• Korean Journal of Metals and Materials
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• v.48 no.6
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• pp.506-513
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• 2010

The composite coatings of $(ZrO_2-8Y_2O_3)$/(Ni-22Cr-10Al-1Y) were prepared by the air plasma spraying method. They consisted of (Ni,Cr)-rich regions,$(ZrO_2-Y_2O_3)$-rich regions, and $Al_2O_3$-rich regions that were formed by oxidation of Al from (Ni-22Cr-10Al-1Y) during spraying. The coatings corroded at 800 and $900^{\circ}C$ in NaCl-$Na_2SO_4$ molten salts up to 50 hr. Ni, Cr and Al oxidized to NiO, $Cr_2O_3$ and ${\alpha}-Al_2O_3$, respectively. These oxides and $(ZrO_2-Y_2O_3)$ were dissolved off into the molten salts during hot corrosion, which resulted in the ever-lasting corrosion of the composite coatings. Chromium diffused out from the (Ni,Cr)-rich regions and oxidized to $Cr_2O_3$, which was most frequently found as surface scales. Aluminum retained in the (Ni,Cr)-rich regions were similarly diffused out.

• Journal of the Korean Ceramic Society
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• v.43 no.9 s.292
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• pp.515-518
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• 2006

The microstructure of $ZrO_2$ toughened $Al_2O_3$ ceramics was carefully controlled so as to obtain dense and fine-grained ceramics, thereby improving the properties and reliability of the ceramics for capillary applications in semiconductor bonding technology. $Al_2O_3-ZrO_2(Y_2O_3)$ composite was produced via Ceramic Injection Molding (CIM) technology, followed by Sinter-HIP process. Room temperature strength, hardness, Young's modulus, thermal expansion coefficient and toughness were determined, as well as surface strengthening induced by the fine grained homogenous microstructure and the thermal treatment. The changes in alumina/zirconia grain size, sintering condition and HIP treatment were found to be correlated.

• Journal of the Korean Ceramic Society
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• v.31 no.5
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• pp.513-519
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• 1994

Alumina composite was fabricated by introducing tetragonal ZrO2 in alumina composite of $\alpha$-alumina reinforced with in-situ formed La-$\beta$-aluminate (LaAl11O18). The powder mixture of composition (100-x)[88 Al2O3+(La2O3+11 Al2O3)]+x vol% ZrO2 was prepared with x from 0 to 40. Dense composites fabricated by hot-pressing exhibited bending strength up to 1200 MPa. The gain growth inhibiting effect of ZrO2 grains and La-$\beta$-aluminate platelets, and possibly the stress-induced phase transformation of ZrO2 have resulted in the high bending strength. The fracture toughness of the composite also increased up to 8.5 MPa.m1/2. The enhancement in toughness can be explained by transformation and microcrack toughening of ZrO2 and by crack deflection and bridging of La-$\beta$-aluminate platelets and ZrO2.

• Journal of the Korean Ceramic Society
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• v.41 no.1
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• pp.1-8
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• 2004

The microstructural features and mechanical behavior of directionally solidified $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fibers after extended beat treatment in oxidizing environment were investigated. The fiber was grown continuously by an Edge-defined Film-fed Growth (EFG) technique. The microstructure was characterized using X-Ray Diffraction (XRD) and Scanning Electron Microscopy(SEM). The microstructure of the fiber in the as-fabricated state consists of highly oriented colonv and fine lamellar microstructure along the fiber axis. Tensile strength of the $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fiber remained unchanged with heat treatment at temperatures between $1200^{\circ}C$ and $1500^{\circ}C$ up to 300h. The weibulls modulus remained fairly constant after extended thermal exposure. The fracture toughness and crack propagation behavior were investigated. The fracture toughness ($K_{1C}$) of the $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fiber in the as-fabricated state were measured to be 3.6 ${\pm}$ 0.5 MPa${\cdot}m^{1/2}$ by an indentation technique and 2.2 ${\pm}$ 0.2 MPa${\cdot}m^{1/2}$ by assuming elliptical flaw of a semi-infinite solid, respectively. The $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fiber showed a radial (Palmqvist) crack type and exhibited an orthotropic crack growth behavior under 100 g load.

• Journal of Power System Engineering
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• v.12 no.3
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• pp.60-65
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• 2008

This study aims at investigating the wear properties of thermally sprayed $Al/Al_2O_3$ metal matrix composite(MMC) coating against different counterparts. $Al/Al_2O_3$ MMC coatings were fabricated using a flame spray system on an Al 6061 substrate. Dry sliding wear tests were performed using the sliding speeds of 0.2m/s and the applied loads of 1 and 2 N. AISI 52100, $Al_2O_3$, $Si_3N_4\;and\;ZrO_2$ balls(diameter: 8mm) were used as counterpart materials. Wear properties of $Al/Al_2O_3$ MMC coatings were analyzed using a scanning electron microscope(SEM) and energy dispersive X-ray spectroscopy (EDX). It was revealed that wear properties of $Al/Al_2O_3$ composite coatings were much influenced by counterpart materials. In the case of AISI 52100 used as counterparts, the wear rate of composites coating layer increased according to the increase of the applied load. On the contrary, in the case of ceramics used as counterparts, the wear rate of composites coating layer decreased according to the increase of the applied load.

• Proceedings of the Materials Research Society of Korea Conference
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• 1998.11a
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• pp.84-84
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• 1998

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.296-297
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• 2014

고체윤활제는 고온부품의 응용에 매우 적합한 소재이다. 세라믹스를 기반으로 하는 고온저마찰소재는 우주항공, 발전시설 등과 같은 다양한 분야에서 매우 중요하다. 본 연구는 고온저마찰 소재를 가지는 자기윤활 $Al_2O_3-ZrO_2$ 세라믹 복합 코팅층의 마찰마모거동에 초점을 맞추고 있다. 이 자기윤활 $Al_2O_3-ZrO_2$ 세라믹 복합 코팅층은 대기플라즈마 용사법으로 제작하였으며, 비윤활상태에서 마찰마모거동을 조사하였다.

• Journal of the Korean Ceramic Society
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• v.36 no.12
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• pp.1381-1389
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• 1999

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1436-1438
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• 2001

The $\beta$-SiC + $ZrB_2$ ceramic electroconductive composites were pressureless-sintered and annealed by adding 12wt% $Al_2O_3$ + $Y_2O_3$ (6 : 4wt%) powder as a function of sintering temperature. The relative density showed the highest value of 81.1% at 1900$^{\circ}C$ sintering temperature. The phase analysis of the composites by XRD revealed of $\alpha$-SiC(6H), $TiB_2$, $Al_5Y_2O_{12}$ and $\beta$-SiC(15R). Flexural strength showed the highest value of 230 MPa for composites sintered at 1900$^{\circ}C$. The vicker's hardness and the fracture toughness showed the highest value of increased with increasing sintering temperature and showed the highest of 9.88 GPa and 6.05 $MPa{\cdot}m^{1/2}$ at 1900$^{\circ}C$. The electrical resistivity was measured by the Pauw method from 25$^{\circ}C$ to 700$^{\circ}C$. The electrical resistivity of the composites showed the PTCR (Positive Temperature Coefficient Resistivity).

• Proceedings of the KAIS Fall Conference
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• 2001.05a
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• pp.40-46
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• 2001

The thermal stability of $Al_2TiO_{5}$ ceramics was improved by formation of solid solution with MgO, such as $MgAl_2O_4$ spinel through electrofusion in an arc furnance, and by limitation of grain size and microcracks with $SiO_2$, $ZrO_2$ and ${\alpha}$-$Al_2O_3$. The low thermal expansion properties of $Al_2TiO_{5}$ composites show the thermal hysteresis curves due to the strong anisotropy of $Al_2TiO_{5}$. These phenomena are explained by the opening and closing of microcracks. The relation between thermal hysteresis, microstructures and sintering temperature were studied by dilatometry.