• Journal of the Optical Society of Korea
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• v.18 no.3
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• pp.256-260
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• 2014

Columnar-structured cesium iodide (CsI) scintillators doped with thallium (Tl) are frequently used as x-ray converters in medical and industrial imaging. In this study we investigated the imaging characteristics of CsI:Tl films with various reflective layers-aluminum (Al), chromium (Cr), and titanium dioxide ($TiO_2$) powder-coated on glass substrates. We used two effusion-cell sources in a thermal evaporator system to fabricate CsI:Tl films on substrates. The scintillators were observed via scanning electron microscopy (SEM), and scintillation characteristics were evaluated on the basis of the emission spectrum, light output, light response to x-ray dose, modulation transfer function (MTF), and x-ray images. Compared to control films without a reflective layer, CsI:Tl films with reflective layers showed better sensitivity and light collection efficiency, and the film with a $TiO_2$ reflective layer showed the best properties.

• Korean Journal of Metals and Materials
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• v.46 no.3
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• pp.125-130
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• 2008

Conventional plasma carburizing or nitriding for austenitic stainless steels results in a degradation of corrosion resistance. However, a low temperature plasma surface treatment can improve surface hardness without deteriorating the corrosion resistance. The 2-step low temperature plasma processes (the combined carburizing and post nitriding) offers the increase of both surface hardness and thickness of hardened layer and corrosion resistance than the individually processed low temperature nitriding and low temperature carburizing techniques. In the present paper, attempts have been made to investigate the influence of the introduction of Ar gas (0~20%) in nitriding atmosphere during low temperature plasma nitriding at $370^{\circ}C$ after low temperature plasma carburizing at $470^{\circ}C$. All treated specimens exhibited the increase of the surface hardness with increasing Ar level in the atmosphere and the surface hardness value reached up to 1050 HV0.1, greater than 750 $HV_{0.1}$ in the carburized state. The expanded austenite phase (${\gamma}_N$) was observed on the most of the treated surfaces. The thickness of the ${\gamma}_N$ layer reached about $7{\mu}m$ for the specimen treated in the nitriding atmosphere containing 20% Ar. In case of 10% Ar containing atmosphere, the corrosion resistance was significantly enhanced than untreated austenitic stainless steels, whilst 20% Ar level in the atmosphere caused to form CrN in the N-enriched layer (${\gamma}_N$), which led to the degradation of corrosion resistance compared with untreated austenitic stainless steels.

• Korean Journal of Metals and Materials
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• v.46 no.11
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• pp.737-746
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• 2008

Mechanisms of sticking phenomena occurring during hot rolling of a modified STS 430J1L ferritic stainless steel have been investigated in this study by using a pilot-plant-scale rolling machine. As the rolling pass proceeds, the Fe-Cr oxide layer formed in a reheating furnace is destroyed, and the destroyed oxides penetrate into the rolled steel to form a thin oxide layer on the surface region. The sticking does not occur on the surface region containing oxides, whereas it occurs on the surface region without oxides by the separation of the rolled steel at high temperatures. This indicates that the resistance to sticking increases by the increase in the surface hardness when a considerable amount of oxides are formed on the surface region, and that the sticking can be evaluated by the volume fraction and distribution of oxides formed on the surface region. The lubrication and the increase of the rolling speed and rolling temperature beneficially affect to the resistance to sticking because they accelerate the formation of oxides on the steel surface region. In order to prevent or minimize the sticking, thus, it is suggested to increase the thickness of the oxide layer formed in the reheating furnace and to homogeneously distribute oxides along the surface region by controlling the hot-rolling process.

• Journal of Powder Materials
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• v.29 no.3
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• pp.240-246
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• 2022

Novel Ni- and Fe-based alloys are developed to impart improved mechanical properties and corrosion resistance. The designed alloys are manufactured as a powder and deposited on a steel substrate using a high-velocity oxygen-fuel process. The coating layer demonstrates good corrosion resistance, and the thus-formed passive film is beneficial because of the Cr contained in the alloy system. Furthermore, during low-temperature heat treatment, factors that deteriorate the properties and which may arise during high-temperature heat treatment, are avoided. For the heattreated coating layers, the hardness increases by up to 32% and the corrosion resistance improves. The influence of the heat treatment is investigated through various methods and is considered to enhance the mechanical properties and corrosion resistance of the coating layer.

• Journal of Welding and Joining
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• v.32 no.4
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• pp.34-38
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• 2014

Carburizing treatments are the important way to developing fatigue strength and wear resistance. It is well known that the case depth is one of the most significant parameters determining fatigue strength. In this study, 3-point bending fatigue test was conducted to evaluate fatigue strength for the carburized depth with 18CrNiMo7-6 steel. As a result, fatigue strength increased with effective case depth decreased. It is shown that hardness in case hardened layer played principal role in the fatigue strength.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.140-143
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• 2003

The drawbead is an important part in sheet metal forming for automotive part and its effect is affected by various process parameters. Therefore in this study, drawbead friction test was performed at various process parameters - panels (cold rolled and galvanized sheet steel), lubricants (having three different viscosities), bead materials(steel, iron) and surface treatment of bead (Cr plating). Circular shape bead has been used for the test. The results show that friction and drawing characteristics were mainly influenced by the nature of zinc coating, viscosity of lubricants, surface treatment of a bead and hardness of coated layer.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.10 s.253
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• pp.1179-1186
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• 2006

This paper was designed to assess the adhesive properties of hard coatings on non-nitrided and nitrided various tool steels. Estimations of adhesion were done to scratch test which is mainly used in hard coating. The critical load$(L_c)$ between coating and substrate is defined through analysis of frictional load vs. normal load curve, signals of acoustic emission and optical observations. Coatings employed in this study are TiN, CrN and TiAlN, tools as substrates are STD11, STD61 and SKH51. It was classified to substrates with/without intermediate nitrided layer and hard coatings on substrate were deposited by arc PVD. Results showed that harder substrates and coatings give higher values of critical loads.

• Journal of Powder Materials
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• v.4 no.4
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• pp.252-257
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• 1997

Cu-brazed layer between the sintered-cam(Fe-5Cr-lMo-0.5P-2.5C, wt%) and seamless steelpipe(0.25-0.35C, 0.3-1.0 Mn, bal Fe, wt%) in the camshaft shows a columnar structure of $\gamma$-phase growing from the steel pipe. Liquid phase sintered 60Fe-40Cu alloys are carburized to simulate the brazing process giving rise to the columnar growth. Liquid film migrations and columnar growth of $\gamma$-grains are observed in the carburized regions. The $\gamma$-grains grow in the same direction as the C-diffusion. Fe-solubility in the liquid of carburized region is higher than in the uncarburized by about 0.3 at%. The columnar growth is driven by the gradient of the supersaturated Fe-solute in the liquid between two adjacent $\gamma$-grains.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.5
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• pp.61-66
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• 1997

In this paper we report the fabrication of an InGaAs metal-semiconductor-metal (MSM) photodiode(PD) which an InAlAs barrier enhancement layer that has very low dark current and high speed chracteristics. The detector using Cr/Au schottky metal fingers with 4um spacing on a large active area of 300*300um$^{2}$ offers a low dark current of 38nA at 10V, a low capacitance of 0.8pF, and a high 3-dB bandwidth of 2.4 GHz. To our knowledge, these characteristics are better than any previously published results obtained from large area InGaAs MSM PD's. The RC equivalent model and frequency domain current response model considering transit time were also used to analyze the frequency characteristic of the fabricated device.

• Journal of information and communication convergence engineering
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• v.5 no.4
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• pp.320-323
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• 2007

This paper presents the resonance characteristics of the ZnO-based FBAR devices with multilayered Bragg reflectors with Cr adhesion layer inserted between $SiO_2$ and W layers. Due to the post- annealing, the return loss ($S_{11}$) and series/parallel quality factor are significantly improved when compared with the non-post annealing. This post-annealing method seems to be a very efficient way to improve the resonance characteristics of FBAR devices.