• 한국안전학회지
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• 제23권4호
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• pp.25-29
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• 2008

Recently, new functionally graded material(FGM) that has a spatial variation in composition and properties is developed because of its good quality. This material yields the demands for resistance to corrosion and high temperature in turbine blade, wear resistance as in gears and high strength machine parts. Especially coating treatment in FGM surface brings forth a mechanical weak at the interface due to discontinuous stress resulting from a steep material change. It often, leads cracks or spallation in a coating area around an interface. The behavior of propagation cracks in FGMs was here investigated. The interface stresses were reduced because of graded material properties. Also graded material parameter with exponential equation was founded to influence the stress intensity factor. And the resistance curve with FGM coating was slightly increased.

• 한국표면공학회지
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• 제30권5호
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• pp.347-354
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• 1997

Composite plating is a method of co-depositing fine particles of metallic, non-metallic compound or polymers in the plated layer to improve material properties such as were-resistance, lubrication, or corrosion resistance. Graded Ni-Sic composite coating were produced in this research. Prior to produce Graded Ni-SiC composite coatings, effects of particle size, particle content, pH of electrolyte, temperature, current density, stirring rate on the amount of SiC deposited in the Ni layer were investigated. By manipulating current density and plating time properties of these coating were evaluated by micro-indentation hardness test.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2003년도 추계학술발표회초록집
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• pp.59-59
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• 2003

In recent, various functional coatings on artificial tooth implants have been conducted to enhance the bonding strength between implants and bones. Despite of these efforts, some previous reports argued that an adhesion strength between titanium implant and the final coatings like hydroxyapatite(HA) is weaker than the strength between coating and bone. In order to increase the adhesion force between the final coating and implant surface, TiN/DLC based functionally graded coating, which has higher mechanical strength than the titanium implant, was applied as a middle layer between titanium implant and final coating. Particularly we finally coated a biocompatible hydroxyapatite film on the DLC layer and examined the mechanical properties. As a result, TiN/DLC based functionally graded coating showed the higher adhesion strength compared with hydroxyapatite single layer coating on the titanium implant.

• Corrosion Science and Technology
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• 제2권3호
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• pp.155-160
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• 2003

Plasma spraying technique was used to fabricate functionally graded coating (FGC) of NiCrAIY/YSZ 8wt%$Y_2O_3-ZrO_2$ on a Co-base superalloy (HAYNES 188) substrate. Six layers were coated on the substrate for building up compositionally graded architecture. Conventional thermal barrier coating (TBC) of NiCrAIY/SZ with sharp interface was also fabricated. As-coated FGC and TBC samples were exposed at the temperature of $1100^{\circ}C$ for 10, 50, 100 hours in air. Microstructural change of thermally exposed samples was examined. Pores and microcracks were formed in YSZ layer due to evolution of thermal internal stress at high temperature. The amount of pores and microcracks in YSZ layer were increased with increasing exposure time at high temperature. High temperature oxidation of coatings occurred mainly at the NiCrAIY/YSZ interface. In comparison with the case of TBC. the increased area of the NiCrAIY/YSZ interface in FGC is likely to attribute to forming the higher amount of oxides.

• 한국표면공학회지
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• 제31권2호
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• pp.91-100
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• 1998

NiCrAlY/YSZ(8wt%$Y_2O_3-ZrO_2$) functionally graded thermal barrier coating (FGC) layers on a Co-base superalloy (HAYNESS 188) substrate were fabstrate were fabicated using Ar shielded single torch air plasma spraying method. Functional grading with the stepwise compositional change throughout layer thickness. Microstructural observation trvealed a successful fabrication of NiCrAlY/YSZ FGC. From the results of the curvature measurement, adhesive strength measurement and thermal shock test for the FGC, it was concluded that the optimum conditions of functionally graded coating layer thinkness and compositional pattern exit to enhance the properties of FGC, which is closely related to the internal residual stess distribution witin it.

• 한국산학기술학회논문지
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• 제13권9호
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• pp.4139-4145
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• 2012

본 논문에서는 향후 태양전지 반사방지막에 적용여부를 알기 위하여 굴절률 분포에 따른 반사방지막의 성능을 분석하였다. 기존논문에서 제시되었던 1차, 3차 및 5차 함수의 굴절률 분포를 6층 구조의 두께 180 nm 반사방지막에 적용하고 각 굴절률 분포에 대한 반사율을 계산하고 비교하였다. 또한 새로운 구배형 굴절률(graded index) 구조를 제안하였고, 제안한 구조와 기존의 1차, 3차 및 5차 함수의 반사율과 비교하였다. 그 결과로써, 굴절률 분포가 고차 함수로 갈수록 반사율이 대체적으로 감소하였고, 구배형 굴절률 분포의 경우는 짧은 파장대(500 nm ~ 700 nm 이하)에서는 1차, 3차 및 5차 함수보다 더 높은 반사율을 보였고, 긴 파장대(700 nm 이상 ~ 800 nm)에서는 더 낮은 반사율을 보였다. 따라서 긴 파장대에서는 구배형 굴절률 분포가 기존의 1차, 3차, 5차 함수인 경우보다 더 좋은 반사방지막이 될 수 있다는 것을 발견했고, 이 결과는 긴 적색 가시광선에서 적외선 영역에 적용되는 광소자 및 광필터에 적용 가능하리라 판단된다.

• Journal of Welding and Joining
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• 제20권2호
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• pp.109-115
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• 2002

In the case of using high temperature by coating ceramic/metal, large stress was produced due to difference of thermal expansion coefficient between those. And then lead to delamination. In order to relaxation of the stress A1$_2$O$_3$/SS316 composite powders with $10wt.%Al_2O_3$ compositional gradient and $10wt.%Al_2O_3$ agglomerated powder were made by spray drying method. These powders were sintered to improve the strength and to be plasma sprayed in order to fabricate the FGC(functionally graded coating). The influence of gun power, working distance and Ar pressure on the microstructure of the coating layer was studied in order to optimize the plasma spray conditions. It was proven that the optimum conditions were 40kw gun power, 5cm working distance and $100ft^3/h$ Ar flow for both powders. FGC with 10 compositional steps was fabricated and the total thickness was 1.3mm. FGC was heat treated at $1100^{\circ}C$for 10hours to evaluate the heat resisting characteristics.

• Structural Engineering and Mechanics
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• 제66권3호
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• pp.329-341
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• 2018

This paper considers the smooth receding contact problem between a homogeneous half-plane and a composite laminate composed of an inhomogeneously coated elastic layer. The inhomogeneity of the elastic modulus of the coating is approximated by an exponential function along the thickness dimension. The three-component structure is pressed together by either a concentrated force or uniform pressures applied at the top surface of the composite laminate. Both semianalytical and finite element analysis are performed to solve for the extent of contact and the contact pressure. In the semianalytical formulation, Fourier integral transformation of governing equations and boundary conditions leads to a singular integral equation of Cauchy-type, which can be numerically integrated by Gauss-Chebyshev quadrature to a desired degree of accuracy. In the finite element modeling, the functionally graded coating is divided into homogeneous sublayers and the shear modulus of each sublayer is assigned at its lower boundary following the predefined exponential variation. In postprocessing, the stresses of any node belonging to sublayer interfaces are averaged over its surrounding elements. The results obtained from the semianalytical analysis are successfully validated against literature results and those of the finite element modeling. Extensive parametric studies suggest the practicability of optimizing the receding contact peak stress and the extent of contact in multilayered structures by the introduction of functionally graded coatings.

• Structural Engineering and Mechanics
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• 제64권1호
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• pp.71-79
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• 2017

In this study, interaction of several interface cracks located between a functionally graded material (FGM) layer and an elastic layer under anti-plane deformation based on the distributed dislocation technique (DDT) is analyzed. The variation of the shear modulus of the functionally graded coating is modeled by an exponential and linear function along the thickness of the layer. The complex Fourier transform is applied to governing equation to derive a system of singular integral equations with Cauchy type kernel. These equations are solved by a numerical method to obtain the stress intensity factors (SIFs) at the crack tips. The effects of non-homogeneity parameters for exponentially and linearly form of shear modulus, the thickness of the layers and the length of crack on the SIFs for several interface cracks are investigated. The results reveal that the magnitude of SIFs decrease with increasing of FG parameter and thickness of FGM layer. The values of SIFs for FGM layer with exponential form is less than the linear form.

• 한국산학기술학회논문지
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• 제18권5호
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• pp.565-570
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• 2017

우수한 반사방지막을 얻기 위하여 코팅 층의 구조를 나노입자구조로 만들어 코팅 층에 입사하는 빛을 분산시키거나, 코팅 층의 매질을 다양하게 선택하여 굴절률을 제어하여 반사율을 낮추는 기술이 제안되고 있다. 본 논문에서는 코팅 층의 굴절률 분포를 변화시켜 우수한 반사방지막을 얻는 방법 중 기존논문에서 제시되었던 5차 함수의 굴절률 분포와 제안하는 구배형 굴절률 분포의 반사방지막 특성을 비교하였다. 분석에 사용된 반사방지막 구조는 각각 3, 6, 9층 구조로서 총 두께 180 nm 이고, 입사파의 파장 범위는 300 nm ~ 1100 nm 이다. 각 각 서로 다른 층수에서 반사율을 비교하기 위하여 단층인 경우의 전달매트릭스를 구하고 3, 6, 9층의 구조에서의 반사율을 구하였다. 그 결과 3층의 구조 일 때 제안하는 구배형 굴절률 분포가 약 600 nm ~ 1100 nm 파장 범위에서 5차 함수의 굴절률 분포보다 더 낮은 반사율을 보였다. 향후 이 결과는 가시광선(적색)과 근적외선 영역에 사용되는 광소자 및 광 필터에 응용 가능하리라 판단된다.