International Joint Mini-Symposium on Advanced Coatings 2014

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Numerical simulation of aluminum extrusion using coated die
(2014) Bakhtiani, Tushar; El-Mounayri, Hazim; Zhang, Jing
In aluminium extrusion, the life of the die tooling components is mainly limited by wear and fatigue. Therefore reliable predictions of the amount of wear and its distribution in dies are important factors for the die design. In this study the stress location and wear depth of the tooling components were calculated using finite element models incorporating the Archards wear model. A comparative study was conducted on an extrusion die without coating and with a bilayer (TiCN + Al2O3) chemical vapor deposition (CVD) coating. Stress distribution and the amount of wear were calculated. The results generated from the simulation would help predict the service life of the components through optimizing coating thickness.
First principles study of thermodynamic properties of lanthanum zirconate
(2014) Guo, Xingye; Zhang, Jing
Lanthanum zirconia (La2Zr2O7) has become an advanced thermal barrier coating material due to its low thermal conductivity and high temperature stability. In this work, the first principles calculations were used to study the thermodynamic properties of the material. Lattice parameters, bulk and shear modulus, and specific heat of La2Zr2O7 were calculated by means of density functional theory (DFT). Hydrostatic pressure-dependent elasticity constants and bulk modulus were also studied. The thermal conductivity was calculated based on the Fourier's law. The calculated properties are in excellent agreement with the experimental and calculation results in literature.
Development of A New Coating System for The High Functional Mold in Thin-wall Casting
(2014) Kim, Eun-Hee; Jung, Yeon-Gil; Lee, Je-Hyun
A new inorganic binder system has been developed to prepare the mold having a high strength for the thin-walled casting. To increase the fracture strength at high temperature, a large amount of inorganic binder should be converted into glass phase and the generated glass phase has to be homogeneously coated on the surface of starting particles. In this work, two types of process were employed to investigate the coating and glassification efficiencies of inorganic precursor. In the first process (process I), the green body consisting of starting powder and organic binder was dipped in the inorganic precursor solution. In the second process (process II), the starting powder was coated by inorganic precursor, and then the organic binder was used to form the green body. The mold sample prepared using process II showed the higher strength value than that using process I, owing to the inclement effect on the glassfication efficiency by the loss of inorganic precursor in process I. The prepared real mold was perfectly produced and the casted product showed a clean surface without defects such as dross, nonmetallic inclusions, and crack. Consequently, the new inorganic binder system could be applied for preparing the mold for the thin-wall casting having high mechanical properties.
Effect of microarc oxidation time on electrochemical behaviors of coated bio-compatible magnesium alloy
(2014) Liu, Jiayang; Zhang, Wiejie; Zhang, Hanying; Hu, Xinyao; Zhang, Jing
Magnesium alloys are newly promising biomaterials with potential application of human bone replacement. However, there is a drawback due to their high corrosion rates. In this study, AZ31 magnesium alloys were coated using microarc oxidation (MAO) process. Two oxidation durations, 1 minute and 5 minutes, were used. The samples were immersed in the simulated body fluid (SBF) for up to seven days. Then the electrochemical behaviors of the two samples were comparatively investigated. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) experiments were used. The results show that the 5-minute MAO coated sample had a better corrosion resistance than the 1-minute MAO coated sample. The study shows processing parameters, e.g., oxidation time, can be used to design an optimized MAO-coated magnesium alloy with controlled corrosion rates.
Microstructure evolution and thermal durability with coating thickness in APS thermal barrier coatings
(2014) Lu, Z; Myoung, S W; Kim, E H; Lee, J H; Jung, Y G
The effects of the coating thickness on the delamination or fracture behavior of thermal barrier coatings (TBCs) were investigated through the cyclic furnace thermal fatigue (CFTF) and thermal shock (TS) tests. The TBCs were prepared using a NiCrAlY bond coat and an yttria-stabilized zirconia top coat, which were formed using the air plasma spray (APS) process. The thicknesses of the top coat were 200 and 400 μm, and those of the bond coat were 100 and 200 μm. TBC samples with a thickness ratio of 2:1 in the top and bond coats were employed in the CFTF and TS tests. After CFTF for 1429 cycles, the interface microstructure of the relatively thick TBC was in a sound condition without any cracking or delamination; however, the relatively thin TBC was delaminated near the interface between the top and bond coats after 721 cycles. In the TS, the TBCs were fully delaminated (> 50%) after 140 and 194 cycles for thicknesses of 200 and 400 μm in the top coat, respectively. These observations allow us to control the thickness of TBC prepared using the APS process, and the thicker TBC is more efficient in improving thermal durability in the cyclic thermal exposure and thermal shock environments.
Lamellar to Rod Eutectic Transition in the Hypereutectic Nickel- Aluminum Alloy
(2014) Que, Z P; Gu, J H; Shin, J H; Choi, H K; Jung, Y G; Lee, J H
Directional solidification experiments were carried out on the hypereutectic Ni-25 at.% Al alloy to examine the effect of growth velocity on the eutectic microstructure. The growth velocity was varied from 1 to 20 μm/s at a constant temperature gradient of 10.0 K/mm. The microstructural observations of unidirectionally solidified samples show that the lamellar eutectic growth was observed in the sample solidified at a constant velocity of 1 μm/s and the rod eutectic growth at velocities higher than 10 μm/s. A microstructural transition from lamellar to rod eutectics was achieved at the intermediate velocity. The lamellar to rod eutectic transition was shown to result from the compositional change due to the presence of strong convection in the melt. The undercooling-spacing curves showed that the average eutectic spacings for the lamellar and the rod structures were 1.6 times larger than that in the minimum undercooling for a given velocity.
First principles study on the electrochemical, thermal and mechanical properties of LiCoO2 for thin film rechargeable battery
(2014) Wu, Linmin; Hoh Lee, Weng; Zhang, Jing
Thin film rechargeable battery has become a research hotspot because of its small size and high energy density. Lithium cobalt oxide as a typical cathode material in classical lithium ion batteries is also widely used in thin film rechargeable batteries. In this work, the electrochemical, mechanical and thermal properties of LiCoO2 were systematically investigated using the first principles method. Elastic constants under hydrostatic pressures between 0 to 40 GPa were computed. Specific heat and Debye temperature at low temperature were discussed. Thermal conductivity was obtained using the imposed-flux method. The results show good agreements with experimental data and computational results in literature.
Microstructural non-uniformity and mechanical property of air plasma-sprayed dense lanthanum zirconate thermal barrier coating
(2014) Zhang, Jing; Guo, Xingye; Jung, Yeon-Gil; Li, Li; Knapp, James
Lanthanum zirconate is a promising thermal barrier coating material. In this work, imaging technique was used to characterize the microstructural non-uniformity of the coating. The imaging analyses revealed that, along the thickness of the coating, the cracks were primarily horizontal in the top and middle regions, while vertical cracks became dominant in the bottom region. The calculated porosities showed a non-uniformity (4.8%, 5.3%, and 5.5% in the top, middle, and bottom regions, respectively). They were lower than the experimentally measured one, 7.53%, using the Archimedes method. This is because imaging analysis does not take internal porosity into account. Additionally, the measured Vickers hardness was 5.51±0.25 GPa, nanoindentation hardness was 8.8±2.1 GPa, and Young's modulus was 156.00±10.03 GPa.
The 1st International Joint Mini-Symposium on Advanced Coatings between Indiana University-Purdue University Indianapolis and Changwon National University: Preface
(2014) Zhang, Jing; Jung, Yeon-Gil
The 1st international joint mini-symposium on advanced coatings between Indiana University-Purdue University Indianapolis (IUPUI) and Changwon National University (CNU) was held on March 18-20, 2014 in Indianapolis, Indiana, USA. Research papers presented in the symposium are included in this proceeding. The symposium covered recent development in advanced coatings and related functional materials. The symposium offered the students and researchers from both universities a valuable opportunity to share a wide spectrum of new knowledge of advanced coatings and related functional materials. The research topics presented in the symposium included thermal barrier coatings, bio-related coatings, nano-materials and materials for energy conversion. The symposium enabled face-to-face discussions and developed genuine friendship, which promoted international collaboration and exchange program for researcher as well as students to carry out science work together. J.Z. would like to thank the support provided by the US Department of Energy (Grant No. DE-FE0008868, program manager Richard Dunst) and International Development Fund by the IUPUI Office of Vice Chancellor for Research. Y.G.J. acknowledges the support provided by the National Research Foundation of Korea (NRF) grant funded by the Korean Government (MSIP) (No. 2011-0030058) and the Human Resources Development Program (No. 20134030200220) of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korean Government Ministry of Trade, Industry and Energy.
First principles study of structural and thermodynamic properties of zirconia
(2014) Zhang, Yi; Zhang, Jing
Due to their high melting temperature and low thermal conductivity, zirconia (ZrO2) based ceramics have been widely used for thermal barrier coating materials. This study investigates zirconia's properties using the first principles calculations. Structural properties, including band structure, density of state, lattice parameter, as well as elastic constants for both monoclinic and tetragonal zirconia were computed. Pressure based phase transition of tetragonal zirconia (t-ZrO2) was also calculated, based on tetragonal distortion and band structure under compressive pressures. The results predicted a transition from monoclinic structure to a fluorite-type cubic structure at the pressure of 37 GPa. Moreover, monoclinic zirconia (m-ZrO2) thermodynamic property calculations were carried out. Temperature-dependent heat capacity, entropy, free energy, and the Debye temperature of monoclinic zirconia, from 0 to 1000 K, were computed and compared well with those reported in literature.

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