• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2014년도 추계학술대회 논문집
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• pp.187-187
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• 2014

In this study, we investigated mechanical properties and surface characteristics of Ti-25Ta-xHf alloys. The samples were manufactured for composition of Ti-25Ta-xHf(x=0 to 15 wt. %) alloys. Each alloy was melted twenty times in an arc-melting vacuum furnace. The microstructural phases and phase transformation of Ti-25Ta-xHf alloys were identified with the aid of an XRF, XRD and DSC. And mechanical properties were investigated using Vickers hardness, nanoindentation, and tensile test.

• 한국표면공학회지
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• 제35권2호
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• pp.122-128
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• 2002

This study was conducted to synthesize the diamond like carbon films by plasma enhanced chemical vapor deposition (PECVD). The effects of gas composition on growth and mechanical properties of the films were investigated. A little amount of hydrogen or oxygen were added to base gas mixture of methane and argon. Methane dissociation and diamond like carbon nucleation were enhanced by installing negatively bias grid near substrate. The deposited films were indentified as hard diamond like carbon films by micro-Raman spectroscopy. The surface and fractured cross section of the films which were observed by scanning electron microscopy showed that film growth is very slow as about 0.3$\mu\textrm{m}$/hour, and relatively uniform with hydrogen addition. Vickers hardness of tungsten carbide (WC) cutting tool increased from about 1000 to 1600~1800 by deposition of DLC film, that of commercial TiN coated tool was about 1270. In cutting test of aluminum 6061 alloy, DLC coated cutting tool showed 1/3 or lower crater and flank wear than TiN coated or non-coated WC cutting tools.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 C
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• pp.1469-1471
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• 2003

The effect of heat treatment on torsion characteristics of high nitrogen steel wire has been studied by using torsion test, micro vickers hardness and scanning electron microscopy. After heat treatment at $600{\sim}700^{\circ}C$, torsion cycle was increased with increasing temperature. Especially, in case of high nitrogen steel wire heat treated at $650^{\circ}C$, torsion cycle was sharply increased. It is estimated that the cold-worked high nitrogen steel wire started to recrystallize around at $640^{\circ}C$ in air atmosphere.

• 한국산업융합학회 논문집
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• 제22권6호
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• pp.649-655
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• 2019

Fracture behaviors of SCM435 high strength bolt have been studied including macroscopic and microscopic fracture observation, Energy Dispersive X-ray Spectroscopy, Vickers hardness test and applied stress evaluation. cracks (ratchet marks) were generated by the repetitive loads acting on the bolts, initial stress of bolt and the stress concentration. The applied stress was found to be slightly higher than the fatigue limit of the material. The initial stress of bolt must be removed, and the mold temperature during the process must be maintained by room temperature. Bolts are recommended to be peened to improve fatigue limit.

• 한국표면공학회지
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• 제54권6호
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• pp.307-314
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• 2021

Diamond-like carbon (DLC) is difficult to achieve sufficient adhesion because of weak bonding between DLC film and the substrate. The purpose of this study is to improve the adhesion between substrate and DLC film. DLC film was deposited on AISI H13 using linear ion source. To improve adhesion, the substrate was treated by dual post plasma nitriding. In order to define the mechanism of the improvement in adhesive strength, the gradient layer between substrate and DLC film was analyzed by Glow Discharge Spectrometer (GDS) and Scanning Electron Microscope (SEM). The microstructure of the DLC film was analyzed using a micro Raman spectrometer. Mechanical properties were measured by nano-indentation, micro vickers hardness tester and tribology tester. The characteristic of adhesion was observed by scratch test. The adhesion of the DLC film was enhanced by active screen plasma nitriding layer.

• 대한금속재료학회지
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• 제49권6호
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• pp.448-453
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• 2011

Pre-aging heat treatment after solution heat treatment (SHT) of Al-0.4 wt%Mg-1.2 wt%Si-0.1 wt%Mn alloy sheets for auto-bodies was carried out to investigate the effect of pre-aging and its conditions on the bake-hardening response. Mechanical properties were evaluated by a tensile and Vickers hardness test. Microstructural observation was also performed using a transmission electron microscope (TEM). It was revealed that pre-aging treatments play a great role in the bake-hardening response. In addition, it was found that the sphere-shaped nanosized clusters that can directly transit to the needle-shaped ${\beta}$" phase during the paint-bake process, not being dissolved into the matrix, are formed at 343 K. The result, reveals that the dominant factor of the bake-hardening response is the pre-aging temperature rather than the pre-aging time.

• 대한소아치과학회지
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• 제36권1호
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• pp.38-45
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• 2009

본 연구는 상품화된 10% CPP-ACP 크림 (Tooth mousse, GC Co., Japan)이 0.05 % NaF 불소 용액 매일 양치법을 대체할 수 있는지 알아보기 위하여, 인공 탈회 병소를 가진 우치 법랑질에 대해 10일간 위 두 가지 방법 단독 혹은 복합 사용의 재광화 효과를 비교하였다. 0.1% thymol 용액에 냉장 보관한 소의 치아를 교정용 레진 (Orthodotic resin, Dentsply international Inc., USA)에매몰한 후 탈회 용액에 96시간 보관하였고, 총 60개의 시편을 5개의 군으로 나누었다; 비처치군 (1군), 0.05% NaF 용액 1분 (2군), Tooth mousse 3분 (3군), 0.05% NaF 용액 1분 처리 후 Tooth mousse 3분 (4군), Tooth mousse 3분 처리 후 0.05% NaF 용액 1분(5군). 재광화 정도는 10일간의 시편 처리 전 후의 Vickers hardness number를 측정하여 비교하였으며, 연구 결과는 다음과 같다. 1. 각 군에서 시편 처리 전후의 표면경도를 paired t-test를 이용하여 비교분석한 결과, 3, 4, 5 군에서만 유의할만한 표면 경도 증가가 나타났다(P < 0.05). 2. 각 군별로 평균 표면 경도 증가량은 5 > 4 > 3 > 2 > 1 군 순이었고, 각 군의 표면경도 증가량을 one-way ANOVA test로 비교분석한 후 Duncan test로 사후 검정한 결과, 4, 5 군은 1, 2, 3 군과 유의할만한 표면경도 증가를 보였으며 (P < 0.05), 다른 군들 간에는 유의할만한 차이를 보이지 않았다. 3. Tooth mousse를 우치에 10일간 적용시킨 결과 0.05% NaF 용액보다 더 많은 표면경도 변화량을 나타냈지만, 통계학적으로 유의할만한 차이는 없었다. 이상의 결과에서 Tooth mousse 사용은 불소 양치가 용이하지 않은 환자들에게 양호한 대체 방안이 될 것으로 사료되며, 또한 불소 적용시 Tooth mousse를 복합 사용하는 것이 추천될 수 있으리라 사료된다.

• 한국주조공학회지
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• 제32권5호
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• pp.231-240
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• 2012

In present study, the effect of heat treatment on the microstructure and mechanical properties of the gravity cast superchargers housing using A356 alloy were investigated. In order to identify the characteristics of superchagers housing casting with heat treatment, Vickers hardness test, electrical conductivity test, opical and scanning electron microscopy were performed. And also, to investigate their mechanical properties, the T6 treated superchagers housing casting in optimum heat treatment condition were carried out tensile test using UTM (Universal Testing Machine).

• 한국표면공학회지
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• 제51권3호
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• pp.139-148
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• 2018

In this study, surface analysis of Ni-Cr and Co-Cr alloys with addition of Ti and Mo for dental CAD/CAM use has been researched experimentally. The surface characteristics of the alloys were examined by Vickers hardness test, bonding strength test, surface roughness test, field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction spectroscopy. The shrinkage of the sintered Ni-Cr alloy alloy was slightly larger than that of Ni-Cr-Ti alloy, and larger than Co-Cr alloy. Also, the addition of Mo showed a tendency to decrease shrinkage somewhat. From the result of XRD analysis, NiCr, $Ni_3Cr$ and $Ni_3Ti$ were observed in the sintered Ni-13Cr-xTi and Ni-13Cr-xMo alloys. In addition, ${\sigma}-CrCo$, $Co_2Mo_3$ and $TiCo_2$ were formed in the sintered Co-Cr-xTi and Co-Cr-xMo alloys. Surface hardness of Ti and Mo added alloy was higher than those of Ni-Cr and Co-Cr alloy. The bond strength between sintered alloy and porcelain was $16.1kgf/mm^2$ for Ni-13Cr alloy, $17.8kgf/mm^2$ for Ni-13Cr-5Ti alloy, and $8.2kgf/mm^2$ for Ni-13Cr-10Ti alloy, respectively.

• 디지털융복합연구
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• 제18권4호
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• pp.341-346
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• 2020

가철성 교정장치에서 주로 사용하고 있는 자가중합 레진인 Polymethyl methacrylate (PMMA)는 현대 치의학 분야에서 주로 쓰이고 있는 아크릴릭 레진이다. 장점으로 색과 체적의 조직 친화성, 안정성 등 있어 치과에선 교정장치 재료로 오랫동안 사용해 왔다. PMMA의 제작은 활성화 방법에 따라 자가중합방식과 열중합 방식으로 나눌 수 있다. 자가중합 레진은 치과 교정장치로 오래동안 사용되고 있다. 레진의 주입방법은 크게 적층법(sprinkle-on method)와 혼합법(mixing method)이 있다. 본 연구에서는 교정장치의 레진 주입방법에 따른 기계적 특성인 강도, 탄성계수 경도, 표면조도를 실험 해보고자 한다. Orthodontic PMMA 의 직사각형 시편 (1.4×3.0×19.0 mm)에 3점 굽힘강도 실험한 결과 강도에선 유의한 차이가 없었다. 경도 역시 유의한 차이가 없었다. 표면조도도 큰 차이가 보이지 않았다. Orthodontic PMMA는 교정용 장치의 레진주입 방식에 따른 기계적 특성의 유의한 차이가 없음을 확인하였다.