Papers by Keyword: YSZ

Abstract: The effect of impurity Ce on the mechanical and thermal properties of tetragonal ZrO2 stabilized by rare earth element Y (YSZ) have been studied using first principles density functional theory within generalized gradient approximation (GGA) for the exchange correlation potential. The predicted elastic constants indicate that YSZ and Ce doped YSZ (CeYSZ) are mechanically stable structures. And then the numerical estimates of bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, sound velocity and minimum thermal conductivity were performed using the calculated elastic constants and analyzed for the first time. The values of sound velocity from different orientations are also reported. The agreement between the results of the available experiments and our calculations was satisfactory. Our calculated results indicate that Young’s modulus, hardness, mean sound velocity and minimum thermal conductivity of YSZ can be decreased by Ce substitution. The reasons are from the “softened” Ce-O bond strength using bond population and relative volume change under external hydrostatic pressure. Chemical bonding nature was also analyzed from the density of states and electron density difference.

Abstract: TBC (Thermal Barrier Coating) with YSZ-Al₂O₃/YSZ as top coat (TC) and MCrAlY alloy as bond coat (BC) marked as YSZ-Al₂O₃/YSZ double layer TBC was used for thermal barrier material on rocket nozzle wall. Several test have been conducted (thermal test and SEM-EDX). Thermal test was divided into two part, Thermal Torch and Non-isothermal Oxidation Test which is used for measure the resistance of TBC structure against oxyacethylene flame penetration as a miniature of thermal static test for rocket nozzle until the specimen was failure and used to measure the resistance against non-isothermal oxidation as well as investigate the growth of TGO (Thermally Grown Oxide) layer on interface between TC/BC for thermal torch and non-isothermal oxidation test respectively. This test was performed at 1100^o C with 10°C/min heating rate. The results showed that the improvement of feed rate on topcoat powder gave the effect on the surface morphology of topcoat. Lower feed rate bring in a coarse surface morphology and tend to be porous. Al₂O₃/YSZ composite layer affect on the growth of TGO layer after thermal test, which indicates the lower growth of TGO especially for 15%Al₂O₃/8YSZ. TGA test showed that the sample began to oxidize at temperature range c.a 1000 – 1030°C, however 1^st derivative analysis indicated that 15% Al₂O₃/8YSZ, 14 g/min was the most stable sampel. Moreover this material has a good resistance from torch destruction.

Abstract: Researchon thepreparation of ceria based materialfor electrolyteof solid oxide fuelcellhasbeen conducted. The Sm_0.2Ce_0.8O_1.9(SDC) was prepared by sol-gel method and the layered composites of SDC with Y_0.08Zr_0.92O_3-δwerepreparedbyscreenprintingmethod.This research aims to studythecrystal structure and its conductivitycharacter. XRDmeasurementequippedwithLeBailrefinementshowsthatSDCiscrystallizedin cubic structure with space group of Fm3m.Theaddition ofYSZ into SDC does not changeitscrystal structure. However, the cell parameter of SDC is reduced from 5.434036(2) Å to 5.433(0) Å. At 600 °C, SDC has electronic conductivity that indicates the presence of electrons migration that can promotes short circuit during fuel cell operation. The combination of SDC with YSZ forming a layered composite of SDC-YSZ-SDC could reduce the electronicconductivity,eventhoughitsionicconductivityisalsobecomelowerthansingleSDCatthe same temperature.

Abstract: This research work mainly deals with the mechanical and microstructure properties of various thermal barrier coating (TBC) materials for an internal combustion engine piston using plasma spraying technique. Three thermal barrier coating Materials namely the combination of Aluminium Oxide with Titanium oxide (87%Al₂O₃ + 13%Tio₂), Aluminium Oxide with Titanium oxide (97% Al₂O₃ +3%Tio₂) and Yttria Stabilized Zirconia (YSZ) (100%) were selected and coated on Aluminium Alloy(Al Ai) with the thickness of 150 Microns (µm) for this investigation. Among three Thermal barrier coating materials, Yttria Stabilized Zirconia showed better mechanical properties such as elongation (EL) of 6.25%, tensile strength TS of 106.06MPa and yield strength (YS) of 90.34MPa when compared with that of the base piston metal Aluminium Alloy (Al Ai). Further, better microstructure properties were also observed for YSZ (100%) in comparison with other thermal barrier coated materials.

Abstract: We systematically investigated the phase transformation and grain-growth behaviors during sintering in 2 and 3 mol% Y₂O₃-stabilized tetragonal ZrO₂ (2Y and 3Y) and 8 mol% Y₂O₃-stabilized cubic ZrO₂ polycrystals (8Y). In particular, grain-boundary segregation and grain-interior distribution of Y³⁺ ions were examined by high-resolution transmission electron microscopy (HRTEM)- and scanning transmission electron microscopy (STEM)-nanoprobe X-ray energy dispersive spectroscopy (EDS) techniques. Above 1200°C, grain growth during sintering in 8Y was much faster than that in 2Y and 3Y. In the grain boundaries in these specimens, amorphous layers did not present; however, Y³⁺ ions segregated at the grain boundaries over a width of about 10 nm. The amount of segregated Y³⁺ ions in 8Y was significantly less than in 2Y and 3Y. This indicates that the amount of segregated Y³⁺ ions is related to grain growth behavior; i.e., an increase in segregated Y³⁺ ions retards grain growth. Therefore, grain-growth behavior during sintering can be reasonably explained by the solute-drag mechanism of Y³⁺ ions segregating along the grain boundary. In 2Y and 3Y, the cubic-phase regions were formed in grain interiors adjacent to the grain boundaries and/or the multiple junctions in which Y³⁺ ions segregated, which can be explained by a grain boundary segregation-induced phase transformation (GBSIPT) mechanism.

Abstract: In recent years, the key research on thermal barrier coatings (TBCs) lies in the performance improvement of materials as well as structure and process improvement, and achieves new progresses. The difficulty is application of reliability in TBCs. Researchers are exploring that employing non-destructive testing (NDT) and life prediction model on TBCs to conduct a comprehensive and real-time detection and predict the life, so as to improve the safety of TBCs in service process.

Abstract: The work is focused on the study of degradation of ZrO₂ stabilized by Y₂O₃ (YSZ) thermal barrier-coating system with CoNiCrAlY bond coat applied on cast polycrystalline nickel-based superalloy Inconel 713LC. Cylindrical specimens in as-coated conditions were cyclically strained under strain control with constant total strain amplitude in symmetrical cycle at high temperature (900 °C) in air. Coating system YSZ with CoNiCrAlY bond coat were prepared by APS method on blasted surface. The microstructure of TBC was characterized with scanning electron microscopy and energy dispersion X-ray analysis. The coating thickness and hardness profile was measured. Fracture surface, surface relief and polished sections parallel to the specimen axis were examined to study damage mechanisms in coatings under cyclic loading at high temperature. It was find that initiation of the fatigue crack usually occurs on interface YSZ-CoNiCrAlY and the trajectory of the further crack propagation was documented.

Abstract: Phase characterization is critical in material properties probing. In this study, Raman scattering was employed to identify the phase of YSZ co-doped with CeO₂/Gd₂O₃. As a comparing, XRD for co-doped YSZ was also measured. The results show that introducing a small amount of CeO₂/Gd₂O₃ into YSZ can lead to a change on Raman spectroscopy. Raman peaks appear with co-doping is attributed to the local structure change which caused by the re-distribution of vacancy. Comparing to XRD, Raman spectroscopy shows a more sensitive on the phase identify for the YSZ with a small amount dopant.

Abstract: It is well known that the martensitic transformation of YSZ from the metastable tetragonal phase (T-phase) to the monoclinic phase (M-Phase) is accelerated in hot water (especially at 473K). Trace quantities of alumina are known to aid densification, and is also exceptionally resistant to low-temperature degradation (LTD). The current contribution describes a detailed electron microscopy investigation to determine the location of trace quantities of Al2O3 in a YSZ.

Abstract: Chemical structure of hydroxyapatite (HA) is very close to human bone which makes it compatible with the tissue of the human body. Its good biocompatibility makes it to be used extensively in many prosthetic applications, especially as a porous material for optimal bone in growth. Currently, this material is being deposited on bio-inert metallic implants and used as recovery parts in human body. In this present study a high-power plasma jet known as gas tunnel type plasma torch (GTTP), was used to produce HA and YSZ reinforced HA coatings on stainless steel substrate. In this study, microstructure, tribological properties and bioactivity of the GTTP sprayed HA and YSZ reinforced HA coatings was investigated. The XRD spectra of the as-sprayed coatings showed that the as-sprayed pure HA coating retained its crystalline HA phase similar to the initial feed stock HA powder, even though there existed a possibility for occurrence of decomposition during its in-flight in high temperature plasma zone. In the present case the decomposition processes of in-flight HA could be well controlled by means of selective operating parameters and unique nature of GTTP jet. The presence of un-melted particles and pores inside the coating microstructure play a vital role in the bonding strength of the coating.