussed.
9:10 AM
Strain Partitioning by Recurrent Shear Localization during Equal-channel Angular Pressing: Philipp Frint1; Martin Wagner1; 1Institute of Materials Science and Engineering, Technische Universität Chemnitz
We report on recurrent shear localization by formation of alternating shear and matrix bands during ECAP of AA6060. The strain partitioning process is documented by analyzing the deformation of a grid of indents and the corresponding flow lines. Interestingly, shear strains of ~3.6 in the shear bands considerably exceed the maximum shear strain achievable in a single ECAP pass, whereas much lower strains occur in the matrix bands. EBSD analyses document the different stages of microstructural evolution in shear and matrix bands and confirm the pronounced differences associated with the novel strain partitioning process. An analysis of texture evolution for billets with different orientations with respect to the initial extrusion direction demonstrates the importance that texture softening plays in triggering shear localization. Shear banding is often interpreted as a mechanisms of failure and cracking; the present study highlights that strain partitioning facilitates the fabrication of bulk laminated materials by ECAP.
9:30 AM Invited
Slip Transmission in Ultra Fine Grain Materials: Katerina Aifantis1; Fei Shuang1; 1University of Florida
Molecular dynamics simulations are employed to capture slip transmission in BCC Fe bicrystals with a grain size ranging from 10 to 100 nm. It is illustrated that the slip mechanisms, which occur either through dislocation absorption or emission at the grain boundary, depend on the grain size but also on the grain boundary structure and chemistry. Such grain boundary effects can be accounted for by defining a mechanically induced grain boundary energy, which is independent of the thermodynamic energy used to define grain boundaries. Incorporating such energy terms within gradient plasticity allows for expressions that can predict the grain boundary strength and hence be used to tailor material properties.
9:50 AM Invited
Making Strong, Tough, Thermally-stable, and Radiation Tolerant Nanocrystalline Materials in Bulk Form: Timothy Rupert1; 1University of California, Irvine
Nanocrystalline materials are unfortunately often an exercise in futility. Efforts to make them extremely strong result in embrittlement. Process improvements that give additional grain refinement only mean that your material is more unstable against coarsening. In this talk, we discuss how the incorporation of disordered complexions into a nanocrystalline grain structure can be a possible way to solve all of the major limitations of nanocrystalline materials. We find that the ductility, toughness, strength, thermal stability, and radiation tolerance are all simultaneously increased with the incorporation of amorphous intergranular films into nanocrystalline Cu alloys. Moreover, these materials can be easily fabricated into bulk forms with simple processing, suggesting a route to commercial use in the near future. Finally, we demonstrate that these findings can be generalized to other material systems, with extension to Fe-rich alloys being of particular interest.
10:10 AM Break
10:30 AM Invited
Hierarchical Microstructure in Additively Manufactured Ti-6Al-4V and its Effect on Mechanical Properties: Jinyeon Kim1; Jenniffer Bustillos1; Atieh Moridi1; 1Cornell University
The complex relationship between Additive Manufacturing (AM) process parameters, microstructure, and resultant properties needs to be fully understood for its widespread use. In this study, selective laser melting is used to print Ti-6Al-4V. In-situ tensile tests with concurrent detailed microstructural analysis are performed. Our results show that the as-printed part develops a hierarchical microstructures, consisting of primary, secondary, and tertiary α' martensite as a result of cyclic heat treatment during selective laser melting. Upon deformation, strain localization within primary α' martensite results in microscopic ductile micro-void formation and coalescence, as well as macroscopic brittle fracture. In addition to localization inside primary α', surface steps at the boundaries of these high aspect ratio grains are formed which reveal the contribution of interfacial plasticity to the overall deformation of the material. Post Hot Isostatic Pressing (HIP) is performed on the samples and its effect on microstructure and mechanical properties is discussed.
10:50 AM
Size-dependent Dislocation-twin Interactions: Jiangwei Wang1; Guang Cao1; Ze Zhang1; Frederic Sansoz2; 1Zhejiang University; 2The University of Vermont
Dislocation-twin interactions critically control the plastic deformation and ultrahigh strength of nanotwinned metals. Here, we report a strong twin-thickness dependence of dislocation-twin interaction mechanisms from the tensile deformation of face-centered cubic metallic nanocrystals by in situ nanomechanical testing. Direct observations at atomic scale reveal that the predominant dislocation-twin interaction abruptly changes from dislocation transmission on the {111} slip planes to the unusual (100) slip plane of the twin, when the twin thickness is smaller than 4 layers. Using atomistic simulations, we find that the energy barrier for {100} slip transmission mechanism gradually decreases, with decreasing twin thickness, below the energy level required for normal (111) slip transmission, which remains identical for all twin sizes. Our in situ observations and simulations provide atomistic insights into a fundamentally new mechanism of plasticity in nanotwinned metals, down to the lowest twin size limit.
11:10 AM
Evaluation of Misorientation and Local Deformation in Bimodal Harmonic Structured Stainless Steel by Hybrid Imagings of Diffraction and Refraction Contrast Using Synchrotron Radiation X-ray: Yoshikazu Nakai1; Shoichi Kikuchi2; Daiki Shiozawa1; Kenji Nonaka1; Takumi Hase1; Yuki Nakagawa1; Kei Ameyama3; 1Kobe University; 2Shizuoka University; 3Ritsumeikan University
A stainless steel, SUS304L, with a bimodal harmonic structure was fabricated using powder metallurgy. A three dimensional grain mapping technique for polycrystalline materials, called X-ray diffraction contrast tomography (DCT), was conducted at synchrotron radiation facility to evaluate the misorientation of each crystal, and refraction contrast tomography (RCT) was conducted to measure the local strain of a specimen under tensile loading for the bimodal harmonic structured stainless steel. The average value of the total misorientation tended to increase with stress during tensile tests; however, the total misorientation of the harmonic structured SUS304L was lower than that of SUS304L with homogeneous coarse grains at comparable stress. This is consistent with the results obtained by EBSD analysis, and showed that deformation in the bimodal harmonic structured alloy is localized in the fine grained structure. The local deformation, including necking, of the specimen in tensile loading was also successfully measured by RCT.
11:30 AM Invited
Mesoscale Modeling of Deformation and Failure Behavior of Metallic Ultrafine-grained Microstructures: Avinash Dongare1; Garvit Agarwal1; Ke Ma1; 1University of Connecticut
A novel mesoscale modeling method called quasi-coarse-grained dynamics (QCGD) is used to model the deformation behavior of polycrystalline and deformation-processed ultrafine-grained (UFG) iron microstructures. The QCGD simulations extend the capability of molecular dynamics simulations to the mesoscales by reducing the number of atoms being modeled in an atomic scale microstructure using representative atoms and scaled interatomic potentials. QCGD simulations are carried out to investigate the role of heterogeneities such as grain size (ranging from 100 nm to 1 micron) on the mechanics of these materials during high rate compression and tension of Al, Al/Ni, and Fe microstructures. The framework of the QCGD simulations, the scaling relationships and the ability to reproduce MD-predicted evolution of microstructure (dislocations, phase transformation, voids, etc.) and temperatures will be presented. The applicability of the QCGD simulations to model the shock response of UFG microstructures and the capability to bridge the mesoscale gap between the current atomic-scale simulations and the continuum simulations will be presented.