Thermal equation of state study of polymorphic phases of Y2O3
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Effects of heating rate on density, microstructure, and strength of Si3N4-6 wt.% Y2O3 and a beta-prime sialon
The effects of the heating rate during sintering/firing on the final density, microstructure, and strength of Si3N4-6 wt% Y2O3 and beta-prime sialon, sintered for four hours at 1750 C, are examined. In Si3N4-6 wt% Y2O3 increasing the heating rate from 7 C/min to 25 C/min to 90 C/min results in a corresponding decrease in the final density from 3.01 g/cu cm to 2.92 g/cu cm to 2.76 g/cu cm. In the beta-prime sialon composition all three heating rates produce an equivalent final density of 3.13 g/cu cm. All heating rates in both compositions produce nonhomogeneous microstructures. The room-temperature strength of Si3N4-6 wt% Y2O3 increases from 372 to 510 MPa with increased density, while the corresponding strengths for the betaprime sialon at equivalent densities are 345 to 445 MPa.
Campbell, S. S.↗
Strength of hot isostatically pressed and sintered reaction bonded silicon nitrides containing Y2O3
The hot isostatic pressing of reaction bonded Si3N4 containing Y2O3 produced specimens with greater room temperature strengths than those by high pressure nitrogen sintering of the same material. Average room temperature bend strengths for hot isostatically pressed reaction bonded silicon nitride and high pressure nitrogen sintered reaction bonded silicon nitride were 767 and 670 MPa, respectively. Values of 472 and 495 MPa were observed at 1370 C. For specimens of similar but lower Y2O3 content produced from Si3N4 powder using the same high pressure nitrogen sintering conditions, the room temperature strength was 664 MPa and the 1370 C strength was 402 MPa. The greater strengths of the reaction bonded silicon nitride materials in comparison to the sintered silicon nitride powder material are attributed to the combined effect of processing method and higher Y2O3 content.
William A Sanders↗
Elevated temperature creep properties of NiAl cryomilled with and without Y2O3
The creep properties of lots of NiAl cryomilled with and without Y2O3 have been determined in compression and tension. Although identical cryomilling procedures were used, differences in composition were found between the lot ground with 0.5 vol% yttria and the lot ground without Y2O3. Compression testing between 1000 and 1300 K yielded similar creep strengths for both materials, while tensile creep rupture testing indicated that the yttria-containing alloy was slightly stronger than the Y2O3-free version. Both compression and tensile testing showed two deformation regimes; whereas the stress state did not affect the high stress exponent (n approximately equals 10) mechanism, the low stress exponent regime n was approximately 6 in tension and approximately 2 in compression. The strengths in tension were somewhat less than those measured in compression, but the estimated activation energies (Q) of approximately 600 kJ/mol for tensile testing were closer to the previously measured values (approximately 700 kJ/mol) for NiAl-AlN and very different from the Q's of 400 and 200 kJ/mol for compression tests in the high and low stress exponent regimes, respectively. A Larson-Miller comparison indicated that cryomilling can produce an alloy with long-term, high-temperature strength at least equal to conventional superalloys.
Whittenberger, J. Daniel↗
The Effect of Microstructure on Mechanical Properties of Directionally Solidified Al2O3/ZrO2(Y2O3) Eutectic
The eutectic architecture of a continuous reinforcing phase within a higher volume fraction phase or matrix can be described as a naturally occurring in-situ composite. Here we report the results of experiments aimed at identifying the sources of high temperature creep resistance and high levels of strength in a two phase Al2O3/ZrO2(Y2O3) system. The mechanical properties of two phase Al2O3/ZrO2(Y2O3) eutectic are superior to those of either constituent alone due to strong constraining effects provided by the coherent interfaces and microstructure. The AlO3/ZrO2(Y2O3) eutectic maintains a low energy interface resulting from directional solidification and can produce strong and stable reinforcing phase/matrix bonding. The phases comprising a eutectic are thermodynamically compatible at higher homologous temperatures than man-made composites and as such offer the potential for superior high temperature properties.
Sayir, Ali↗
Calculation of Phase Equilibria in the Y2O3-Yb2O3-ZrO2 System
Rare earth oxide stabilized zirconias find a wide range of applications. An understanding of phase equilibria is essential to all applications. In this study, the available phase boundary data and thermodynamic data is collected and assessed. Calphad-type databases are developed to completely describe the Y2O3-ZrO2, Yb2O3-ZrO2, and Y2O3-Yb2O3 systems. The oxide units are treated as components and regular and subregular solution models are used. The resultant calculated phase diagrams show good agreement with the experimental data. Then the binaries are combined to form the database for the Y2O3-Yb2O3-ZrO2 psuedo-ternary.
Jacobson, Nathan S.↗
Thermodynamic Assessment of the Y2o3-yb2o3-zro2 System
Yttria-zirconia (Y2O3-ZrO2) is the most widely used of the rare earth oxide-zirconia systems. There are numerous experimental studies of the phase boundaries in this system. In this paper, we assess these data and derive parameters for the solution models in this system. There is current interest in other rare earth oxide-zirconia systems as well as systems with several rare earth oxides and zirconia, which may offer improved properties over the Y2O3-ZrO2 system. For this reason, we also assess the ytterbia-zirconia (Yb2O3-ZrO2) and Y2O3-Yb2O3-ZrO2 system.
Jacobson, Nathan S.↗
Thermal Conductivity and Stability of HfO2-Y2O3 and La2Zr2O7 Evaluated for 1650 Deg C Thermal/Environmental Barrier Coating Applications
HfO2-Y2O3 and La2Zr2O7 are candidate thermal and environmental barrier coating (T/EBC) materials for gas turbine ceramic matrix composite (CMC) combustor applications because of their relatively low thermal conductivity and high temperature capability. In this paper, thermal conductivity and high temperature stability of hot-pressed and plasma sprayed specimens with representative partially-stabilized and fully-cubic HfO2-Y2O3 compositions and La2Zr2O7 were evaluated at temperatures up to 1700 C using a steady-state laser heat-flux technique. Sintering behavior of the plasmasprayed coatings was determined by monitoring the thermal conductivity increases during a 20-hour test period at various temperatures. Durability and failure mechanisms of the HfO2-Y2O3 and La2Zr2O7 coatings on mullite/SiC hexoloy or SiC/SiC CMC substrates were investigated at 1650 C under thermal gradient cyclic conditions. Coating design and testing issues for the 1650 C thermal/environmental barrier coating applications are also discussed.
Zhu, Dong-Ming↗
Thermal Conductivity and Temperature Limits of Electron-Beam Physical-Vapor-Deposited ZrO2-7wt%Y2O3 Thermal Barrier Coating
The electron-beam physical-vapor-deposited (EB-PVD) ZrO2-7wt%Y2O3 thermal barrier coating has been widely used to protect engine hot section components in modem aircraft engines. Thermal conductivity and the conductivity increases due to sintering and phase changes are important coating design parameters. There is a need to characterize the coating thermal conductivity behavior and temperature limits, in order to potentially take full advantage of the coating capability. In addition, since the ZrO2-7wt%Y2O3 coating is often used as a baseline coating for the development of advanced lower thermal conductivity and higher temperature capability coatings, a thorough evaluation of the coating conductivity behavior at future higher engine operating temperatures will be useful for more accurately assessing the benefit gained from the new coating systems. In this study, thermal conductivity behavior of EB-PVD ZrO2-7wt%Y2O3 coating has been systematically investigated as a function of temperature (up to 2600 F) and time under steady-state and cyclic test conditions using a laser heat-flux technique. Thermal conductivity change kinetics were determined under realistic engine high temperature thermal gradient conditions, and correlated to the coating microstructural and phase changes. The thermal conductivity prediction models have been established in terms of heat flux, time, and testing temperatures.
Zhu, Dongming↗
Effect of thermal cycling on ZrO2-Y2O3 thermal barrier coatings
The paper studies the comparative life of plasma-sprayed ZrO2-Y2O3 thermal barrier coatings on NiCrAlY bond coats on Rene 41 in short (4 min) and long (57 min) thermal cycles at 1040 C in a 0.3-Mach flame. Attention is given to determining the effect of short- and long-duration cycles on ZrO2-Y2O3 coatings, the cause of any cycle frequency effects, and methods to improve tolerance to thermal stress. Short cycles greatly reduced the life of the ceramic coating in terms of time at temperatures as compared to longer cycles, the failed coating indicating compressive failure. The experiments and stress calculations show that repeatedly subjecting a ceramic coating to high rates of initial heating has a more destructive influence on the coating than sustained operation at temperature. The effect of such thermal compressive stresses might be minimized through coating deposition and thickness control and by turbine cycle measurement to keep starting heating rates below critical values.
Mcdonald, G.↗
Effect of CeO2, MgO and Y2O3 additions on the sinterability of a milled Si3N4 with 14.5 wt% SiO2
The sinterability of alpha Si3N4 with 0-5.07 equivalent per cent of CeO2, MgO, or Y2O3 has been studied in the temperature range 1650-1820 C by density measurements and X-ray diffraction analysis. Maximum densities were obtained in the range 1765-1820 C and were 99.6% of theoretical with 2.5% CeO2; 98.5% of theoretical with 1.24 to 1.87% MgO, and 99.2% of theoretical with 2.5% Y2O3. Densities 94% or more of theoretical value were obtained with as little as 0.62 equivalent per cent additive.
Arias, A.↗
Effect of fuel to air ratio on Mach 0.3 burner rig hot corrosion of ZrO2-Y2O3 thermal barrier coatings
A Mach 0.3 burner rig test program was conducted to determine how the fuel to air mass ratio affects the durability of ZrO2-Y2O3/Ni-16Cr-6Al-0.31Y thermal barrier coating systems in combustion products containing 5 ppm Na and 2 ppm V. As the fuel to air mass ratio was increased from 0.039 to 0.049, the durability of ZrO2-6Y2O3, ZrO2-8Y2O3 and ZrO2-12Y2O3 coatings decreased. ZrO2-8Y2O3 coatings were approximately 2X and 1.3X more durable than ZrO2-12Y2O3 and ZrO2-6Y2O3 coatings respectively at the fuel to air mass ratio of 0.039. The number of one hour cycles endured by ZrO2-8Y2O3 coatings varied from averages of 53 to 200 for the fuel to air mass ratios of 0.049 and 0.039, respectively. At the fuel to air mass ratio of 0.049, all ZrO2-Y2O3 coated specimens failed in 40 to 60 one hour cycles
Hodge, P. E.↗
Sintering, properties and fabrication of Si3N4 + Y2O3 based ceramics
Pure silicon nitride shows a remarkable resistance to sintering without the use of densification additives. The present investigation is concerned with results which show the effect of chemical content on sinterability, taking into account the composition, raw material impurities, and processing contaminants. Aspects of sintering are discussed along with strength characteristics, and oxidation relations. Attention is given to phase field I and II materials, phase field III and IV materials, tungsten carbide and oxidation at 600 C, and studies involving shape fabrication by injection molding. It was found that in sintering Si3N4 + Y2O3 an increase in the amount of Y2O3 and, in particular, the addition of Al2O3 enhances the fluidity of the liquid phase.
Quackenbush, C. L.↗
Analysis of grain boundary phase devitrification of Y2O3- and Al2O3-doped Si3N4
The present study has the objective to show that a Fourier Transform IR (FTIR) spectrometer in a single-beam reflection mode can be used for direct comparison of fractured vs nonfractured Si3N4 surfaces. This can be done because the FTIR method permits a digital summation of nearly 1000 scans of the fracture surface. Commercial-grade Si3N4, Y2O3, and Al2O3 were used in the study. The samples were heat treated in a vacuum induction heating furnace at either 1000 C for 10 h or 1200 C for 10 h each. Use of Fourier transform IR reflection spectroscopic analysis and X-ray diffraction shows that 10 h at 1200 C is sufficient to devitrify the amorphous grain boundary phase of Si3N4 containing 15 percent Y2O3 + 2 percent Al2O3 densification aids.
Hench, L. L.↗
Materials Data on Y2O3 by Materials Project
Y2O3 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Y3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Y–O bond distances ranging from 2.22–2.59 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Y3+ atoms to form OY4 tetrahedra that share corners with six equivalent OY6 octahedra, corners with six equivalent OY4 tetrahedra, edges with three equivalent OY6 octahedra, and edges with three equivalent OY4 tetrahedra. The corner-sharing octahedra tilt angles range from 19–55°. In the second O2- site, O2- is bonded to six equivalent Y3+ atoms to form OY6 octahedra that share corners with twelve equivalent OY4 tetrahedra, edges with six equivalent OY6 octahedra, and edges with six equivalent OY4 tetrahedra.
36 MATERIALS SCIENCE↗
Materials Data on Y2O3 by Materials Project
Y2O3 is Corundum-like structured and crystallizes in the cubic Ia-3 space group. The structure is three-dimensional. there are two inequivalent Y3+ sites. In the first Y3+ site, Y3+ is bonded to six equivalent O2- atoms to form a mixture of distorted edge and corner-sharing YO6 octahedra. The corner-sharing octahedra tilt angles range from 54–56°. There are a spread of Y–O bond distances ranging from 2.27–2.36 Å. In the second Y3+ site, Y3+ is bonded to six equivalent O2- atoms to form a mixture of edge and corner-sharing YO6 octahedra. The corner-sharing octahedral tilt angles are 56°. All Y–O bond lengths are 2.31 Å. O2- is bonded to four Y3+ atoms to form a mixture of distorted edge and corner-sharing OY4 trigonal pyramids.
36 MATERIALS SCIENCE↗
Materials Data on Y2O3 by Materials Project
Y2O3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Y3+ sites. In the first Y3+ site, Y3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Y–O bond distances ranging from 2.25–2.59 Å. In the second Y3+ site, Y3+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing YO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Y–O bond distances ranging from 2.21–2.48 Å. In the third Y3+ site, Y3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Y–O bond distances ranging from 2.26–2.75 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded to five Y3+ atoms to form distorted OY5 square pyramids that share corners with seven OY4 tetrahedra, corners with two equivalent OY4 trigonal pyramids, edges with two equivalent OY6 octahedra, edges with two equivalent OY5 square pyramids, edges with three OY4 tetrahedra, and edges with three equivalent OY4 trigonal pyramids. In the second O2- site, O2- is bonded to four Y3+ atoms to form OY4 tetrahedra that share a cornercorner with one OY6 octahedra, corners with five equivalent OY5 square pyramids, corners with four OY4 tetrahedra, corners with three equivalent OY4 trigonal pyramids, edges with two equivalent OY6 octahedra, an edgeedge with one OY5 square pyramid, and edges with two equivalent OY4 tetrahedra. The corner-sharing octahedral tilt angles are 49°. In the third O2- site, O2- is bonded to four Y3+ atoms to form distorted OY4 trigonal pyramids that share a cornercorner with one OY6 octahedra, corners with two equivalent OY5 square pyramids, corners with nine OY4 tetrahedra, corners with two equivalent OY4 trigonal pyramids, edges with three equivalent OY5 square pyramids, and edges with two equivalent OY4 trigonal pyramids. The corner-sharing octahedral tilt angles are 37°. In the fourth O2- site, O2- is bonded to four Y3+ atoms to form distorted OY4 tetrahedra that share corners with two equivalent OY6 octahedra, corners with two equivalent OY5 square pyramids, corners with four OY4 tetrahedra, corners with six equivalent OY4 trigonal pyramids, an edgeedge with one OY6 octahedra, edges with two equivalent OY5 square pyramids, and an edgeedge with one OY4 tetrahedra. The corner-sharing octahedral tilt angles are 13°. In the fifth O2- site, O2- is bonded to six Y3+ atoms to form OY6 octahedra that share corners with six OY4 tetrahedra, corners with two equivalent OY4 trigonal pyramids, edges with two equivalent OY6 octahedra, edges with four equivalent OY5 square pyramids, and edges with six OY4 tetrahedra.
36 MATERIALS SCIENCE↗
Materials Data on Y2O3 by Materials Project
Y2O3 crystallizes in the cubic Pn-3m space group. The structure is three-dimensional. Y3+ is bonded in a 6-coordinate geometry to six equivalent O2- atoms. All Y–O bond lengths are 2.29 Å. O2- is bonded to four equivalent Y3+ atoms to form a mixture of corner and edge-sharing OY4 tetrahedra.
36 MATERIALS SCIENCE↗