• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.1
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• pp.132-136
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• 1999

Mechanical alloying (MA) by ball mill of $Fe_{30}Cr_{70}$ elemental powders was carried out under the nitrogen gas atmosphere. Amorphization has been observed in this case, while MA under an inert argon gas atmosphere produces the bcc solid solution. The DSC spectrum for the mechanically alloyed $(Fe_{30}Cr_{70})_{0.85}N_{0.15)$powders exhibits a sharp exothermic peak due to crystallization at about $550^{\circ}C$. Structural transformation from the bcc crystalline to amorphous states was observed through X-ray and neutron diffractions. During amorphization process the octahedral unit, which is typical of a polyhedron formed in any crystal structures, was preferentially destroyed and transformed into the tetrahedral unit. Futhermore, neutron diffraction measurements revealed that a nitrogen atom is situated at a center of the tetrahedron formed by metal atoms.

• Journal of the Institute of Convergence Signal Processing
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• v.9 no.2
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• pp.146-153
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• 2008

Integrated humidity sensor system with two stages operational amplifier has been designed and fabricated by $0.8{\mu}m$ analog mixed CMOS technology. The system (28 pin and $2mm{\times}4mm$) consisted of Wheatstone-bridge type humidity sensor, resistive type humidity sensor, temperature sensors and operational amplifier for signal amplification and process in one chip. The poly-nitride etch stop process has been tried to form the sensing area as well as trench in a standard CMOS process. This modified technique did not affect the CMOS devices in their essential characteristics and gave an allowance to fabricate the system on same chip by standard process. The operational amplifier showed the stable operation so that unity gain bandwidth was more than 5.46 MHz and slew rate was more than 10 V/uS, respectively. The drain current of n-channel humidity sensitive field effect transistor (HUSFET) increased from 0.54 mA to 0.68 mA as the relative humidity increased from 10 to 70 %RH.

• Journal of the Korean institute of surface engineering
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• v.54 no.5
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• pp.267-277
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• 2021

Nitriding layers developed during gaseous nitriding of AISI4115 steels for the application of steel bushing part were investigated. The compound layer thickness of about 10㎛, 0.3mm of case depth under the same conditions, and conventional nitriding, nitrocarburizing, and controlled nitriding were performed in three methods. In the controlled nitriding, K_N was controlled by measuring the hydrogen partial pressure. The nitrided samples were analyzed by micro Vickers hardness test, optical microscopy and scanning electron microscopy. The phases of compound layer were identified by X-ray diffraction and electron backscatter diffraction. The controlled nitriding specimen indicated the highest surface hardness of about 860 HV_0.1. The compound layer of the conventional nitriding and nitrocarburizing specimen was formed with about 46% porous layer and 𝜺 + 𝜸' phase, and about 13% porous layer and about 80% 𝜸' phase were formed on the controlled nitriding specimen. As a result of the Ball-on-disk wear test, the worn mass loss of ball performed on the surface of the controlled nitriding specimen was the largest. The controlled nitriding specimen had the highest surface hardness due to the lowest porous percentage of compound layer, which improved the wear resistance.

• Journal of the Korean Society for Heat Treatment
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• v.37 no.2
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• pp.49-57
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• 2024

We investigated the changes in microstructure and surface roughness of the compound layer of GC250D gray cast iron, commonly used in brake discs, during gas nitriding. The gas atmosphere of the nitriding process was controlled with a hydrogen partial pressure of 49.5%, and the process was conducted at a nitriding temperature of 520℃ with various process times. As the nitriding process time of the GC250D material increased, both the depth of hardening and the thickness of the compound layer increased, with a maximum surface hardness of approximately 1265 HV_0.1 was measured. Additionally, the surface roughness increased with the process time. Phase analysis of the compound layer revealed an increase in the proportion of the γ' phase as the nitriding process time increased. Changes in the formation of the compound layer were observed depending on the orientation of graphite within the material, leading to the formation of wedges. Therefore, the increase in surface roughness appears to be attributed to the uneven compounds, the expansion of the compound layer and wedges formed on the surface during the nitriding process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.18-18
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• 2009

최근 다양하게 연구되고 있는 무분극(nonpolar) 갈륨질화물(GaN) 소재는 자발분극(spontaneous polarization) 및 압전분극(piezoelectric polarization) 등이 발생하지 않아 높은 내부양자효율의 확보가 가능하며, 이러한 장점을 바탕으로 고효율 특성을 갖는 발광다이오드(light-emitting diode) 및 고속 전자소자 등으로의 적용을 위한 연구가 활발히 수행 중 이다. 하지만, 무분극 GaN LED의 구현 시, GaN 박막의 비등방성 성장으로 인한 박막의 막질 저하와 함께 표면에 혼재하는 Ga층과 N층에서 기인되는 절연층의 생성으로 인한 오믹전극 형성의 어려움이 대두되고 있다. 따라서, 고효율의 무분극 GaN LED 구현을 위해서는 무분극 GaN층의 질소층 제거를 위한 표면처리 공정과 더불어 금속/무분극 GaN층 간 발생되는 쇼트키 장벽층의 높이(Schottky barrier height)를 제어하는 연구가 선행되어야 한다. 본 논문에서는 무분극 GaN LED 적용을 위한 n-형 전극물질 및 오믹조건 구현을 위한 금속/무분극 GaN층간 SBH의 제어방법에 대한 연구를 수행하였다.

• Tribology and Lubricants
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• v.13 no.1
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• pp.42-52
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• 1997

This paper deals with wear characteristics of ion-nitrided metal theoretically and experimentally in order to analysis of wear phenomena. Wear tests show that compound layer of ion-nitrided metal reduces wear rate when the applied wear load is mall. However, as th load becomes large, the existence of compound layer tends to increase wear rate. The residual stress at the surface of ion-nitrided metal is measured, and the internal stress distribution is calculated when the normal and tangential forces are applied to the surface of metal. Compressive residual stress is largeest at the compound layer, and decreases as the depth from the surface increases. Calculation shows that the maximum stress exists at a certain depth from the surface when normal and tangential force are applied, and that the larger the wear load is the deeper the location of maximum stress becomes. In the analysis, it is found that under small applied wear load the critical depth, where voids and cracks may be created and propagated, is located at the compound layer, as the adhesive wear, where hardness is an important factor, is created the existence of compound layer reduces the amount of wear. When the load becomes large the critical depth is located below the compound layer, and delamination, which may be explained by surface deformation, crack nucleation and propagation, is created, and the existence of compound layer increases wear rate.

• Journal of Welding and Joining
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• v.10 no.1
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• pp.12-19
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• 1992

용접능률의 향상을 위한 대입열용접법의 적용은 과도한 입열량으로 인하여 용접부의 인성이 저 하한다는 점에서 그 적용에 주의를 요한다. 본 보에서는 대입열용접시 열영향부의 인성 저하의 원인과 그 대책을 강재의 측면에서 검토하였다. 고장력강을 용접하면 입열량이 증가함에 따라 오스테나이트 결정립이 조대화되고 상부 베이나이트와 도상 마르텐사이트가 생성되어 인성이 저하한다. 그 대책으로서는 용접 열싸이클과정중 안정한 질화물, 산화물등을 모재에 미세분산시켜 오스테나이트 결정립 성장을 억제하고, 페라이트, 펄라이트 변태를 촉진시킨다. 이러한 석출물의 형성을 위해서는 주로 Ti, Ca, REM, B등의 합금원소가 이용된다. 소입성이 높은 주질고장력 강에서는 석출물의 분산에 의한 페라이트의 변태 촉진 보다는 Mn, Ni, Cr, Mo, V등의 합금원 소를 첨가하여 소입성을 높여 인성이 우수한 하부 베이나이트 조직을 형성하든가, 탄소량을 저 감시켜 도상 마르텐사이트의 생성을 억제하므로서 인성을 확보한다. 현재 국내에서 제조되고 있는 대입열용접용강중 인장강도 50kgf/mm$^{2}$급강은 기본적으로 용접부 인성이 우수한 TMCP법으로 제조되며, Ti등을 첨가하여 석출물의 효과를 이용하고 N을 억제하여 기지의 인 성을 향상시키는 등의 방법을 병용하고 있다. 인장강도 60kgf/mm$^{2}$ 급강은 조질처리에 의하여 제조되며, 50kgf/mm$^{2}$급강과 같이 Ti, B등의 첨가에 의한 석출물의 효과를 이용 하고 있다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.1
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• pp.39-44
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• 2014

Silicon nitride thin film deposited with Plasma Enhanced Chemical Vapor Deposition was treated by a nitrogen plasma generated by Inductively Coupled Plasma at room temperature. The treatment was investigated by Fourier Transform Infrared Spectroscopy and Atomic Force Microscopy on the surface at various RF source powers at two RF bias powers. The amount of hydrogen was reduced and the surface roughness of the films was decreased remarkably after the plasma treatment. In order to understand the causes, we analyzed the plasma diagnostics by Optical Emission Spectroscopy and Double Langmuir Probe. Based on these analysis results, we show that the nitrogen plasma treatment was effective in the improving of the properties silicon nitride thin film for flexible display.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.567-572
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• 2001

In order to investigate the fracture behaviors(penetration modes) and resistance to penetration during ballistic impact of Titanium alloy laminates and nitrified Titanium alloy laminates which were treated by PVD(Physical Vapor Deposition) method, ballistic tests were conducted. Evaporation, sputtering, and ion plating are three kinds of PVD method. In this research, Ion plating was used to achieve higher surface hardness and surface hardness test were conducted using a Micro vicker's hardness tester. Resistance to penetration is determined by the protection ballistic limit($V_{50}$), a statistical velocity with 50% probability for complete penetration. Fracture behaviors and ballistic tolerance, described by penetration modes, are respectfully observed at and above ballistic limit velocities, as a result of $V_{50}$ test and Projectile Through Plates (PTP) test methods. PTP tests were conducted with $0^{\circ}$ obliquity at room temperature using 5.56mm ball projectile. $V_{50}$ test with $0^{\circ}$ obliquity at room temperature were conducted with projectiles that were able to achieve near or complete penetration during PTP tests. Surface hardness, resistance to penetration, and penetration modes of Titanium alloy laminates are compared to those of nitrified Titanium alloy laminates.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.6
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• pp.361-367
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• 2009

The two-step gas nitriding was adopted to increase the depth of surface hardening in 3%Cr-Mo-V steel. The two-step gas nitriding consisted of Step I; $520^{\circ}C{\times}20\;hrs$ and Step II; $550^{\circ}{\times}70\;hrs$. The layer of two-step gas nitriding showed better uniformity and deeper nitriding layer than one-step gas-nitriding layer. The maximum surface hardness showed the value of 850 Hv. The maximum depth of nitrogen permeation showed $750\;{\mu}m$ (350 Hv). X-ray diffraction analysis showed that compound layer was mainly consisted of CrN and $\varepsilon-Fe_3N$ phases. These phases were presumed contributing to surface hardening and wear resistance. However, the corrosion resistance of gas-nitrided Cr-Mo-V steel were not improved in the solution of 1 N HCl and NaOH. Therefore, it is necessary that the continuous study for improvement of corrosion resistance hereafter.