Development of A New Coating System for The High Functional Mold in Thin-wall Casting

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 thermal cycling frequency on the durability of Yb-Gd-Y-based thermal barrier coatings

The effects of thermal cycling frequency and buffer layer on the crack generation and thermal fatigue behaviors of Yb–Gd–Y-stabilized zirconia (YGYZ)-based thermal barrier coatings (TBCs) were investigated through thermally graded mechanical fatigue (TGMF) test. TGMF tests with low- (period of 10 min) and high-frequency (period of 2 min) cycling were performed at 1100 °C with a 60 MPa tensile load. Different cycling frequencies in TGMF test generate two kinds of crack propagation modes. The sample with low-frequency cycling condition shows penetration cracks in the YGYZ top coat, and multiple narrow vertical cracks are generated in high-frequency cycling. To enhance the thermomechanical properties, different buffer layers were introduced into the TBC systems, which were deposited with the regular (RP) or high-purity 8 wt% yttria stabilized zirconia (HP-YSZ) feedstock. The purity of the feedstock powder used for preparing the buffer layer affected the fracture behavior, showing a better thermal durability for the TBCs with the HP-YSZ in both frequency test conditions. A finite element model is developed, which takes creep effect into account due to thermal cycling. The model shows the high stresses at the interfaces between different layers due to differential thermal expansion. The failure mechanisms of YGYZ-based TBCs in TGMF test are also proposed. The vertical cracks are preferentially created, and then the vertical and horizontal cracks will be propagated when the vertical cracks are impeded by pores and micro-cracks

The 1st International Joint Mini-Symposium on Advanced Coatings between Indiana University-Purdue University Indianapolis and Changwon National University: Preface

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

Thermal properties of La2Zr2O7 double-layer thermal barrier coatings

La2Zr2O7 is a promising thermal barrier coating (TBC) material. In this work, La2Zr2O7 and 8YSZ-layered TBC systems were fabricated. Thermal properties such as thermal conductivity and coefficient of thermal expansion were investigated. Furnace heat treatment and jet engine thermal shock (JETS) tests were also conducted. The thermal conductivities of porous La2Zr2O7 single-layer coatings are 0.50–0.66 W m−1 °C−1 at the temperature range from 100 to 900°C, which are 30–40% lower than the 8YSZ coatings. The coefficients of thermal expansion of La2Zr2O7 coatings are about 9–10 × 10−6 °C−1 at the temperature range from 200 to 1200°C, which are close to those of 8YSZ at low temperature range and about 10% lower than 8YSZ at high temperature range. Double-layer porous 8YSZ plus La2Zr2O7 coatings show a better performance in thermal cycling experiments. It is likely because porous 8YSZ serves as a buffer layer to release stress

Extrusion-Based 3D Printing of Molecular Sieve Zeolite for Gas Adsorption Applications

Extrusion based 3D printing is one of the emerging additive manufacturing technologies used for printing range of materials from metal to ceramics. In this study, we developed a customized 3D printer based on extrusion freeform fabrication technique, such as slurry deposition, for 3D printing of different molecular sieve zeolite monoliths like 3A, 4A, 5A and 13X to evaluate their performance in gas adsorption. The physical and structural properties of 3D printed zeolite monoliths will be characterized along with the gas adsorption performance. The Brunauer–Emmett–Teller (BET) test of 3D printed samples will be performed for calculation of the surface area, which will give us the capacity of gas absorption into 3D printed zeolite. The BET surface area test showed good results for Zeolite 13X compared to available literature. The surface area calculated for 3D – printed Zeolite 13X was 767m2/g and available literature showed 498 m2/g for 3D – printed Zeolite 13X. The microhardness values of 3D – printed Zeolite samples were measured using a Vicker hardness tester. The hardness value of the 3D - printed Zeolite samples increased from 8.3 ± 2 to 12.5 ± 3 HV 0.05 for Zeolite 13X, 3.3 ± 1 to 7.3 ± 1 HV 0.05 for Zeolite 3A, 4.3 ± 2 to 7.5 ± 2 HV 0.05 for Zeolite 4A, 7.4 ± 1 to 14.0 ± 0.5 HV 0.05 for Zeolite 5A, before and after sintering process, respectively. The SEM analysis was performed for 3D printed samples before and after sintering to evaluate their structural properties. The SEM analysis reveals that all 3D – printed Zeolite samples retained their microstructure after slurry preparation and also after the sintering process. The porous nature of 3D – printed Zeolite walls was retained after the sintering process

Molecular Dynamics Simulation of Electrical Resistivity in Sintering Process of Nanoparticle Silver Inks

A molecular dynamics (MD) model is developed to simulate low temperature sintering of silver nanoparticles and resultant resistivity. Due to the high surface to volume ratio, nanoparticle silver inks can sinter at low thermal curing temperatures, which are used in intense pulsed light (IPL) sintering process. In this study, the configurational change of nanoparticle silver during sintering is studied using the MD model. Then the resultant electric resistivity is calculated using the Reimann-Weber formula. The simulation results show that the resistivity decreases rapidly in the initial sintering stage, due to the fast neck formation and growth. Additionally, the predicted temperature-dependent resistivity evolutions are in good agreement with both experimental measurements and analytical sintering model, indicating that the resistivity decreases with increasing sintering temperature. The model provides a design tool for optimizing IPL process

STUDY OF THE THERMAL AND MECHANICAL PROPERTIES OF LA2ZR2O7 USING FIRST PRINCIPLE METHOD

poster abstractAs an advanced thermal barrier coating, Lanthanum zirconia (La2Zr2O7) has been studied in this paper using first principle calculations. La2Zr2O7 crystal bulk was used in this calculation. The lattice parameter, mechanical and thermal properies of La2Zr2O7 were investigated by means of density functional theory (DFT). Hydrostatic pressure-dependent elasticity constant, bulk modulus were calculated. The thermal conductivity was calculated based on fick’s law using a 20 layers supercell. La2Zr2O7 coating samples were spraied by APS equipment, the coating samples were identified by XRD and observed by optical microscope. The thermal effect of Ce doping of the La2Zr2O7 were studied by ab initial calculations. The calculated properties have considerable good agreement with others experimental and calculation results

Microstructural non-uniformity and mechanical property of air plasma-sprayed dense lanthanum zirconate thermal barrier coating

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

Crack-Resistance Behavior of an Encapsulated, Healing Agent Embedded Buffer Layer on Self-Healing Thermal Barrier Coatings

In this work, a novel thermal barrier coating (TBC) system is proposed that embeds silicon particles in coating as a crack-healing agent. The healing agent is encapsulated to avoid unintended reactions and premature oxidation. Thermal durability of the developed TBCs is evaluated through cyclic thermal fatigue and jet engine thermal shock tests. Moreover, artificial cracks are introduced into the buffer layer’s cross section using a microhardness indentation method. Then, the indented TBC specimens are subject to heat treatment to investigate their crack-resisting behavior in detail. The TBC specimens with the embedded healing agents exhibit a relatively better thermal fatigue resistance than the conventional TBCs. The encapsulated healing agent protects rapid large crack openings under thermal shock conditions. Different crack-resisting behaviors and mechanisms are proposed depending on the embedding healing agents