• 한국재료학회지
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• 제24권12호
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• pp.652-657
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• 2014

The purpose of this study was to investigate the microstructures and mechanical properties of zirconia toughened alumina (ZTA) ceramics prepared from two kinds of 3Y-TZP powders. ZTA composites were prepared by adding two kinds of 3Y-TZP powders, 3YEH (BET = $7m^2/g$) and 3YEM (BET = $16m^2/g$), to ${\alpha}$-alumina in the range of 5-25 wt%. It was found that the microstructure photographs of the ZTA composites showed that the average grain size of alumina decreased as the content of zirconia increased. In our present study, specimens containing 3YEM zirconia exhibited smaller grain sizes compared to those of 3YEH zirconia. The Vickers hardness of the ZTA composites that were sintered at $1600^{\circ}C$ for 2 hrs was found to smoothly decrease with increasing zirconia content because of the low Young modulus in zirconia. The Vickers hardness of the ZTA containing 3YEH zirconia was greater than that of the 3YEM zirconia. In substance, the fracture toughness ($K_{1c}$) of the ZTA composites increased as the content of zirconia increased. The fracture toughness ($K_{1c}$) of ZTA containing 3YEM zirconia was greater than that of 3YEH zirconia.

• 스마트미디어저널
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• 제12권2호
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• pp.15-26
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• 2023

전 세계적인 COVID-19 팬데믹으로 인해 업무처리 방식이 원격으로 전환됨에 따라 기업의 외부에서 내부 중요리소스에 접근하는 빈도가 기하급수적으로 증가하였고 기업은 각종 보안 위협에 쉽게 노출되었다. 이러한 접근 보안 문제를 해결하기 위해 ZTA(Zero Trust Architecture) 솔루션이 주목받고 있다. ZTA는 사전에 설정한 정책에 따라 접근에 대한 인증과 허가를 엄격하게 관리하며 외부 유저는 물론 내부 유저도 신뢰하지 않는다는 원칙을 기반으로 동작한다. 본 논문에서는 ZTA의 정의를 포함해 주요 연구 동향을 분석하였고 각 기업별로 상이한 ZTA 솔루션을 정리하였다.

• 한국세라믹학회지
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• 제31권1호
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• pp.17-24
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• 1994

Al2O3-ZrO2(ZTA) composites were fabricated by a surface-induced coating of the precursor for the ZrO2 phase on the kinetically stable colloid particles of Al2O3. The fabricated composites were characterized by a uniform spatial distribution of the dispersed ZrO2 phase and by the absence of large ZrO2 grains throughout the Al2O3 matrix. The fracture toughness (KIC) and the bending strength of ZTA composites sintered at 1$600^{\circ}C$, respectively, were 5.6 MPa.m1/2 (for 20 wt% ZrO2) and 600 MPa (for 15wt% ZrO2). The fraction of tetragonal ZrO2 phase decreases as the total content of ZrO2, suggesting that both the stress-induced tlongrightarrowm transformation and the microcrack nucleation contribute to the toughening of the ZTA composites fabricated by the surface-induced coating.

• 한국재료학회지
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• 제23권4호
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• pp.250-254
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• 2013

In order to increase the toughness of ZTA(zirconia toughened alumina) ceramics, the present study focused on rearrangement and densification of particles according to the particle size of the parent material. When rough alumina was used for production of ZTA, densification behavior was observed in the specimen sintered at a temperature over $1550^{\circ}C$. However, it was found that the densification behavior was occurred in the specimen sintered at $1450^{\circ}C$ when fine alumina powder was used. High relative density exceeding 98% was obtained when fine alumina powder was mixed with 15 wt% of 3Y-TZP and sintered at $1600^{\circ}C$. Also, a hardness of 1820.2 Hv was obtained when a specimen containing 10 wt% of 3Y-TZP was sintered at $1600^{\circ}C$. In the case of 3Y-TZP containing rough alumina powder that had been sintered the hardness value was around 1720.3 Hv. It was predicted that an improved toughening effect in ZTA could be achieved by using finer alumina powder as the parent material.

• 한국재료학회지
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• 제16권12호
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• pp.743-746
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• 2006

ZTA tubes were prepared by centrifugal casting and sintered at $1600^{\circ}C$ for 2 hrs. The ZTA tubes were machined into specimens of $3{\times}4{\times}40$ mm. Molten Soda lime glass (SLG) was penetrated into the surface of ZTA at an optimized condition of $1500^{\circ}C$ for the holding time of 5 h and furnace cooled. The extra glass on the surface was removed using a resin bonded diamond wheel. The glass penetrated samples were tested for their flexural strength using four point bend test. Vickers Indentation cracks were made on the glass penetrated surface at different loads of 9.8 N, 49 N, 98 N and 196 N. The residual compression on the surface enhanced the flexural strength and crack arrest behaviour remarkably. This was attributed to the thermoelastic mismatch between the glass and ZTA matrix during cooling.

• 한국세라믹학회지
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• 제27권3호
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• pp.369-382
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• 1990

ZrO2-Toughened Alumina-Ceramics(ZTA) with Cr2O3 and HfO2 as addition were synthesized by assintering method for solid solution of Al2O3/Cr2O3 and ZrO2/HfO2, and were prepared by pressureless sintering at 1$600^{\circ}C$. The effects of Cr2O3 and HfO2 on the thermal and mechanical properties, the sintering mechanism, and the wearness between theory and experiment were investigated. Among three kinds of mechanisms such as stress-induced transformation, microcracking, and crack deflection it contributed to the ZTA system with a few exceptons according to composite. We show that wearness can be estimated sufficiently by HV and KIC through theory and experiment.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1997년도 Proceedings of the 12th KACG Technical Meeting and the 4th Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.13-17
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• 1997

The densification of $Al_2$O$_3$/15v/o ZrO$_2$ (Zirconia Toughened Alumina: ZTA) to the 99% of theoretical density was attempted by controlling the processing parameters affecting the each processing step i.e., milling, spray-drying, forming and pressureless sintering. The ZTA processed under the identical conditions showed a large variation in the green and sintered densities, and the mechanical properties. The deviation of 4-point bending strength was more than 100MPa for the ZTA with ~99% of theoretical density. Moreover, the relative green and sintered densities were deviated greatly from the average value. This low reproducibility could be caused by the variation of spray-dried granule properties. Thus, the effect of yield strength and morphology of spray-dried ZTA granule on the green and sintered densities and the mechanical properties needs to be studied in detail. The objective of this work is to fine out the optimum condition of compaction pressure and compaction method depending on the properties of spray-dried granules.

• 한국세라믹학회지
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• 제27권3호
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• pp.329-336
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• 1990

In this investigation, bar-shaped specimens which consisted of three layers are prepared to study the effects of residual compressive stress on the mechanical properties in ZTA. The outer layers contained Al2O3 and unstabilized ZrO2 and the central layer contained Al2O3 and stabilized ZrO2(with 5.10wt% Y2O3). When cooled from the sintering temperature, some of zirconia in the outer layers transformed to the monoclinic form while zirconia in the central layer was retained in the tetragonal form. The transformation which induces to dilatational expansion led to the estabilishmenet of compressive stress in the outer layers and balances tensile stress in the central layer. Decrease of outer layer thickness(for a fixed total thickness)increases residual compressive stress. Because of residual compressive stress in the outer layers, the fracture toughness of outer layers of 3-layers composite is 10.21 Mpam1/2, which is increased to 25% above in comparison with 1-layer specimens in ZTA. Also, the 3-layers composite is believed to exhibite greater fracture resistance in contact damage environment from thermal shock test.

• 한국결정성장학회지
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• 제8권2호
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• pp.356-364
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• 1998

$ZTA:\;Al_2O_3/\;15\;vol{%}\;ZrO_2$ (Zirconia Toughened Alumina : ZTA)를 상압소결에 의해 제조시 분무건조한 granule의 특성에 따른 성형밀도 및 소결밀도의 변화를 고찰하여, 소결밀도의 재현성을 향상시킬 수 있는 성령 공정 조건을 제시하였다. 결합제의 첨가 유무에 따라 granule의 구형도, 평균크기, granule 내의 hollow의 생성정도, 수분함유량 등이 다름을 확인하였다. granule의 물성 차이가 성형거동에 미치는 영향을 성형압(80~120MPa)과 성형방법(일축성형과 정수압 성형)에 따른 성형밀도의 변화를 통하여 조사하였다. granule의 특성 변화에 의한 밀도의 낮은 재현성은 성형압과 성형방법의 최적화를 통하여 극복될 수 있음을 확인하였다. 즉 가능한 낮은 압력(80MPa)에서 일축성형한 후 고압(500MPa)에서 정수압 성형하였을 때 소결후 밀도변화는 1%이내에서 조절되었다.

• 한국세라믹학회지
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• 제28권9호
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• pp.696-704
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• 1991

ZrO2-Toughened Alumina-Ceramics (ZTA) with SiC Whisker as dispersive additive were prepared by pressureless sintering at 1$600^{\circ}C$ and 1$650^{\circ}C$ and by HIPing at 1$600^{\circ}C$ in Ar atmosphere. Effects of SiC-Whisker addition on microstuructural, mechanical, and thermal properties were investigated and the toughening mechanisms between theory and experiment were compared. Specimens with 15 vol% Whisker prepared by HIPing showed 8.26 MPa.ma1/2 in fracture toughness and 600 MPa in flexural strength owing to contribution of the three mechanisms such as crack deflection, whisker bridging and whisker pullout in spite of difference between the theoretical and experimental values due to the partial inhomogeneous dispersion of SiC-Whisker in the matrix and the processing flaw.