Microstructural and kinetic investigation on the suppression of grain growth in nanocrystalline copper by the dispersion of silicon carbide nanoparticles

Akbarpour, M.R.,Farvizi, M.,Kim, H.S. Elsevier Ltd 2017 Materials & Design Vol.119 No.-

<P>In this paper, the thermal stability and grain growth kinetics of nanocrystalline Cu, reinforced with SiC nanoparticles and obtained using a mechanical milling process, were investigated during isothermal annealing. The presence of the nanoparticles in the nanocrystalline copper matrix resulted in a significant decrease in grain growth, the formation of partially textured microstructure and twin boundaries at higher temperatures, and an increase in the volume fraction of recrystallized grains, as estimated by grain orientation spread, in comparison to unreinforced Cu during annealing. The lower volume fraction of recrystallized grains at higher temperatures was attributed to dynamic recovery. Normal grain growth was observed in the annealing range of 400-600 degrees C, and significant abnormal grain growth was observed at higher temperatures. An analysis of the grain growth kinetics in the temperature range of 400-600 degrees C revealed a time exponent of n approximate to 3.6 and activation energy of approximate to 34 kJ mol(-1), based on the parabolic equation. The calculated activation energy for grain growth in the SiC dispersion strengthened Cu was found to be less than that of nanocrystalline Cu. The low activation energy and high thermal stability were attributed to high lattice strain and the retarding effect of nanoparticles by the Zener mechanism. (C) 2017 Elsevier Ltd. All rights reserved.</P>

Application of Ca-doped mesoporous silica to well-grouting cement for enhancement of self-healing capacity

Lee, S.W.,Jo, M.,Kim, J.W.,Kim, T. Elsevier Ltd 2016 Materials & Design Vol.89 No.-

<P>Carbonation has been considered as an alternative to prevent CO2 leakage. In this study, calcium-doped mesoporous silica (CDMS) was introduced into Portland cement as a promoter of carbonation. An admixture of CDMS and American Petroleum Institute (API) Class G Portland cement exposed to CO2-saturated water was analyzed under geologic sequestration conditions (40 degrees C and 80 MPa) to assess the carbonation properties and self-healing effect of CDMS for CO2 storage. The capacity of CDMS to synthesize CaCO3 from CO2 via carbonation was identified in an in vitro crystallization test. Analysis of the cut surface of a cement core showed the rapid synthesis of CaCO3 including calcite and aragonite. Rietveld analysis was employed for quantitative phase analysis. The quantitative analysis of the cement carbonation showed that tricalcium silicate (C3S) and dicalcium silicate (C2S) play important roles in cement carbonation. Several crystal phases of CaCO3 were identified in this study including calcite, aragonite and amorphous CaCO3. X-ray diffractometry (XRD), a field emission-scanning electron microscope (FE-SEM) equipped with an energy dispersive X-ray spectrometer (EDS), Si-29 MAS-NMR (magic angle spinning-nuclear magnetic resonance) spectrometry, thermogravimetiy-differential thermal analysis (TG-DTA) and FT-IR (Fourier transform infrared spectroscopy) were applied to characterize the admixture. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Development of Mo@?Ni@?Si@?B metallic glass with high thermal stability and H versus E ratios

Kim, J.,Kyeong, J.S.,Ham, M.H.,Minor, A.M.,Kim, D.H.,Park, E.S. Elsevier Ltd 2016 Materials & Design Vol.98 No.-

<P>We report a novel Mo-Ni-Si-B metallic glass which can be solidified into fully amorphous state by melt-spinning process, with high crystallization onset temperature of over 1100 K, extremely high Vickers hardness of 27.5 +/- 2.2 GPa and relatively low Young's modulus of 364.3 +/- 6.6 GPa. The dense cluster-packing model suggests that the addition of boron up to 10 at.% can occupy vacant cluster-interstices of (Mo, Ni)-Si cluster arrays, which results in a more efficiently dense-packed cluster structure, destabilizes the formation of nanocrystalline phases, and systematically increases the glass-forming ability (GFA) in Mo-Ni-Si-B alloys, The GFA parameters that do not directly rely on T-g, such as Delta T and epsilon parameter, show greater reliability to evaluate GFA for Mo-Ni-Si-B metallic glass exhibiting no clear T-g. The H/E and H-2/(2E) ratios of the newly developed Mo-Ni-Si-B metallic glass, which reflect wear resistance and resilience, exhibit the highest values among various hard ceramic materials as well as metallic glass-forming alloys developed up to now. These advantages of Mo-Ni-Si-B metallic glass can be used more widely to forma high temperature wear-resistant coating layer on various substrates. Furthermore, the same idea might be used to form a metallic glass-nitride nanocomposite coating layer by reactive deposition in N-2 ambient, with highly lubricative properly and high wear-resistance, especially at high temperature. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Study of pulsed-DC sputtering induced Ge₂Sb₂Te₅ thin films using facile thermoelectric measurement

Kumar, M.,Vora-ud, A.,Seetawan, T.,Han, J.G. Elsevier Ltd 2016 Materials & Design Vol.98 No.-

<P>Thermoelectric measurement is an exhaustive exercise for the case of thin films, requiring meticulous attention to the thermal contact interfaces and the instrumentation. Usually, different set-ups are combined for the temperature dependent measurement of different thermoelectric key quantities. Here, a facile 6-probe measurement set-up is presented, which can measure Seebeck coefficients and electrical properties of thin films in the temperature range of 300 K-600 K. Using this set-up, the thermoelectric properties of Ge2Sb5Te5 thin films, prepared with pulsed DC magnetron sputtering method are studied. The effects of working pressure, post-deposition thermal treatment and variation of film thickness on the microstructure, surface, electrical and thermoelectric properties are investigated systematically. Plasma diagnostics, performed using optical emission spectroscopy provided the information about various radicals' excitations and the electron temperature. Microstnictural studies show the phase transformation from amorphous to metastable cubic phase. FESEM study exhibits highly dense films with uniform grains compactness. It has been found that lowering average crystallite size by optimum electron temperature and pressure conditions governs the enhancement in Seebeck coefficient. The throughput of process >400 nm/min, and obtained Seebeck coefficients values 271.50 mu V/K are highly promising for industrial utilization. (C) 2016 Elsevier Ltd. All lights reserved.</P>

Surface energy and wettability control in bio-inspired PEG like thin films

Javid, A.,Kumar, M.,Wen, L.,Yoon, S.,Jin, S.B.,Lee, J.H.,Han, J.G. Elsevier Ltd 2016 Materials & Design Vol.92 No.-

<P>Tailoring of chemical functionalities in polymer films can induce interesting biocompatibility, however the sequential process of polymerization followed by functionalization imposes surface-interface complexities and inhomogeneity of functional groups across the thickness. Here, a single-step plasma process, enabling the simultaneous polymerization-functionalization, is demonstrated to control the surface energy and wettability of polyethylene glycol-like thin films. Chemical studies, carried out by Fourier transform infra-red spectroscopy and X-ray photoelectron spectroscopy, confirm the evolution and enhancement in amide functionalities, owing to the increase in the electronic transitions related to nitrogen based ions/radicals (independently confirmed by optical emission spectroscopy). In present case, the evolution and control over amide functionalities lead to the enhancement in wettability and surface energy tailoring in 60.5-67.5 mJ/m(2) range. Excellent growth of L-929 fibroblast cells is obtained by the synergic contribution of plasma power and N-2 flow rate via enriching the amide functionalities in these films. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Growth and residual stresses in the bonded compliant seal of planar solid oxide fuel cell: Thickness design of window frame

Jiang, W.,Zhang, Y.C.,Zhang, W.Y.,Luo, Y.,Woo, W.,Tu, S.T. Elsevier Ltd 2016 Materials & Design Vol.93 No.-

<P>Bonded compliant seal (BCS) is a new sealing method for planar solid oxide fuel cell. The BCS design uses a thin foil to bond the cell and window frame, which generates a multilayer structure. However, the high temperature bonding generates large residual stresses that greatly affect the fracture. This paper presents a numerical method and neutron diffraction measurement to study the residual stress, and effect of window frame thickness has been discussed. A grain boundary diffusion model incorporated with a power-law creep constitutive model is developed to calculate the growth stress in the oxide film. Then, the thermal elasto-plastic finite element method is applied to calculate the thermal stress. A neutron diffraction experiment is performed to measure the through thickness stresses. A good agreement is found between the calculation results and the neutron diffraction measurements. Compressive stress is generated in the oxide scale because of the substrate constraint. Furthermore, a competition exists between the generation of growth stress and the creep relaxation in the oxide layer. The residual stresses in the oxide layer decrease with the decrease in the substrate thickness. The thicknesses of the window frame and foil are designed to be 500 and 50 mu m, respectively. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Formation mechanism of typical onion ring structures and void defects in friction stir lap welded dissimilar aluminum alloys

Yoon, T.J.,Yun, J.G.,Kang, C.Y. Elsevier Ltd 2016 Materials & Design Vol.90 No.-

<P>The formation mechanism for typical onion ring structure and void defect with heat input during FSLW was continuously visualized by an exit-hole continuous observation technique. Based on this result, the compatibility between microstructure, microtexture, element maps and strain maps using electron backscattered diffraction (EBSD) with the chemical indexing assisted by EDS analysis was simultaneously investigated. The results revealed that the threaded probe was significantly correlated to typical onion ring structure and the onion structure formed as soon as it touched the probe. This result is different from the results so far. On the other hand, the remnant of original interface between top and bottom plates after FSLW and asymmetrical flow around rotating tool were significantly correlated to the formation of void defect in low heat input condition. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Thermal metallurgical analysis of GMA welded AH36 steel using CFD-FEM framework

Cheon, J.,Kiran, D.V.,Na, S.J. Elsevier Ltd 2016 Materials & Design Vol.91 No.-

<P>A temporal combination of CFD mass and heat transfer, and FEM conductive heat transfer analysis was conducted using a proper temperature history implantation scheme. The phase distribution in an AH36 steel weldment was predicted and compared with experimental results. The numerical phase fraction estimation was performed using the critical austenite temperature model in the heating process as a function of heating rate. The CCT information based transformation starting and finishing temperature, and the maximum phase fraction models were utilized with instant cooling rate in the cooling process. The thermal analysis result agreed well with the FZ shape and measured temperature history. The calculated hardness slightly overestimated the measured hardness. The steep reduction of hardness in the HAZ and the tempered zone was much more affected by the change in austenite critical temperature than the cooling rate. Based on the potential results of this work, predicting weldment deformation by considering phase transformation will be extended. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Molecular simulation for thermoelectric properties of c-axis oriented hexagonal GeSbTe model clusters

Vora-ud, A.,Rittiruam, M.,Kumar, M.,Han, J.G.,Seetawan, T. Elsevier Ltd 2016 Materials & Design Vol.89 No.-

<P>Using a combination of molecular orbital and molecular dynamics simulations, electronic and thermoelectric properties of GeSbTe model clusters are presented. The unit cells of Ge13Sb20Te52, Ge7Sb12Te40 and Ge14Sb6Te26 model clusters are designed corresponding to GeSb2Te4, GeSb4Te7 and Ge2Sb2Te5 compositions in hexagonal phase, oriented in the c-axis direction. The electronic structures of clusters have been simulated by discrete-variational molecular orbital calculation using Hartree-Fock-Slater approximation to determine the electrical conductivity and Seebeck coefficients in Mott expression. For thermal properties, molecular dynamics simulations have been employed on clusters in amorphous, cubic and hexagonal phases using Verlet's algorithm and subsequently using Green-Kubo relation for lattice thermal conductivity. We assumed inter-atomic interaction, defined by the Morse-type potential function added to Busing-Ida potential function, which considers partial electronic charges on the ions, bond length of the cation-anion pair, and depth and shape of the potential. Based on our simulations, detailed variation of electrical conductivity, carrier thermal conductivity, lattice thermal conductivity, Seebeck coefficients, power factor and figure of merit, are presented as a function of temperature in 300-700 K range. Thermoelectric parameters obtained in present study were compared and explained with those of experimentally results of Ge2Sb2Te5 composition in hexagonal phase. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Joining of metal-ceramic using reactive air brazing for oxygen transport membrane applications

Raju, K.,Muksin,Kim, S.,Song, K.s.,Yu, J.H.,Yoon, D.H. Elsevier Ltd 2016 Materials & Design Vol.109 No.-

<P>This study examined the joining of dense Ce0.9Gd0.1O2 (-) (delta)-La0.6Sr0.4Co0.2Fe0.8O3 (-) (delta) (GDC-LSCF) ceramics to high temperature metal alloys for the fabrication of multilayered oxygen transport membrane (OTM) stacks. Reactive air brazing using a silver-based paste was performed at 1050 degrees C for 30 min in air to join GDC-LSCF/high temperature alloys, such as AISI 310S, Inconel 600 and Crofer 22 APU. The effects of the various filler materials, including CuO, GDC, LSCF, and GDC-LSCF mixture, in the Ag paste were also examined. The Ag-10 wt% CuO braze filler ensured in a reliable and compact joining without the formation of cracks and voids at the joining interface, while the addition of other ceramic fillers resulted in incomplete joining. Although none of the GDC-LSCF/metal alloy joints showed gas leakage at room temperature, the GDC-LSCF/Crofer joint only maintained the gas-tightness up to 800 degrees C under pressurized air up to 7 bars, which was explained by the microstructural rigidness of the oxide layer formed on the filler/alloy interface at high temperatures. This was supported by the minimal decrease in shear strength of the GDC-LSCF/Crofer joint, which was 91.1 and 88.3 MPa for the as-brazed and isothermally aged joint at 800 degrees C for 24 h in air, respectively. (C) 2016 Published by Elsevier Ltd.</P>