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The current study reports the fabrication of (1- x) Y 3 Al 5 O 12 / x LaPO 4 (x = 0, 0.1, 0.2, 0.3, 0.4) composites and their evaluation against molten V 2 O 5 corrosion at 900 °C and 1000 °C for 20 h. The phase compositions and microstructures of the samples were analysed using X-ray diffraction (XRD) spectroscopy, as well as scanning electron microscopy (SEM), both before and after the corrosion tests. The yttrium aluminium garnet (Y 3 Al 5 O 12 , YAG) was easily corroded by molten V 2 O 5 , with the primary product being YVO 4. While LaPO 4 exhibited perfect resistance to the molten V 2 O 5 corrosion, it was ineffective at improving the corrosion resistance of the YAG/LaPO 4 composite materials. However, the LaPO 4 /YAG double layers materials prepared with LaPO 4 coated on the surface of YAG exhibit excellent resistance to molten V 2 O 5 , owing to the formation of the P diffusion layer at the interface between the LaPO 4 and YAG, which acts as a sealing layer, preventing the molten V 2 O 5 from penetrating. [ABSTRACT FROM AUTHOR]

As a toughening agent, LaPO 4 has been used to improve several properties of ceramics. In such applications, its compatibility with the matrix material should be considered first. In this study, the compatibility of LaPO 4 and magnesium lanthanum hexa-aluminate (LaMgAl 11 O 19 , LMA) was elucidated at temperatures ranging from room temperature to 1600 °C. The compositions, thermal stabilities, thermal conductivities and microstructures of the above-mentioned materials were analysed using X-ray diffraction, thermogravimetry-differential scanning calorimetry, thermal conductivity tester and scanning electron microscopy. The results indicated that the two materials maintained a good compatibility at temperatures lower than 1600 °C. At 1600 °C, the diffusion of La was observed to alter the chemical composition of LaPO 4 and accelerate its reaction with LMA, leading to the formation of LaAlO 3 and magnesium lanthanum aluminium oxide, resulting in the increase of thermal conductivity. [ABSTRACT FROM AUTHOR]

In this work, porous LaMgAl 11 O 19 (LMA) thermal barrier coatings (TBCs) were deposited by atmospheric plasma spraying, using the powder mixtures LMA/graphite with different weight fractions. The effects of graphite contained in the powder mixtures on the amorphous phase content, microstructure and porosity of the coatings were investigated using X-ray diffraction and scanning electron microscopy. The mechanical properties, such as bonding strength, micro-hardness and fracture toughness, and the thermal cycling behavior of the coatings were investigated. Results indicated that the amorphous phase content and the porosity of the coatings increased with the increase of graphite content in the powder mixtures, whereas the bonding strength and the micro-hardness exhibited an opposite trend. Thermal cycling lifetimes of the coatings decreased with the increase of graphite content, owing to the increase of amorphous phase content and the decrease of the bonding strength. Failure of the coatings was mainly caused by the thermal expansion mismatch and growth of thermally grown oxides. [ABSTRACT FROM AUTHOR]

ZrO 2 co-stabilized by CeO 2 and TiO 2 with stable, nontransformable tetragonal phase has attracted much attention as a potential material for thermal barrier coatings (TBCs) applied at temperatures > 1200 °C. In this study, ZrO 2 co-stabilized by 15 mol% CeO 2 and 5 mol% TiO 2 (CTZ) and CTZ/YSZ (zirconia stabilized by 7.4 wt% Y 2 O 3 ) double-ceramic-layer TBCs were respectively deposited by atmospheric plasma spraying. The microstructures, phase stability and thermo-physical properties of the CTZ coating were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric-differential scanning calorimeter (TG-DSC), laser pulses and dilatometry. Results showed that the CTZ coating with single tetragonal phase was more stable than the YSZ coating during isothermal heat-treatment at 1300 °C. The CTZ coating had a lower thermal conductivity than that of YSZ coating, decreasing from 0.89 W m −1 K −1 to 0.76 W m −1 K −1 with increasing temperature from room temperature to 1000 °C. The thermal expansion coefficients were in the range of 8.98 × 10 −6 K −1 – 9.88 ×10 −6 K −1 . Samples were also thermally cycled at 1000 °C and 1100 °C. Failure of the TBCs was mainly a result of the thermal expansion mismatch between CTZ coating and superallloy substrate, the severe coating sintering and the reduction-oxidation of cerium oxide. The thermal durability of the TBCs at 1000 °C can be effectively enhanced by using a YSZ buffer layer, while the thermal cycling life of CTZ/YSZ double-ceramic-layer TBCs at 1100 °C was still unsatisfying. The thermal shock resistance of the CTZ coating should be improved; otherwise the promising properties of CTZ could not be transferred to a well-functioning coating. [ABSTRACT FROM AUTHOR]

Nanostructured yttria stabilized zirconia (n-YSZ) thermal barrier coatings were fabricated by atmospheric plasma spraying (APS) at different spraying powers. The microstructures, phase stability and mechanical properties of the n-YSZ coatings were examined by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Vickers indentation, respectively. The adhesion strength of coatings was evaluated according to ASTM C633-01 standard. Thermal cyclic oxidation method was carried out to study the effect of spraying power on thermal shock resistance of the coatings. Results showed that the n-YSZ coatings had a bimodal microstructure consisting of well melted splats and partially melted nanostructured areas. Both the porosity and the content of nanostructure in n-YSZ coatings decreased with increasing of the spraying power. After heat treatment at 1573 K, the porosity of the coating decreased and the hardness increased noticeably compared with that of the as-sprayed coating, indicating the sintering effect of the nanostructured coating. However, porosity of the coating deposited by the lowest spraying power (22 kW) still retain above 10% after annealing at 1573 K for 24 h, showing higher sintering resistant ability. Although phase structures certainly changed during heat treatment, phase compositions were more stable for the coatings deposited by the relatively low spraying powers. The average bond strength and thermal cycling life of the coating prepared by the lowest spraying power (22 kW) were about 29 MPa and 292 cycles, respectively, which were approximately twice as much as those of the coating deposited by the highest spraying power (42 kW). The best thermal shock resistance obtained for the n-YSZ coatings prepared at 22 kW can be partially attributed to its high content of nanozones, which play an important role in reducing the oxygen diffusion, releasing the thermal stress and interrupting crack propagation. [ABSTRACT FROM AUTHOR]

Alumina based rare earth oxides ceramic materials, with the good performance against the CMAS corrosion, were widely used as the thermal/environmental barrier coatings. In this work, three Y 2 O 3 –Al 2 O 3 binary ceramic bulks, which were the Y 3 Al 5 O 12 , YAlO 3 and Y 4 Al 2 O 9 , were prepared by high temperature solid state reaction using the Y 2 O 3 and Al 2 O 3 as the raw materials. The resistances to CMAS corrosion of these materials at 1250 °C and 1350 °C were compared fully. The compositions and structures of the samples before and after corrosion were analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results showed that the different chemical compositions of the materials resulted in the different optical basicity (OB) values which can decide the reactivity of the material with the CMAS melts. The Y 3 Al 5 O 12 ceramic material was inert to the CMAS for its low OB value of 0.75 and damaged seriously by the CMAS through physical penetration. The YAlO 3 and Y 4 Al 2 O 9 with the high OB values of 0.80 and 0.87 reacted with the CMAS to form the Ca 4 Y 6 (SiO 4) 6 O. The YAlO 3 ceramic bulk exhibited the good performance against the CMAS corrosion benefitting from the formation of the Ca 4 Y 6 (SiO 4) 6 O and the CaAl 2 Si 2 O 8. [ABSTRACT FROM AUTHOR]

In this study, the destabilization resistance of Sc 2 O 3 and CeO 2 co-stabilized ZrO 2 (SCZ) ceramics was tested in Na 2 SO 4 + V 2 O 5 molten salts at 750°C–1100 °C. The phase structure and microstructure evolution of the samples during the hot corrosion testing were analyzed with X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS), and X-ray photoelectron spectroscopy (XPS). Results showed that the destabilization of SCZ ceramics at 750 °C was the result of the chemical reaction with V 2 O 5 to produce m-ZrO 2 and CeVO 4 , and little ScVO 4 was detected in the Sc 2 O 3 -rich SCZ ceramics. The primary corrosion products at 900 °C and 1100 °C were CeO 2 and m-ZrO 2 due to the mineralization effect. The Sc 2 O 3 -rich SCZ ceramics exhibited excellent degradation resistance and phase stability owing to the enhanced bond strength and the decreased size misfit between Zr4+ and Sc3+. The destabilization mechanism of SCZ ceramic under hot corrosion was also discussed. [ABSTRACT FROM AUTHOR]