• Journal of the Korean Society for Heat Treatment
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• v.32 no.3
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• pp.113-117
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• 2019

The effects of severe plastic deformation and heat treatment on the mechanical properties of Al 5052 and 6005 alloys were investigated using the metallurgical technique and nano-indentation technique in nano-surface region. Equal channel angular pressing (ECAP) was used to apply severe plastic deformation to the aluminum alloys in order to obtain fine grain sized materials. The elastic modulus was measured and interpreted in relation to the metallurgical observation. The elastic modulus increased after ECAP process due to evolution of the fine grains. However, the elastic modulus decreased after heat treatment due to generation of coarsened precipitates on the grain boundaries.

• Proceedings of the Materials Research Society of Korea Conference
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• 2002.11a
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• pp.112-112
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• 2002

• Journal of the Korean Ceramic Society
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• v.45 no.9
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• pp.549-555
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• 2008

The thermal barrier coating must withstand erosion when subjected to flowing gas and should also maintain good stability and mechanical properties while it must also protect the turbine component from high temperature, hot corrosion, creep, and oxidation during operation. In this study we investigated the influence of subsurface layer, $Al_2O_3$ or NiCrCoAIY bond coat layer, on the indentation damage behavior of YSZ thermal barrier coating layers deposited by electron beam physical vapor deposition (EB-PVD). The bond coat is deposited using different process such as air plasma spray (APS) or spray of high velocity oxygen fuel (HVOF) and the thickness is varied. Hertzian indentation technique is used to induce micro damages on the coated layer. The stress-strain behaviors are characterized by results of the indentation tests.

• Journal of the Korean Institute of Gas
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• v.12 no.2
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• pp.92-98
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• 2008

A combination of the instrumented indentation and 3D morphology measurement has been tried in order to perform a real-time property measurement of degraded materials in gas pipelines; three-dimensional indent morphologies were recorded using a reflective laser scanner after a series of insturmented indentations on three metallic specimens. Dimensions of the permanent deformation zone and contact boundary were analyzed from the cross-sectional profile over an remnant indent and used for estimating yield strength and hardness, respectively. Estimated yield strength was comparable with that from uniaxial tensile test and actual hardness implying material pile-up effects was lower than the calculated value from indentation curve by $20{\sim}30%$. It means that this 3D image analysis can explain the material pile-up effects on the contact properties. Additionally, a combined system of indentation and laser sensor was newly designed by modifying a shape of the indentation loading fixture.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.1
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• pp.53-59
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• 2014

Because a molten steel carrier is used in high-temperature and corrosive environments, erosion and corrosion decrease the thickness of the structure and expand the vent hole for emitting gas generated from refractory bricks. This increases the stress throughout the structure and introduces a significant stress concentration around the vent hole. In addition, the high-temperature environment degrades mechanical properties such as the yield and tensile strengths. These problems seriously affect the safety of the structure. In this study, the safety of a 10-year-old structure was evaluated by analyzing the stress distribution and measuring the mechanical properties of the structure. The mechanical properties were directly measured on the structure surface using the instrument indentation technique.

• Corrosion Science and Technology
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• v.7 no.3
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• pp.145-151
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• 2008

Material degradation such as high temperature oxidation of metallic material is a severe problem in energy generation systems or manufacturing industries. The metallic materials are oxidized to form oxide films in high temperature environments. The oxide films act as diffusion barriers of oxygen and metal ions and thereafter decrease oxidation rates of metals. The metal oxidation is, however, accelerated by mechanical fracture and spalling of the oxide films caused by thermal stresses by repetition of temperature change, vibration and by the impact of solid particles. It is therefore very important to investigate mechanical properties and adhesion of oxide films in high temperature environments, as well as the properties in a room temperature environment. The oxidation tests were conducted for Ni and Ni-Co alloy under high temperature corrosive environments. The hardness distributions against the indentation depth from the top surface were examined at room temperature. Dynamic indentation tests were performed on Ni oxide films formed on Ni surfaces at room and high temperature to observe fractures or cracks generated around impact craters. As a result, it was found that the mechanical property as hardness of the oxide films were different between Ni and Ni-Co alloy, and between room and high temperatures, and that the adhesion of Ni oxide films was relatively stronger than that of Co oxide films.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.368-369
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• 2008

This paper describes the mechanical properties of poly(polycrystalline) 3C-SiC thin film with various doping concentration, in which poly 3C-SiC thin film's mechanical properties according to the n-doping concentration 1%$(9.2\times10^{15}cm^{-3})$, 3%$(5.2\times10^{17}cm^{-3})$, and 5%$(6.8\times10^{17}cm^{-3})$ respectively was measured by nano indentation. In the case of $9.2\times10^{15}^{-3}$ n-doping concentration, Young's Modulus and hardness were obtained as 270 GPa and 30 GPa, respectively. When the surface roughness according to n-doping concentrations was investigated by AFM(atomic force microscope), the roughness of poly 3C-SiC thin film doped by 5% concentration was 15 nm, which is also the best of them.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.63-68
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• 2005

The nanoindentation technique is widely used to investigate the mechanical properties of nano-microscale materials. The nanoindentation method for assessing mechanical properties at low loads and shallow depths is already well established fur the characterization of thin films as well as bulk materials. In this study, we evaluated residual stress in DLC and Au thin films usign nanoindentation technique with a new stress-relaxation model. Moreover, We suggest a composite hardness equation and quantify the magnitude of hardness increase by using an equation based on the interface hardness and the interface thickness, derived by comparing results derived from this equation and those determined in nanoindentation tests. Finally, We present an indentation size effect (ISE) model that extends the available contact depth for ISE application down to several tens of nanometers by considering the tip bluntness effect.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.36 no.2
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• pp.127-136
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• 2020

Prism compressive strength is the most influential parameter to evaluate the seismic performance of non-structural concrete brick masonry walls, and is affected by the practice and workmanship of masonry workers. This study experimentally investigates the influence of workmanship on prism compressive strength throughout the compressive test with prism specimens constructed according to masonry workmanship. To do this, the workmanship is categorized into good, fair, and poor conditions which are statistically evaluated with thickness and indentation depth of bed-joints. Then, the effect of workmanship on the structural properties of masonry prisms is evaluated by investigating relations between properties such as their compressive strength, elastic modulus and numerical parameters such as thickness, filling of bed-joints. This study demonstrates that the indentation depth is more important parameter for structural properties of masonry prisms and masonry prisms with loss in bed-joint area less than of 7% can be in fair condition.

• Journal of Ceramic Processing Research
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• v.19 no.5
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• pp.394-400
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• 2018

The current work investigates the effects of nucleation heat treatments, on the microstructure and mechanical properties of a novel silicate glass in $Li_2O-BaO-SiO_2$ system with 1 mol% $P_2O_5$ as nucleating agent. As-cast glass was exposed to nucleation heat treatments at $490-550^{\circ}C$ for 1-3 h. The microstructural examination was performed by SEM/EDS. The highest Vickers microhardness was determined to be 650 Hv for the sample heat treated at $550^{\circ}C$ for 1 h. The increase in the nucleation time also affected Vickers microhardness and the highest one was determined to be 600 Hv after nucleation for 3 h. The fracture toughness, $K_{IC}$ reached $2.51MPa.m^{1/2}$ after nucleation at $550^{\circ}C$ for 1 h. The nucleation temperatures had a more pronounced effect on the fracture toughnesses in comparison to nucleation times. The indentation toughness data was used to determine Weibull parameters from Ln ln [1/(1-P)]-$lnK_{IC}$ plots. Weibull modulus, m of the samples nucleated at 500, 510, 530, $550^{\circ}C$ for 1h. and $540^{\circ}C$ for 2 h. were determined similarly to be 3.8, 3.5, 4.7 and 3.9, respectively. The rest of the samples indicated higher Weibull moduli, which may be attributed to the formations of microcracks due to the mismatch in between newly formed crystals and remaining glassy matrix.