Mechanical Behavior of Layered YSZ Thermal Barrier Coatings using Indentation Test

In this study, we investigate the effect of porous Al 2 O 3 substrate on the strengths of asymmetric structures after we prepare such a structure consisting of a dense Li 2 ZrO 3 top layer and porous Al 2 O 3 substrate layer. The porosity and elastic modulus of the substrate layer are controlled by sintering temperature, which has three values of 1150, 1250 and 1350 o C. The porosity is controlled in the range of ~ 30-50 vol%, elastic modulus is ~80-120 GPa and elastic mismatch E s /E c is ~ 0.6-1.0. Indentation stressstrain curves are obtained and analyzed to evaluate the yield stress of the asymmetric structure by concentrated local loading of WC balls. Conventional flexural strengths are also obtained to evaluate the strength of the asymmetric structure. The results indicate that the local yield strength of the asymmetric structure has mid-values between the top and the substrate layer; however, the flexural strength of the asymmetric structure are mainly influenced by elastic modulus and strength of the substrate.

Section: Methodsmentioning

confidence: 99%

Effect of Porous Substrate on the Strength of Asymmetric Structure

Kim¹,

Park²,

Kim³

et al. 2015

“…파손을 방지하기 위한 도자기, 식기에 도입되는 유약뿐만 아니라 자동차 라미네이트(laminate) 유리, 5,6) 절삭공구, 베 어링 등의 기계구조용 부품, 치아, 인공 뼈 등에 적용되 는 바이오 코팅재 7,8) 필터 및 분리막 제품의 비대칭 구조 체, 9,10) 가스터빈 부품을 보호하기 위한 코팅재 [11][12][13] 원형균열은 표면에 수직한 균열이 형성되다가 σ 33 의 방향 으로 원추형 모양의 균열(cone crack)로 진전되어 표면에 서 링 형태의 균열로 관찰되는 것이며, 19) 방사형 균열은 코팅층과 모재층 간 계면으로부터 코팅층에 작용하는 굽…”

Section: -4)unclassified

Mechanical Behavior of Glass/Porous Alumina by Contact Loading

Kim¹,

Kim²,

Kim³

et al. 2014

Porous alumina with different porosities, 5.2-47.5%, were coated with cover-glass having a thickness of 160 µm, using epoxy adhesive. We investigated the effect of the porosity of the substrate layer on the crack initiation load, and the size of cracks propagated in the coating layer. Hertzian indentations were used to evaluate the damage behavior under a constrained loading condition. Typically, two types of cracks, ring cracks and radial cracks, were observed on the surface of the glass/porous alumina structure. Indentation stress-strain curves, crack initiation loads, crack propagation sizes, and flexural strengths were investigated as a function of porosities. The results indicated that a porosity of less than 30% and a higher substrate elastic modulus were beneficial at suppressing cracks occurrence and propagation. We expect lightweight mechanical components with high strength can be successfully fabricated by coating and controlling porosities in the substrate layer.

“…세라믹스 열차폐 코팅재의 코팅 방법으로서는 대기 플 라즈마 용사법(APS, atmospheric plasma spraying) [1][2][3][4] , 전 자 빔 물리적 증착법(EBPVD, electron beam physical vapor deposition) [5][6][7][8] , 감압 플라즈마 용사법(LPPS, low pressure plasma spray), 진공 플라즈마 용사법(VPS, vacuum plasma spray), 용액 전구체 플라즈마 용사법(SPPS, solution precursor plasma spray) [9][10] , 고속 화염 용사법(HVOF, high velocity oxygen fuel) 등 여러 가지 방법이 있으나, 설비 는 인자(factor)로 작용할 수 있음이 여러 문헌에서 보고 되고 있다. [11][12][13] 이러한 코팅용 분말을 제작하기 위한 공 정의 하나로서 분무 건조법(spray drying)에 의한 방법이 용사코팅을 위한 분말로서 폭넓게 활용되고 있다.…”

Section: 서 론unclassified

Fabrication and Characterization of Zirconia Thermal Barrier Coatings by Spray Drying and Atmospheric Plasma Spraying

Kim¹,

Heo²,

Kim³

et al. 2013

In this study, we prepared yttria stabilized zirconia granules for thermal barrier coatings using a spray drying process. First, we characterized the properties of granules such as flow rate and packing density for utilizing the air plasma spray process. The flow rate and packing density data showed 0.732 g/sec and 2.14 g/cm 3 , respectively, when we used larger and denser particles, which are better than hollow granules or smaller spherical granules. Second, we chose larger, spherical granules fabricated in alcohol solvent as starting powders and sprayed it on the bondcoat/nimonic alloy by an atmospheric plasma spray process varying the process parameters, the feeding rate, gun speed and spray distance. Finally, we evaluated representative thermal and mechanical characteristics. The thermal expansion coefficients of the coatings were 11~12.7 × 10 −6 / o C and the indentation stress measured was 2.5 GPa at 0.15 of indentation strain.