Ultrafine-grained and Heterostructured Materials (UFGH XI): Poster Session I
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

Tuesday 5:30 PM
February 25, 2020
Room: Sails Pavilion
Location: San Diego Convention Ctr


N-22: A Comparative Study of Cu/Ta and Ti/Ta Multilayer Composites Processed by Accumulative Roll Bonding: Liya Semenchenko1; Ryan Mier2; Michael Demkowicz1; 1Texas A&M University; 2Los Alamos National Laboratory
    Accumulative roll bonding (ARB) is an effective means of synthesizing ultrafine-grained (UFG) composite metals with low mutual solubility. ARB of metal pairs with high mutual solubility is relatively unexplored. In this work, we compare ARB composites of Cu/Ta and Ti/Ta: the former having low solubility, while in the latter, solubility is high. Characterization of microstructure and mechanical properties is performed after each rolling step in an effort to identify the key microstructural features governing mechanical behavior. Our work offers insight into processing-microstructure-property relationships in UFG composite metals with high interface density.

N-23: Bulk High Strength Ultrafine Grained Silver Alloys via Powder Metallurgical Approaches: Erik Sease1; Evander Ramos1; Vladilena Gaisina2; Suveen Mathaudhu1; 1University of California Riverside; 2QuesTek Innovations LLC
    Ultrafine-grained materials have gained interest in recent years due to their unique properties when compared to their coarse-grained counterparts. In this work, microstructural refinement to the nanoscale and grain size stabilization in dilute binary Ag alloys is achieved through mechanical alloying (MA) followed by consolidation with spark plasma sintering (SPS). The mechanical properties of this alloy are probed with micro-tensile testing and micro-indentation. The microstructure is examined with electron microscopy revealing the presence of nano-scale grains and dispersoids, significantly bolstering the strength of the material as compared to that of pure unalloyed silver. The results forecast the ability to process high-strength, high-conductivity Ag alloys for electronic and structural applications.

Cancelled
N-24: Deformation Induced Grain Boundary Segregation in Nanolaminated Al-Cu Alloy: Wei Xu1; XiaoChun Liu1; XiuYan Li1; Ke Lu1; 1Institute of Metal Research Chinese Academy of Sciences
    A gradient nanostructured surface layer was formed in an Al-4 wt.% Cu alloy processed by means of surface mechanical grinding treatment at liquid nitrogen temperature.In the topmost surface layer, nanolaminated (NL) structures were found with an average thickness as small as 28 nm and a HAGB fraction of 70%. Composition analysis indicated that Cu atoms segregate at NL boundaries in the as-prepared sample, Cu concentration is about 3-4 times higher than that in the lattice. The obvious GB segregation of Cu induced by cryogenic plastic deformation is attributed dynamic interaction between Cu atoms with gliding dislocations. GB segregation of Cu is responsible for the stabilization of the NL structures with much finer structural size than that in pure Al. The deformation-induced solute segregation on GBs provides an alternative strategy to achieving stable high strength nanostructures in Al alloys.

N-25: Deformation Mechanism and Mechanical Properties of Nano/Ultrafine Grained and Heterogeneous Fe-17Cr-6Ni Austenitic Steel: Xiangtao Deng1; Chengshuai Lei1; Zhaodong Wang1; 1Northeastern University
    Deformation behavior and mechanical properties of Fe-17Cr-6Ni austenitic steel with nano/ultrafine grained microstructure and heterogeneous microstructure were studied in this investigation. With decreasing grain size, stacking fault and deformation twining gradually became the unique deformation mechanism in nano/ultrafine grained austenitic steel while in the coarse grained counterpart, deformation induced martensite transformation was always the dominant deformation mechanism. This is due to that with decreasing grain size, the critical stress for nucleating partial dislocations became smaller than that for nucleating perfect dislocations. Besides, the heterogeneous nano/ultrafine grained austenitic steel was found to possess better mechanical properties compared with homogeneous nano/ultrafine grained steel, which can be attributed to high back stress hardening and multi-stage strain hardening.

N-27: Effect of Severe Plastic Deformation on Mechanical Properties of Al6061: Vagish Mishra1; Karthik Palaniappan2; Balkrishna Rao2; Murthy H.1; 1Indian Institute of Technology Madras; 2Indian Institute of Technology Madras
     Large plastic deformation through cold-rolling refines microstructure through accumulation of plastic strains over multiple stages. Machining achieves similar large plastic strains (1-10) in a single stage to produce ultra-fine-grained chips. Effect of cold-rolling and machining on microstructure and mechanical properties of Al6061 was investigated. As-received, solution heat-treated and peak-aged plates were cold-rolled to 30%, 50% & 70% thickness reductions. Ultra-fine-grained chips were produced from low-speed orthogonal-machining under plane-strain condition, using restricted contact tool to minimize the chip curvature.Grains were equiaxed in as-received, solution-heat-treated and peak-aged samples, while they were elongated in cold-rolled bulk. In chips, grains were elongated in one direction due to severe plastic flow. Hardness and ultimate tensile strength increased with thickness reduction. Chip hardness is 60% more than as-received material due to microstructure refinement. Metal cutting (single-stage process) and >50% thickness reduction by cold-rolling (multi-stage) provide nearly same enhancement in mechanical properties (40% more than bulk).

N-28: Enhanced Mechanical Properties of Nano/Ultrafine-grained Structure Formed by Martensite Reversion in 18Cr-8Ni Austenitic Stainless Steel: Jia Liu1; Xiangtao Deng1; Zhaodong Wang1; 1Northeastern University
    The effect of grain size on high cycle fatigue behavior under axial force in 18Cr-8Ni austenitic stainless steel was investigated. By means of phase reversion process, nano/ultrafine-grained and coarse-grained structures were formed on austenitic stainless steel. The mean grain sizes are 400 nm and 12 μm, and refine the grain size can improve the fatigue strength effectively. Microstructure observations using TEM reveal that, high density dislocations, poorly developed dislocation cell-like structures and stacking faults were formed in CG steel after fatigue. In contrast, cyclic deformation microstructures of NG/UFG sample were different from that of CG steel. Dislocations in nano/ultrafine grains and dislocation cell and dislocation wall structures in deformed austenite grains were observed in NG/UFG sample.

N-29: Evolution in Mechanical Response, Phase Transformation and Texture of Titanium Aluminide Processed by High-pressure Torsion: Jae-Kyung Han1; Xi Li2; Rian Dippenaar2; Klaus-Dieter Liss3; Megumi Kawasaki1; 1Oregon State University; 2University of Wollongong; 3Guangdong Technion - Israel Institute of Technology
    Processing of an ultrafine-grained γ-based Ti-45Al-7.5Nb intermetallic compound was conducted by high-pressure torsion (HPT) up to 10 turns under 6.0 GPa at room temperature. Severe grain refinement was introduced into a 10 mm diameter disk containing a duplex microstructure by producing ultrafine laths with thicknesses of 40-100 nm after 10 turns by HPT. Micro-mechanical responses were examined by a novel nanoindentation technique. The occurrence of phase transformations and order-disorder phase transitions were confirmed by complementary analyses using lab-scale X-ray diffraction and neutron diffraction at different through-thickness sections within the processed samples. Close scrutiny revealed that the phase transformations and order/disorder phase transitions vary gradually from the sample core to the surface and hence, a significant heterogeneous texture develops as a result of HPT processing. This study demonstrates considerable potential for utilizing HPT processing for achieving enhanced microstructural development, improved mechanical properties and control of texture in Titanium Aluminides.

Cancelled
N-30: In-situ Study of Strain Distribution and Crystal Rotation of Aluminum with Tailored Grain Size Distribution: Wenqiang Gao1; Godfrey Andrew William1; 1Tsinghua University
    A combined in-situ high resolution digital image correlation (DIC) and electron backscatter diffraction (EBSD) study of the local strain distribution and crystal rotation during tensile loading has been carried out using samples of pure aluminum with a tailored grain size distribution. Samples were consolidated using spark plasma sintering to achieve a mixture of fine (1µm average grain size) and coarse (5µm average grain size) grains. The DIC results show a wide range of heterogeneity both between and within different grains. Although a significant amount of strain is carried by the coarse grains, some localized strain is also carried by the fine grains. A different crystal rotation behavior is also seen in the coarse and fine grains in term of intergranular misorientation and lattice rotation path. The observations are discussed in terms of the mechanical properties of samples with tailored microstructures for optimized combinations of strength and ductility.

N-31: Investigations on the Microstructure and Properties of Ultrafine-grained Cu-Al Materials Jointed with Friction Stir Welding: Yue Zhang; Hongyang Yu1; Dongbo LIU1; Xiaoguang Yuan1; 1Shenyang University of Technology
    Compared with conventional coarse grain materials, nanomaterials have excellent mechanical properties. However, there is a grain coarsening tendingcy of such materials under annealing. Consequently, nanomaterials bonding is the key technology that restricts the application of nanomaterials. In this study, the Cu/Al joints were connected by friction stir welding, the rotating speed of stirring head was selected 800rpm, 1000rpm, and the welding speed was 50mm/min respectively. The results show that under a parameter of 1000rpm, with a welding speed of 50mm/min, there observed sufficient diffusion interface in the joint of coarse-grained aluminum (CG-Al, ~20 μm) with an ultrafine-grained copper(UFG-Cu, ~200 nm), The grain size of ~3μm, the bonding strength of ~264 MPa as well as microhardness of 180 Hv. Under the condition of 800rpm-50mm/min, the interfacial bonding strength of CG-Al/UFG-Cu was higher than that of CG-Al/CG-Cu. Therefore, The comprehensive mechanical properties of CG-Al/UFG-Cu were the best under the condition of 1000rpm-50mm/min.

N-32: Joining of Ultrafine Grained Aluminium by Friction Stir Welding-processing, Microstructure and Properties of Similar and Dissimilar Welds: Marta Orlowska1; Lech Olejnik1; Andreas Huetter2; Norbert Enzinger2; Malgorzata Lewandowska1; 1Warsaw University of Technology; 2Graz University of Technology
    Severe plastic deformation processes allow to produce materials with grain size reduced below 1 µm. It causes an increase in mechanical properties, however, such materials feature limited thermal stability. Therefore, advanced joining techniques are required to preserve refined microstructure. In the present study, Incremental ECAP and Friction Stir Welding have been chosen as deformation and joining techniques, respectively. Similar and dissimilar (the samples with different deformation strain were joined) welds were obtained and featured good quality. The evolution of microstructure and mechanical properties from the base material to the stir zone was investigated. For this purpose SEM/EBSD, TEM, microhardness measurements and tensile tests were performed. The results revealed a grain growth in the stir zone to the value of 2.1-3.7 µm. It caused a drop of mechanical properties in comparison to ultrafine grained base materials but an increase in comparison to annealed aluminium.