• Journal of Welding and Joining
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• v.11 no.4
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• pp.91-102
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• 1993

The plasma sprayed $Cr_3C_2$-NiCr coatings are widely used as wear-resistant and corrosion-resistant materials. The mechanical and wear properties of the plasma sprayed $Cr_3C_2$-NiCr coating on steel plate were examined in this study. The pore in the coatings could be classified into two types, the one is the intrinsic pore originated from the spraying powder, the other is the extrinsic pore formed during spraying. During the tensile adhesion test, the fracture occured at the interface of top coating and bond coating. It is though that the compressive residual stress increases with the increase of the top coating thickness. From the wear test, it was found that the wear rate increased with the increase of the sliding velocity regardless of the temperature. It is thought that the fracture toughness reduces with the increase of the sliding velocity at $30^{\circ}C$ and that the adhesion amount increases with the increase of the sliding velocity at $400^{\circ}C$ It is concluded that the wear mechanism at $30^{\circ}C$ is the fracture and pull-out of the carbide particles due to the fatigue on sliding surface, while the wear mechanism at $400^{\circ}C$ is the adhesion of the smeared layer formed during wear process.

• Journal of Surface Science and Engineering
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• v.34 no.5
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• pp.421-428
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• 2001

New WC-CrN superlattice film was deposited on Si substrate (500$\mu\textrm{m}$) using cathodic arc ion plating system. The microstructure and mechanical properties of the film depend on the superlattice period (λ). In the X-ray diffraction analysis (XRD), preferred orientation of microstructure was changed according to various superlattice periods(λ). During the Transmission Electron Microscope analysis (TEM), microstructure and superlattice period (λ) of the WC - CrN superlattice film was confirmed. Hardness and adhesion of the deposited film was evaluated by nanoindentation test and scratch test, respectively. As a result of nanoindentation test, the hardness of WC - CrN superlattice film was gained about 40GPa at superlattice period (λ) with 7nm. Also residual stress with various superlattice period (λ) was measured on Si wafer (100$\mu\textrm{m}$) by conventional beam-bending technique. The residual stress of the film was reduced to a value of 0.2 GPa by introducing Ti - WC buffer layers periodically with a thickness ratio ($t_{buffer}$/$t_{buffer+superlattice}$ ). To the end, for the evaluation of oxidation resistance at the elevated temperature, CrN single layer and WC - CrN superlattice films with various superlattice periods on SKD61 substrate was measured and compared with the oxidation resistance.

• Journal of Technologic Dentistry
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• v.39 no.1
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• pp.43-52
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• 2017

Purpose: Physical and chemical properties of gold is most suitable to be restored of teeth to its original state. Recently zirconia was used instead of gold because of esthetical and intimacy of human body. Because of high strength and high abrasion resistance of zirconia, all zirconia artificial tooth lead to wear the original tooth of opposite site. To preserve this original tooth, zirconia artificial tooth covered with dental ceramic glass was used. When joining the zirconia core and dental ceramic glass, difference of their thermal expansion coefficient and wetting ability is generated the residual stress at interface lead to crack. In order to solve this problem, intermediate layer what is called zir-liner was imported to decrease the residual stress and increase the bonding strength. Methods: In this study, to identify the optimum conditions for manufacturing process, various methods to rough the surface of zirconia core were adopted, and vary the thickness of interlayer, and analyzed bond strength. Results: Bond strength of sanding specimens group showed higher than that of non-sanding specimens group, and once applied intermediate layer with sanding specimens showed highest bond strength with 28 MPa. SEM photomicrographs of zirconia cores fired at $1500^{\circ}C$ showed parallel straight lines in sanding and pockmarked surface in blasting surfaces as abrasion traces. Observation of the destruction section after shear test by SEM were carried out. Liner applied non-sanding group and non-liner applied sanding group all showed interfacial crack. Sandblasting group with non-liner showed remained dental ceramic glass on the surface of zirconia. Sandblasting group with once applied liner showed partially remained liner and dental ceramic glass on the surface of zirconia. XRD analysis revealed that sandblasting group showed higher monoclinic peaks than other specimens group and this result was due to the high collision energy for stress induced phase transformation. Conclusions: A study on the improvement of bonding strength between zirconia and dental ceramic glass steadily carried out for the future to practical use.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.30-35
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• 1999

For dolomite clinkers used as stamp materials, the corrostion behavior of those by slag was inverstigated between 1550$^{\circ}C$ and 1650$^{\circ}C$. Fe2O3 among slag components was selectively penetrated into the grain boundaries of dolomite clinkers. In hot face, the magnesioferrite was preferentially formed by Fe2O3 component contained in dolomite clinker rather than Fe2O3 of slag. The corrosion steps of dolomite clinkers by slag were found as follows ; (1) The dicalciumferrite was formed by the reaction of the calcia within dolomite clinkers with Fe2O3 of slag. (2) The magnesia within dolomite clinkers reacted with the dicalciumferrite to from magnesioferrite and the residual calcia within dolomite clinkers reacted with the dicalciumferrite to form magnesioferrite and the residual calcia was dissolved into slag. (3) The magnesioferrite was corroded by CaO-SiO2 compounds of slag. With the temperature of slag increased, the magnesioferrite layer in hot face was decreased for dolomite clinker without Fe2O3 while the layer thickness and grain sizes of magnesioferrite was increased for dolomite clinker with Fe2O3.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.146-150
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• 1996

A thermal micro actualtor has been fabricated using surface micromachining techniques. It consists of doped ploysilicon as a moving part and TEOS(Tetra Ethyl Ortho Silicate) as a sacrificial layer. The polysilicon was annealed for the reduction of residual stress which is the main cause to its deformation such as bending and buckling. And the newly developed HF VPE(vapor phase etching)process was also used as an effective release method for the elimination of sacrificaial layer. With noliquid involved during any of the steps for relasing, unlike other reported relase techniques, the HF VPE pocess has produced polysilicon microstructures with virtually no process-induced stiction problem. The actuation is incured by the thermal expasion due to current flow in active polysilicon cantilever, which motion is amplified bylever mechanism. The thickness of pllysilicon is 2 .mu. m and the length of active and passive polysilicon cantilever are 500 .mu. m, respectively. The moving distance of polysilicon actuator was experimentally conformed as large as 21 .mu. m at the input voltage level of 10 V and 50Hz square wave. These micro actuator technology can be utilized for the fabrication of MEMS (microlectromechanical system) such as microrelay, which requires large displacement or contact force but relatively slow response.

• Journal of Surface Science and Engineering
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• v.34 no.1
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• pp.3-9
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• 2001

The purpose of this study is to evaluate the properties of the functional gradient thermal barrier coatings by plasma spray process. The evaluations of mechanical and thermal properties such as fatigue, oxidation and wear-resistance at high temperatures have been conducted. Furthermore, residual stress and bond strength have been evaluated. The range of thickness of coated layers was 550~600$\mu\textrm{m}$. The range of hardness of layers was 800~900 Hv and the porosity range of coatings was about 7 to 14%. The top coating layer of $ZrO_2$ in thermal barrier was composed of tetragonal structure after spraying. The coated layers of $ZrO_2$ on the Inconel substrate is the best resistance for thermal fatigue. Those coatings had the least compressive stress in comparison with other coatings. In high temperature oxidation test, the coatings on Inconel substrate was better than the coatings on SUS substrate. The bond strength of the concave type was greater than that of linear types and convex types coatings.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.126-126
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• 2004

1996년 Chou 등이 개발한 가열방식의 나노임프린트 리소그래피(nanoimprint lithography, NIL)은 선폭 100nm 이하의 나노구조물을 경제적으로 제작할 수 있는 대표적인 나노패턴닝(nano-patterning) 공정으로 많은 기대가 모아지고 있으나, 열변형에 의해 다층정렬이 어렵다는 점과, 점도가 큰 레지스트(resist)를 임프린트하기 위해서는 고압(∼30 bar)이 필요하다 점 등의 문제점이 있다. 이를 해결할 수 있는 방법으로 UV 나노임프린트 리소그래피(ultraviolet nanoimprint lithography, UV-NIL)를 들 수 있다.(중략)

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.137-138
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• 2012

박막태양전지의 경우 기판재와 태양전지를 구성하는 반도체 층간의 열팽창 거동 차이가 태양전지의 변형을 야기한다. 이러한 열변형은 태양전지의 효율에 영향을 주는 것으로 알려져 있다. 그러므로 태양전지를 구성하는 반도체 층과 열팽창 거동이 유사한 기판재의 적용이 필요하다. 본 연구에서는 연성 CIGS 태양전지를 구성하는 기판과 박막층의 두께변화가 열공정 중 발생하는 잔류응력에 미치는 영향을 전산해석 하고자 하였다. 전산해석 결과 Fe-52wt%Ni 기판재의 두께가 증가함에 따라 CIGS 박막층 내부의 잔류응력은 감소하였다. SiO2 절연층의 두께가 증가하면 CIGS 박막층의 잔류응력이 증가하였다. Mo 후면전극층이 얇아지면 잔류응력이 감소하였으나 CIGS층의 두께변화는 CIGS층의 잔류응력에 큰 영향을 미치지 않았다.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.10
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• pp.897-902
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• 2015

This study reports on a uniform resin coating method by using a doctor blade type dispenser. For high productivity, continuous imprint-lithography has been studied, and developed fabrication systems are used in several applications such as anti-reflection films, dry adhesives, and water collecting surfaces. In the continuous fabrication field, researchers have typically focused on patterning and demolding procedures. During the roll-to-roll fabrication process, however, the uniform resin coating process is also important in order to obtain a high quality product, which can be evaluated by uniform thickness, precise geometric expressions, and a thin residual layer. To achieve these, a doctor blade type dispenser was designed and fabricated. As a result, thickness of coated resin was well controlled by modulating the flow rate of the resin and blading gap. In addition, a very thin layer coating process (${\sim}10{\mu}m$) was achieved by softly contacting the blade on the substrate.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.7
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• pp.613-620
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• 2017

A metal-coated FBG (fiber Bragg grating) sensor has a memory effect, which can recall the maximum strains experienced by the structure. In this study, a nickel-coated FBG sensor was fabricated through electroless (i.e., chemical plating) and electroplating. A thickness of approximately $43{\mu}m$ of a nickel layer was achieved. Then, we conducted cyclic loading tests for the fabricated nickel-coated FBG sensors to verify their capability to produce residual strains. The results revealed that the residual strain induced by the nickel coating linearly increased with an increase in the maximum strain experienced by the sensor. Therefore, we verified that a nickel-coated FBG sensor has a memory effect. The fabrication methods and the results of the cycle loading test will provide basic information and guidelines in the design of a nickel-coated FBG sensor when it is applied in the development of structural health monitoring techniques.