Partially-stabilized ZrO2 Research Articles

Current-driven spontaneous infiltration of molten Al into a porous PSZ preform with a lamellar structure

In this work we proposed a novel strategy for spontaneous infiltration of molten Al into a porous lamellar Y2O3 partially stabilized ZrO2 (PSZ) architecture prepared by using an ice-templating method. The kinetics of liquid spreading and infiltration under the application of a 10 mA current was investigated. The electrochemically-induced improvement in wettability greatly facilitated the spontaneous infiltration.

Thermal shock behavior of toughened gadolinium zirconate/YSZ double-ceramic-layered thermal barrier coating

Double-ceramic-layered (DCL) thermal barrier coating system comprising of toughened Gadolinium zirconate (Gd2Zr2O7, GZ) as the top ceramic layer and 4.5mol% Y2O3 partially-stabilized ZrO2 (4.5YSZ) as the bottom ceramic layer was fabricated by plasma spraying and thermal shock behavior of the DCL coating was investigated. The GZ top ceramic layer was toughened by addition of nanostructured 3mol% Y2O3 partially-stabilized ZrO2 (3YSZ) to improve fracture toughness of the matrix. The thermal shock resistance of the DCL coating was enhanced significantly compared to that of single-ceramic-layered (SCL) GZ-3YSZ composite coating, which is believed to be primarily attributed to the two factors: (i) the increase in fracture toughness of the top ceramic layer by incorporating nanostructured YSZ particles and (ii) the improvement in strain tolerance through the utilization of 4.5YSZ as the bottom ceramic layer. In addition, the failure mechanisms are mainly attributed to the still low fracture toughness of the top ceramic layer and oxidation of the bond-coat.

Phase transformation behavior of 3 mol% yttria partially-stabilized ZrO2 (3Y–PSZ) precursor powder by an isothermal method

The phase transformation behavior of freeze-dried 3mol% yttria–partially-stabilized zirconia (3Y–PSZ) precursor powder has been studied. When the freeze-dried 3Y–PSZ precursor powder was calcined at 773–1073K for 2h, the crystalline structure was composed of tetragonal and monoclinic ZrO2 as primary and secondary phases, respectively. The freeze-dried 3Y–PSZ precursor powder after calcination at 773K, the monoclinic ZrO2 content abruptly increased from 8.00% to 31.51% and the tetragonal ZrO2 content suddenly decreased from 92.00% to 68.49%, with the duration increasing from 0.5 to 1min. The activation energy of the isothermal transformation from tetragonal to monoclinic was 7.02kJ/mol. The kinetics equation for the phase transformation from tetragonal to monoclinic in the freeze-dried 3Y–PSZ precursor powder between 773K and 1273K for various durations is described as ln(1/1−α)=1/2.61[t2.61(1.50×10−3)2.61exp(−7.02×103/RT)]; whereas, the HRTEM image shows a typical monoclinic ZrO2 domain because of the stress-induced tetragonal to monoclinic ZrO2 martensitic transformation that has occurred.

PSZ, Al2O3, TiO2를 반응소결하여 제조한 쾌삭(快削) 세라믹스

Machinability is important in engineering applications, especially in the current micro-electronics industry. Most ceramic components have complex shapes and hence require machining generally with diamond tools, which incurs a high production cost. Recently, h-BN-containing machinable ceramics have been developed, but these materials are very expensive due to the high raw materials and production costs. Therefore, the development of low-cost machinable ceramics is necessary. In this study, inexpensive Al₂TiO 5 was studied as a replacement for h-BN. Al₂O₃, TiO₂ and partially stabilized ZrO₂(PSZ) powders were mixed with various mole ratios and were sintered at 1500℃ for 1 h. The density, hardness and strength were then measured. The phase analysis and microstructures were observed by XRD and SEM, respectively. The machinability of each specimen was tested by micro-hole machining. The results of this research showed that the produced composites could be used as low-cost machinable ceramics.

ＨＩＰを用いて作製したＺｒＯ２‐基セラミックスの微細構造，機械的性質，イオン伝導

Special attention has been given to ZrO2-based ceramics, such as partially stabilized ZrO2 (PSZ), tetragonal ZrO2 polycrystal (TZP), and ZrO2-toughened Al2O3 (ZTA), to improve the mechanical properties of ceramic materials. Hot isostatic pressing (HIP) is applied to fabricate dense ZrO2-based ceramics from solid solution powders developed by sol-gel techniques. This paper reviews recent research trends and progresses related to the solid solution and composite ceramics focussing on the microstructures, strength and fracture toughness, and ionic conductivity.

ＺｒＯ２−Ａｌ２Ｏ３系におけるＺｒＯ２固溶体粉体の合成とＨＩＰ焼きつ

Special attention has been given to partially stabilized ZrO2 (PSZ), tetragonal ZrO2 polycrystal (TZP), and ZrO2-toughened Al2O3 (ZTA) to improve the fracture toughness (KIC) and bending strength (σb) of ceramics. In a recent study, it was shown that in the system ZrO2-Al2O3, ZrO2 solid solutions (ss) are formed metastably up to ≈40 mol% Al2O3 from amorphous materials prepared by the alkoxy-method. Isostatically hot-pressed ZrO2(ss) ceramics exhibit very high KIC (23 MPa⋅m1/2) and plastic deformation at room temperature, although their σb is weak (≤700 MPa). The texture consists of a homogeneous microstructure with a grain size of ≈50nm. To improve ab, two kinds of ceramics have been fabricated by the addition of a small amount of Y2O3: (1) perfect ZrO2(ss) ceramics and (2) composite ceramics of ZrO2(ss) and a-Al2O3. Composites with a homogeneous dispersed cc-Al2O3 result in a remarkable increase of σb (1445 MPa). The ratio of ZrO2(ss) and α-Al2O3 can be controlled by the amount of Y2O3 addition and sintering temperature. A new method for preparing solid solutions from chlorides using hydrazine monohydrate has been developed in some systems. This paper describes the mechanical properties of PSZ, TZP and ZTA ceramics fabricated using ZrO2(ss) powders prepared by some sol-gel techniques.

ZrO2 and Cu functionally gradient materials prepared by a dynamic ion mixing process

Abstract ZrO2-Cu films have been prepared as functionally gradient materials (FGM) which change continuously from Cu to ZrO2. Partially stabilized ZrO2 (PSZ) and the PSZ-Cu FGM films were prepared on a Cu substrate by a dynamic ion mixing process. Oxygen ion irradiation was essential for the FGM formation of the PSZ-Cu films, because films deposited without oxygen ion irradiation were easily peeled from the substrate during the deposition steps. The electron beam deposition rates of Cu and ZrO2 were individually controlled. The FGM structures were analysed by X-ray photoelectron spectroscopy and transmission electron microscopy. Cu and PSZ crystal grains were finely mixed in the FGM layers. The thermal resistance of the FGMs was examined by a heat test in which the film surface was heated by an Ar + H2 plasma jet. No cracks were observed on the PSZ-Cu FGM surfaces after the test. However, for PSZ film (without the FGM layer) on the Cu substrate, cracks were seen.

The spalling modes and degradation mechanism of ZrO2-8 wt.% Y2O3/CVD-Al2O3/Ni-22Cr-10Al-1Y thermal-barrier coatings

State-of-the-art conventional thermal-barrier coatings consist of a thermalinsulating, partially-stabilized ZrO2 top coat and a bond coat. In this study, a continuous alumina-diffusion-barrier layer was deposited and interposed between the top coat and bond coat by chemical-vapor deposition (CVD). Both the conventional and the experimental TBC systems were cyclically tested at 1000°C, 1050°C, 1100°C, and 1150°C to evaluate and compare oxidation, performance, and fracture behavior. Introduction of the intermediate CVD-Al2O3 layer effectively suppressed the oxidation rate of the bond coat and sufficiently altered its oxidation behavior. The thermal-cyclic life of TBCs was improved by the new system. The failure of the ZrO2-8 wt.% Y2O3/CVD-Al2O3/Ni-22Cr-10Al-1Y TBC specimens was observed to propagate mainly along the lamellar splats of the top coat, and secondarily along the top coat/CVD-Al2O3 interface.

X‐ray Determination of Transformation Zone Size in Toughened Zirconia Ceramics

A revised method to determine the transformation zone size in ceramics containing tetragonal ZrO2 using X‐ray diffraction technique was described. The zone sizes of tetragonal ZrO2 polycrystals (TZP) and partially stabilized ZrO2 (PSZ) containing 2.0 to 5.0 mol% Y2O3 were found to be larger than those determined by the method previously reported. The maximum zone size of TZP containing 2.0 mol% Y2O3 was estimated to be 6.6 μm, whereas it had been determined to be 2.9 μm by the method previously reported.

Microstructural examination of tetragonal - YTTRIA stabilized zirconia

Solid solutions of ZrO2 with small amounts of Y2O3 can stabilize the tetragonal and cubic phases which are formed at high temperature. Fullystabilized cubic ZrO2, owing to its high oxygen-ion mobility, is commonly used as solid-state electrolytes in oxygen monitors. Partially-stabilized ZrO2, containing metastable tetragonal particles in a cubic matrix, has good mechanical and thermomechanical properties. Tetragonal-Yttria-Stabilized Zirconia containing 2-3 mol% Y2O3 with sub-micron grain structures exhibits even higher strengths of the order of 1 GPa and good ionic conductivity. The tetragonal phase stability at low to moderate temperatures (<400°C) as well as mechanical and electrical properties are closely related to the microstructure, particularly grain size and distribution and the nature of the intergranular phase. In this study, heat-treatment effects on microstructure and phase stability in 2 mol% YSZ were investigated.

In situ observation of the martensitic transformation in (Mg,Y)-PSZ

Partially-stabilized ZrO2 (PSZ) ceramics have considerable potential for advanced structural applications because of their high strength and toughness. These properties derive from small tetragonal ZrO2 (t-ZrO2) precipitates in a cubic (c) ZrO2 matrix, which transform martensitically to monoclinic (m) symmetry under applied stresses. The kinetics of the martensitic transformation is believed to be nucleation controlled and the nucleation is always stress induced. In situ observation of the martensitic transformation using transmission electron microscopy provides considerable information about the nucleation and growth aspects of the transformation.

ChemInform Abstract: PRECIPITATION IN PARTIALLY STABILIZED ZIRCONIA

AbstractTransmissionselektronenmikroskopisch wird die Substruktur von partiell stabilisiertem ZrO2 (PSZ) untersucht.

Precipitation in Partially Stabilized Zirconia

Transmission electron microscopy was used to study the sub‐structure of partially stabilized ZrO2 (PSZ) samples, i.e. 2‐phase “alloys” containing both cubic and monoclinic modifications of zirconia, after various heat treatments. Monoclinic ZrO2 exists as (1) isolated grains within the polycrystalline aggregate (a grain‐boundary phase) and (2) small plate‐like particles within cubic grains. These intragranular precipitates are believed to contribute to the useful properties of PSZ via a form of precipitation hardening. These precipitates initially form as tetragonal ZrO2, with a habit plane parallel to the {100} matrix planes. The orientation relations between the tetragonal precipitates and the cubic matrix are image and image