Ultrafine-grained and Heterostructured Materials (UFGH XII): Processing, Microstructure & Property II
Sponsored by: TMS: Shaping and Forming Committee
Program Organizers: Penghui Cao, University of California, Irvine; Xiaoxu Huang, Chongqing University; Enrique Lavernia, Texas A&M University; Xiaozhou Liao, University of Sydney; Lee Semiatin, MRL Materials Resources LLC; Nobuhiro Tsuji, Kyoto University; Caizhi Zhou, University of South Carolina; Yuntian Zhu, City University of Hong Kong

Thursday 8:30 AM
March 3, 2022
Room: 262A
Location: Anaheim Convention Center

8:30 AM  Invited
Bulk Nanostructured Metallic Materials with Superior Multifunctional Properties: Ruslan Valiev1; Xiaozhou Liao; 1UFA State Aviation Technical University
    Multiple recent studies have proved severe plastic deformation (SPD) techniques as a very reliable approach to produce nanostructured metals with significantly improved mechanical and functional properties, the latter affected by several factors, including ultrafine grains and also the defect structure of their boundaries. This report presents the results of complex studies of the formation of different grain boundaries (low angle and high angle ones, special and random, equilibrium and non-equilibrium including grain boundary segregations and precipitations) in nanostructured materials processed using SPD. This entails the materials with superior multifunctional properties, i.e. the combination of high mechanical and functional properties (corrosion and radiation resistance, electrical conductivity, etc.) that are induced by grain boundary design. Particular emphasis is laid on the physical nature and the use of multifunctional nanomaterials in products for their innovative applications in medicine and engineering.

9:00 AM  
Deformation Mechanisms of Laser Rapid Solidified Al–Si Heterostructures: Bingqiang Wei1; Wenqian Wu1; Amit Misra2; Jian Wang1; 1University of Nebraska-Lincoln; 2University of Michigan
    Using laser rapid solidification (LRS) techniques, as-cast Al–20wt.% Si alloys was modified to achieve a heterogeneous microstructure which was consisted of micro-scale Al dendrites (1-2 µm) and ultrafine Al-Si eutectic with Si nanofibers (40-50 nm). In-situ SEM tension tests revealed that the heterostructured Al-Si alloys exhibit high strength (>600 MPa), good ductility (>10%) and high strain hardening rate. These superior mechanical properties were ascribed to the strong synergistic effect between soft Al dendrites and hard Al-Si eutectic structure. Plastic deformation commences in soft Al dendrites through dislocations, and high strain hardening rate develops associated with dislocations pileup in soft Al grain. With the increase in flow strength, ultrafine Al-Si eutectic plastically deforms by dislocations in Al matrix. Si nanofibers act as strong barriers for dislocations motion and sites for dislocations accumulation, developing high incompatibility of plastic deformation and leading to fracture of Si nanofibers.

9:20 AM  
Significance of Grain Refinement on Micro-mechanical Properties and Structures of Additive-manufactured CoCrFeNi High-entropy Alloy: Jae-Kyung Han1; Yulia O. Kuzminova2; Stanislav A. Evlashin2; Jae-il Jang3; Klaus-Dieter Liss4; Megumi Kawasaki1; 1Oregon State University; 2Skolkovo Institute of Science and Technology; 3Hanyang University; 4Guangdong Technion - Israel Institute of Technology
    An additive-manufactured high-entropy alloy (HEA) CoCrFeNi having an f.c.c structure was processed by high-pressure torsion (HPT) at room temperature up to 8 turns under 6.0 GPa. Significance of grain refinement was investigated on their mechanical properties and microstructures. Successful grain refinement was introduced within the processed disks containing an equiaxed grain structure with an average size of 90 nm after 8 turns by HPT. Structural evolution examined by X-ray diffraction analysis demonstrates a decrease in crystallite size and an increase in lattice parameter. Mechanical responses on different length-scales were examined by Vickers microhardness and nanoindentation which reveal the high strain hardenability and increased plasticity of the nanostructured HEA. This study demonstrates considerable potential for utilizing severe plastic deformation for exploring post-manufacturing treatments to enhance physical and mechanical properties in additive-manufactured HEAs

9:40 AM  
Strengthening Mechanisms in Dilute Ultrafine-grained Ag Alloys Processed by Top-down and Bottom-up Approaches: Erik Sease1; Evander Ramos1; Peter Jacobson2; Manuel Esparragoza2; Thomas Kozmel2; Suveen Mathaudhu3; 1University of California Riverside; 2Questek Innovations LLC; 3University of California, Riverside/Pacific Northwest National Laboratory
     In this work, microstructural refinement to the ultrafine-grained scale and grain stabilization in dilute Ag alloys is achieved through two separate processing methods: by a combination of mechanical alloying (MA) and spark plasma sintering (SPS), and by high pressure torsion (HPT). The mechanical properties are probed through micro-indentation and micro-scale mechanical testing, and the microstructure is examined with electron microscopy revealing the presence of multiple strengthening mechanisms, significantly bolstering the strength of the material as compared to that of pure unalloyed and unprocessed silver. The results forecast the ability to process high-strength, high conductivity Ag alloysfor electronic and structural applications.

10:00 AM Break

10:20 AM  
Strength Softening Mitigation in Bimodal Nanostructured Metals: Han Wang1; Penghui Cao1; 1University of California, Irvine
    Conventional metals with homogenous grain size experience strength softening with decreasing grain size to dozen nanometers. In this work, we reveal that the softening rate can be controlled by tailoring structural heterogeneity. By increasing the size ratio of large and small grains in a bimodal structured metal, we find the softening rate in the inverse Hall-Petch regime is considerably lowered, and this softening mitigation is mediated by nucleation and storage of extended dislocations in large grains. Consequently, the bimodal structured systems exhibit a smaller strain rate sensitivity as compared to their homogeneous counterparts. These findings shed light on the deformation mechanisms underlying extraordinary mechanical behaviors of materials with structural heterogeneity.

10:40 AM  
Evolution of Microstresses during Elasto-plastic Transition under In Situ Tensile Loading of Harmonic Structure Materials by Synchrotron X-ray Diffraction: Elis Sjogren1; Wolfgang Pantleon2; Ulrich Lienert3; Zoltan Hegedüs3; Kei Ameyama4; Dmyto Orlov1; 1Lund University; 2Technical University of Denmark; 3Deutsches Elektronen-Synchrotron; 4Ritsumeikan University
     Harmonic structure materials are known for enhanced structural performance without altering chemical composition. They have a bimodal grain-size distribution, with fine grains forming a continuous network enclosing islands of coarser grains. The elasto-plastic transition of such materials under mechanical loading needs to be understood. Differences in average behavior between coarser and finer grains were investigated in harmonic structure Ni during in situ tensile testing up to 4% strain using high-energy X-rays at the synchrotron beamline P21.2 at PETRA III. For enabling line profile analysis, an algorithm for separating the diffraction profiles originating from the respective grain fractions was developed.The performed line profile analysis allows new insights on the elasto-plastic transition of harmonic structure materials. For instance, stress partitioning and that each grain fraction has a distinct work-hardening behavior. Moreover, the work-hardening rate of coarse grains within the harmonic structure material is altered compared to homogenous coarse-grained material.