Compressive creep behavior of hot-pressed Mg_1.96Al_0.04Si_0.97Bi_0.03

Michi, Richard A.,Kim, Gwansik,Kim, Byung-Wook,Lee, Wooyoung,Dunand, David C. Elsevier 2018 Scripta materialia Vol.148 No.-

<P><B>Abstract</B></P> <P>The compressive creep behavior of hot-pressed Mg<SUB>1.96</SUB>Al<SUB>0.04</SUB>Si<SUB>0.97</SUB>Bi<SUB>0.03</SUB>, a promising thermoelectric material, is investigated at 500 °C. At stress levels between 81 and 212 MPa, dislocation creep with stress exponent <I>n</I> = 7.6 ± 0.3 is observed. No diffusional creep is observed, likely attributable to a dispersion of ~1 μm Bi-, Al-, and O- rich particles which pin grain boundaries. Mg<SUB>1.96</SUB>Al<SUB>0.04</SUB>Si<SUB>0.97</SUB>Bi<SUB>0.03</SUB> exhibits similar creep behavior to previously studied silicides, but is significantly more creep resistant than other thermoelectric materials, PbTe and Bi<SUB>2</SUB>Te<SUB>3</SUB>. This makes Mg<SUB>1.96</SUB>Al<SUB>0.04</SUB>Si<SUB>0.97</SUB>Bi<SUB>0.03</SUB> an excellent material for thermoelectric power generation systems subjected to high stresses and temperatures.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Experimental and modeling study of compressive creep in 3D-woven Ni-based superalloys

Cho, Hoon-Hwe,Erdeniz, Dinc,Sharp, Keith W.,Dunand, David C. Elsevier 2018 ACTA MATERIALIA Vol.155 No.-

<P><B>Abstract</B></P> <P>Micro-architectured Ni-based superalloy structures, with Ni-20Cr-3Ti-2Al (wt.%) composition and γ/γ′-microstructure, are created by a multi-step process: (i) non-crimp orthogonal 3D-weaving of ductile, 202 μm diameter Ni-20%Cr wires, (ii) gas-phase alloying with Al and Ti, (iii) simultaneous transient-liquid phase (TLP) bonding between wires and homogenization within wires <I>via</I> interdiffusion, (iv) solutionizing to create a single-phase solid solution, and (v) aging to precipitate the γ′ phase. The creep behavior of these 3D-woven γ/γ′ nickel-based superalloys is studied under uniaxial compression <I>via</I> experiments at 825 °C and <I>via</I> finite element (FE) analysis, using a 3D model of the woven structures obtained through X-ray micro-tomography. The creep strain rate for the woven Ni-based superalloy is higher than that for the bulk superalloy due to the lower solid volume fraction of the woven structure, while the creep exponents are identical. The compressive creep behavior is sensitive to the geometry of the woven structures: fewer wires perpendicular to the load and fewer bonds between wires cause lower creep resistance of the woven structure, due to a reduction in load transfer from the longitudinal wires (which are primarily load-bearing) and the perpendicular wires. Creep buckling of longitudinal wires drastically reduces creep resistance of the woven structure, confirming the importance of maintaining longitudinal wires vertical and parallel to the uniaxial compression direction. Finally, reducing wire cross-section, <I>e.g., via</I> oxidation, reduces creep resistance. The oxidation kinetics of the wire structures at 750, 825, and 900 °C displayed parabolic rate constants comparable to commercial Ni-based superalloys, but indicates that up to 35% of the wire cross-section is oxidized after 7 days at 825 °C, such that oxidation-resistant coatings are needed for long-term use in oxidative environment.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Surface-oxidized, freeze-cast cobalt foams: Microstructure, mechanical properties and electrochemical performance

Park, Hyeji,Cho, Hoon-Hwe,Kim, Kyungbae,Hong, Kicheol,Kim, Jae-Hun,Choe, Heeman,Dunand, David C. Elsevier 2018 ACTA MATERIALIA Vol.142 No.-

<P>Cobalt with anisotropic open porosity is fabricated by directional solidification of aqueous slurries of nanometric Co3O4 powder where ice dendrites push powders into aligned interdendritic spaces, followed by ice sublimation, reduction of the oxide to metallic Co powders, and sintering of these Co powders into parallel lamellae. As the Co3O4 powder slurry fraction decreases (from 10 to 4 vol%), Co lamellae width in the final foam also decreases (from 93 to 8 gm) while foam porosity increases (from 66 to 85%). A drop in solidification temperature (from -10 to -50 degrees C) decreases porosity (from 77 to 63%) and lamellae width (from 11 to 5 mu m) at a constant 8 vol% slurry fraction. Finally, with increasing sintering time (for -10 degrees C solidification temperature and 8% slurry fraction), Co foam porosity decreases (from 77 to 68%) and lamella width strongly increases (from 10 to 59 gm), consistent with sintering induced coalescence of lamellae. The Co foams exhibit high strength but relatively low stiffness as compared to simple theoretical models, consistent with internal Co lamella buckling. A uniform Co oxide layer is grown by oxidation to create an active coating on the Co lamellae useful for lithium-ion storage. A coin-cell test carried out on the oxidized Co foam demonstrates a capacity (1283 mAhg(-1)) almost twice that of a control oxidized Co foil anode, owing to its considerably larger surface area. Finite-element analysis is used to compute stresses and plastic strain evolutions during the lithiation process to understand the effect of oxide layer thickness and roughness, and micropores within the Co lamellae. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.</P>

Microstructure and compressive behavior of ice-templated copper foams with directional, lamellar pores

Park, Hyeji,Choi, Myounggeun,Choe, Heeman,Dunand, David C. Elsevier Sequoia 2017 Materials science & engineering Structural materia Vol.679 No.-

<P><B>Abstract</B></P> <P>Copper foams are fabricated by directional freezing of aqueous suspensions of nanometric CuO powders followed by ice sublimation, reduction to Cu in Ar–5% H<SUB>2</SUB> gas and sintering. During slurry solidification, parallel, lamellar, centimeter-long ice dendrites grow, pushing the CuO powders into lamellar interdendritic spaces. Upon subsequent ice sublimation, the ice dendrites create lamellar pores surrounded by CuO walls that are subsequently reduced to copper and sintered; these ice-templated walls display surface micropores and, depending on the reduction/sintering parameters, internal micropores. Varying the main processing parameters – powder fraction in the slurry (from 13 to 19vol%) and casting temperature (from −10 to −30°C) – has a strong effect on the foam microstructure: (i) porosity (varying from 45% to 73%) is inversely related to slurry powder fraction, (ii) oriented lamellar macropores width increases from 15 to 64µm with decreasing slurry fraction and increasing freezing temperature and (iii) oriented lamellar Cu wall width increases from 19 to 63µm with increasing slurry fraction and freezing temperature. The resulting Cu foams show oriented, lamellar macropores (beneficial to permeability) and walls micropores (which increase the surface area) and are promising for use in electrochemical cells given the simplicity, scalability, low cost, and microstructure tunability associated with the ice-templating process. The ice-templated Cu foams, with pore directions parallel and perpendicular to the direction of compressive loading, show ductile compressive behavior with high yield stress, ductility and energy absorption; they are compared to model predictions and literature data of Cu lotus foams with elongated, cylindrical pores.</P>

Printed Origami Structures (Adv. Mater. 20/2010)

Ahn, Bok Yeop,Shoji, Daisuke,Hansen, Christopher J.,Hong, Eunji,Dunand, David C.,Lewis, Jennifer A. WILEY-VCH Verlag 2010 Advanced Materials Vol.22 No.20

<B>Graphic Abstract</B> <P>Bok Y. Ahn, Jennifer Lewis, and co-workers report on p. 2251 a new method for creating complex 3D structures that combines direct-write assembly with a wet-folding origami technique. Planar lattices composed of a titanium hydride ink are printed, and then folded, rolled, or molded into the desired shape. These 3D objects are then transformed into metallic or ceramic structures by thermal annealing. <img src='wiley_img_2010/09359648-2010-22-20-ADMA201090069-content.gif' alt='wiley_img_2010/09359648-2010-22-20-ADMA201090069-content'> </P>

Microstructure and Mechanical Properties of Reticulated Titanium Scrolls

Hong, Eunji,Ahn, Bok Y.,Shoji, Daisuke,Lewis, Jennifer A.,Dunand, David C. WILEY‐VCH Verlag 2011 Advanced Engineering Materials Vol.13 No.12

<P><B>Abstract</B></P><P>Reticulated titanium scrolls are produced by printing titanium hydride lattices composed of two orthogonal layers of ink filaments, which are then rolled into cylinders and reduced to titanium upon partial vacuum sintering. The resulting three‐dimensional titanium scrolls contain a hierarchical pore size distribution composed of macroporosity between patterned filaments and micropores within each filament. These reticulated architectures exhibit an attractive combination of stiffness, strength, and ductility when tested in uniaxial compression.</P>

Printed Origami Structures

Ahn, Bok Yeop,Shoji, Daisuke,Hansen, Christopher J.,Hong, Eunji,Dunand, David C.,Lewis, Jennifer A. WILEY-VCH Verlag 2010 Advanced Materials Vol.22 No.20

<B>Graphic Abstract</B> <P>Printed origami structures are fabricated by combining direct-write assembly of planar lattices with a wet-folding origami technique. This novel approach provides a low-cost, versatile route to create three-dimensional structures from diverse materials, whose shapes range from simple polyhedra to intricate origami forms. <img src='wiley_img_2010/09359648-2010-22-20-ADMA200904232-content.gif' alt='wiley_img_2010/09359648-2010-22-20-ADMA200904232-content'> </P>

Finite element analysis of a tin oxide-coated copper foam anode in lithium-ion batteries based on a fully coupled diffusionalmechanical modeling

K. J. Jeong(정경재),H. -H. Cho(조훈휘),H. N. Han(한흥남),D. C. Dunand(David C. Dunand) 한국소성가공학회 2019 한국소성가공학회 학술대회 논문집 Vol.2019 No.5

<i>In operando</i> X-ray diffraction strain measurement in Ni₃Sn₂ – Coated inverse opal nanoscaffold anodes for Li-ion batteries

Glazer, Matthew P.B.,Wang, Junjie,Cho, Jiung,Almer, Jonathan D.,Okasinski, John S.,Braun, Paul V.,Dunand, David C. Elsevier 2017 Journal of Power Sources Vol.367 No.-

<P><B>Abstract</B></P> <P>Volume changes associated with the (de)lithiation of a nanostructured Ni<SUB>3</SUB>Sn<SUB>2</SUB> coated nickel inverse opal scaffold anode create mismatch stresses and strains between the Ni<SUB>3</SUB>Sn<SUB>2</SUB> anode material and its mechanically supporting Ni scaffold. Using <I>in operando</I> synchrotron x-ray diffraction measurements, elastic strains in the Ni scaffold are determined during cyclic (dis)charging of the Ni<SUB>3</SUB>Sn<SUB>2</SUB> anode. These strains are characterized using both the center position of the Ni diffraction peaks, to quantify the average strain, and the peak breadth, which describes the distribution of strain in the measured volume. Upon lithiation (half-cell discharging) or delithiation (half-cell charging), compressive strains and peak breadth linearly increase or decrease, respectively, with charge. The evolution of the average strains and peak breadths suggests that some irreversible plastic deformation and/or delamination occurs during cycling, which can result in capacity fade in the anode. The strain behavior associated with cycling of the Ni<SUB>3</SUB>Sn<SUB>2</SUB> anode is similar to that observed in recent studies on a Ni inverse-opal supported amorphous Si anode and demonstrates that the (de)lithiation-induced deformation and damage mechanisms are likely equivalent in both anodes, even though the magnitude of mismatch strain in the Ni<SUB>3</SUB>Sn<SUB>2</SUB> is lower due to the lower (de)lithiation-induced contraction/expansion.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Lithiation-induced strains quantified in a Ni<SUB>3</SUB>Sn<SUB>2</SUB> inverse opal anode <I>in operando</I>. </LI> <LI> Lithiation induces compressive average strains in Ni inverse opal scaffold. </LI> <LI> Ni inverse opal scaffold strain distribution reversibly broadens upon lithiation. </LI> <LI> Three measured volumes show similar cyclic strain averages and distributions. </LI> <LI> Ni<SUB>3</SUB>Sn<SUB>2</SUB> measured cyclic strains are similar to prior Si inverse opal anode studies. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

In Operando Strain Measurement of Bicontinuous Silicon-Coated Nickel Inverse Opal Anodes for Li-Ion Batteries

Glazer, Matthew P. B.,Cho, Jiung,Almer, Jonathan,Okasinski, John,Braun, Paul V.,Dunand, David C. Wiley Blackwell (John Wiley Sons) 2015 ADVANCED ENERGY MATERIALS Vol.5 No.14