IU Indianapolis ScholarWorks :: Browsing by Author "Jung, Yeon-Gil"

Browsing by Author "Jung, Yeon-Gil"

Now showing 1 - 10 of 42

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.
Additive Manufacturing of Metallic Materials: A Review
(Springer, 2017) Zhang, Yi; Wu, Linmin; Guo, Xingye; Kane, Stephen; Deng, Yifan; Jung, Yeon-Gil; Lee, Je-Hyun; Zhang, Jing; Mechanical Engineering, School of Engineering and Technology
In this review article, the latest developments of the four most common additive manufacturing methods for metallic materials are reviewed, including powder bed fusion, direct energy deposition, binder jetting, and sheet lamination. In addition to the process principles, the microstructures and mechanical properties of AM-fabricated parts are comprehensively compared and evaluated. Finally, several future research directions are suggested.
Atomistic Modeling of Anisotropic Mechanical Properties of Lanthanum Zirconate Nanocystal
(Elsevier, 2021-02) Guo, Xingye; Zhang, Jian; Park, Hye-Yeong; Jung, Yeon-Gil; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
Lanthanum zirconate (La2Zr2O7, or LZ) has been widely recognized as a promising candidate material for thermal barrier coating (TBC) applications since it has low thermal conductivity, high-temperature phase stability, and low sintering activity. However, the mechanical properties of LZ crystal have not been fully understood, which hinders it from future applications. In this work, atomistic simulations were performed to study the anisotropic mechanical properties of LZ crystal. Using both the first principles and molecular dynamics (MD) calculations, uniaxial tensile tests of LZ crystal in [001], [011], and [111] directions were simulated. The stress-strain curves of the tensile tests were calculated, and the ultimate tensile strength and toughness were derived. The Young's moduli in [001], [011], and [111] directions were calculated using both the stress-strain curves and an analytical method for small deformation. Additionally, shear stress-strain curves in {111}<110> and {111}<112> directions were investigated using both the first principles calculations and the MD method. Results show that Young's modulus of LZ crystal is highly anisotropic. The crystal has the highest Young's modulus in [111] direction, and {111}<112> direction is the favorable slip system during shear deformations.
Characterization of Microstructure and Mechanical Properties of Direct Metal Laser Sintered 15–5 PH1 Stainless Steel Powders and Components
(Springer, 2016) Zhang, Jing; Zhang, Yi; Guo, Xingye; Lee, Weng Hoh; Hu, Bin; Lu, Zhe; Jung, Yeon-Gil; Lee, Je-Hyun; Department of Mechanical Engineering, School of Engineering and Technology
15–5 PH1 stainless steel powder is one of the common materials used for the DMLS process. In this study, both the powder and parts fabricated via DMLS have been characterized. The microstructure and elemental composition have been examined. The microhardness and surface roughness have also been measured. The results show that most powder particle are in spherical with a particle size of 5 ~ 60 μm. Chemical compositions of the powder compare well with the literature data. The thickness of rough surface is about 1 μm. The measured Rockwell hardness is HRC 42.9±0.3, which is also in good agreement with literature.
Crack-Growth Behavior in Thermal Barrier Coatings with Cyclic Thermal Exposure
(MDPI, 2019-06) Song, Dowon; Song, Taeseup; Paik, Ungyu; Lyu, Guanlin; Jung, Yeon-Gil; Choi, Baig-Gyu; Kim, In-Soo; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
Crack-growth behavior in yttria-stabilized zirconia-based thermal barrier coatings (TBCs) is investigated through a cyclic thermal fatigue (CTF) test to understand TBCs’ failure mechanisms. Initial cracks were introduced on the coatings’ top surface and cross section using the micro-indentation technique. The results show that crack length in the surface-cracked TBCs grew parabolically with the number of cycles in the CTF test. Failure in the surface-cracked TBC was dependent on the initial crack length formed with different loading levels, suggesting the existence of a threshold surface crack length. For the cross section, the horizontal crack length increased in a similar manner as observed in the surface. By contrast, in the vertical direction, the crack did not grow very much with CTF testing. An analytical model is proposed to explain the experimentally-observed crack-growth behavior.
Crack-Resistance Behavior of an Encapsulated, Healing Agent Embedded Buffer Layer on Self-Healing Thermal Barrier Coatings
(MDPI, 2019) Song, Dowon; Song, Taeseup; Paik, Ungyu; Lyu, Guanlin; Jung, Yeon-Gil; Choi, Baig-Gyu; Kim, In-Soo; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
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.
Density Functional Theory Study of Gas Adsorption on Lanthanum Zirconate Nanostructured Coating Surface
(Office of the Vice Chancellor for Research, 2015-04-17) Guo, Xingye; Zhang, Jing; Jung, Yeon-Gil; Li, Li; Knapp, James
Lanthanum zirconate (La2Zr2O7) is a typical pyrochlore ceramic material, which can be used as thermal barrier coating (TBC). However, it may deteriorate by oxidizing and corrosive gases, such as CO2, O2, SO2 and CH4 during its operation process at elevated temperatures. This work investigates CO2, O2, SO2 and CH4 gas adsorption mechanism on La2Zr2O7 nanostructured coating surfaces using the density functional theory (DFT) calculations. La2Zr2O7 surface energies on (001), (011) and (111) planes were calculated. Results show the most thermodynamically stable surfaces of La2Zr2O7 are (011) and (111) planes, due to their low surface energies. Adsorption energies of CO2, O2, SO2 and CH4 on (001), (011) and (111) planes in different sites were studied as well. The results show the most favorable gas adsorption sites for CO2, O2, SO2 and CH4 occur at 3-fold and 4-fold sites. The most favorable gas adsorption plane for CO2, O2, SO2 and CH4 is (111) plane.
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 thermal cycling frequency on the durability of Yb-Gd-Y-based thermal barrier coatings
(Elsevier, 2019-04) Lyu, Guanlin; Choi, Baig-Gyu; Lu, Zhe; Park, Hyeon-Myeong; Jung, Yeon-Gil; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
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.
Experimental and Modeling Studies of Bond Coat Species Effect on Microstructure Evolution in EB-PVD Thermal Barrier Coatings in Cyclic Thermal Environments
(MDPI, 2019) Lu, Zhe; Lyu, Guanlin; Gulhane, Abhilash; Park, Hyeon-Myeong; Kim, Jun Seong; Jung, Yeon-Gil; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
In this work, the effects of bond coat species on the thermal barrier coating (TBC) microstructure are investigated under thermal cyclic conditions. The TBC samples are prepared by electron beam-physical vapor deposition with two species of bond coats prepared by either air-plasma spray (APS) or high-velocity oxygen fuel (HVOF) methods. The TBC samples are evaluated in a variety of thermal cyclic conditions, including flame thermal fatigue (FTF), cyclic furnace thermal fatigue (CFTF), and thermal shock (TS) tests. In FTF test, the interface microstructures of TBC samples show a sound condition without any delamination or cracking. In CFTF and TS tests, the TBCs with the HVOF bond coat demonstrate better thermal durability than that by APS. In parallel with the experiments, a finite element (FE) model is developed. Using a transient thermal analysis, the high-temperature creep-fatigue behavior of the TBC samples is simulated similar to the conditions used in CFTF test. The FE simulation predicts a lower equivalent stress at the interface between the top coat and bond coat in bond coat prepared using HVOF compared with APS, suggesting a longer cyclic life of the coating with the HVOF bond coat, which is consistent with the experimental observation.

Browsing by Author "Jung, Yeon-Gil"

Results Per Page

Sort Options