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1.
The influence of Er_2 O_3 addition on the phase evolution and mechanical properties of sintered(1600 ℃,4 h) ZTA(yttria stabilized zirconia toughened alumina)-TiO_2 composites was investigated. The SEM and XRD results reveal the formation of a new erbium zirconium oxide,Zr_3 Er_4 O_(12),with a granulate morphology when Er_2 O_3 content is higher than 1 wt%. The grain sizes of both Al_2 O_3 and yttria-stabilized zirconia phases decrease with an increase in the Er_2 O_3 content. The relative density, Vickers hardness and fracture toughness of the composites are found to be strongly dependent on their grain sizes, relative densities and the formation of the Zr_3 Er_4 O_(12) secondary phases. The composite with 5 wt% Er_2 O_3 shows the highest relative density(99.93%), Vickers hardness(1752 HV) and fracture toughness(7.92 MPa·m~(1/2)). 相似文献
2.
The process to prepare pure phase of hexagonal Y2O2S was investigated. Effect of mixed flux of Na2CO3 and S amounts was studied. The phase composition and morphology were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the single phase of Y2O2S with smooth morphology could not be obtained as the molar ratio of Y2O3, Na2CO3 and S was in the range of 1:(0.5-1):(2-3) until the molar ratio was increased to 1:1.5:4. Different Er3+ concentration doped Y2O2S... 相似文献
3.
ZrO 2 containing 2% (mol fraction) Y 2O 3 and 3% (mol fraction) Y 2O 3 were added into Al 2O 3 matrix, compositing composites with 15% volume fraction of addictives mentioned above. The testing of property and analysis of SEM presented that, after vacuum sintering at 1550 °C, thermal shock resistance of two composites was superior to Al 2O 3 ceramic. The experiment showed that the properties of Al 2O 3 composites was higher than Al 2O 3 ceramic, and Al 2O 3/ZrO 2(3Y) was higher than Al 2O 3/ZrO 2(2Y) in thermal shock resistance. Improvement of thermal shock resistance of composites was attributed to many toughness machanisms of ZrO 2(Y 2O 3). By calculation, the fracture energy of Al 2O 3, Al 2O 3/ZrO 2 (2Y) and Al 2O 3/ZrO 2(3Y) was 38100.8 and 126.2 J·m −2, respectively. Cracks initiation resistance (R') of Al 2O 3/ZrO 2(3Y) and Al 2O 3/ZrO 2(2Y) was higher than Al 2O 3 ceramic by 1.57 and 1.41 time, respectively, and cracks propagation resistance (R″″) was higher than Al 2O 3 ceramic by 1.46 and 1.38 time, respectively, which was corresponding to the results of residual strength. 相似文献
4.
Er xTi 0.1Zr 0.9–xO 2–1.5x ( x = 0.04, 0.05, 0.06, 0.07, 0.08) ceramics were synthesized by a solid-state reaction method. The influence of the Er 3+ addition on the phase composition, Vickers hardness, fracture toughness, and thermal conductivity of this ceramic material was investigated. The X-ray diffraction results reveal that the c-ZrO 2 content increases from 1.85 vol% to 33.89 vol%, and the percentage of t-ZrO 2 decreases from 98.15 vol% to 66.11 vol% with the increase in Er 3+ content from 4 mol% to 8 mol%. Moreover, the addition of Er 3+ is beneficial to the volume expansion of the unit cell. At the same time, the incorporation of Er 3+ weakens the coordination of oxygen ions around the metal cations, resulting in a corresponding decrease in the tetragonality of the t-ZrO 2. The Vickers hardness and fracture toughness of the Er xTi 0.1Zr 0.9–xO 2–1.5x ceramics show increasing and decreasing trends, respectively. The thermal conductivity has a significant decline due to point defects caused by the Er 3+ doping. The 8ETZ ceramic exhibits the highest Vickers hardness (12.7 GPa), the lowest fracture toughness (7.6 MPa?m 1/2), and the lowest average thermal conductivity (1.85 W/(m·K)) in the temperature range of 200–1000 °C. All of the above properties are higher than those of the Y 2O 3-stabilized ZrO 2 ceramic. 相似文献
5.
We studied the reactions of Ti and Zr with AlN, 99.8% Al 2O 3 and 95% Al 2O 3. The substrates were chosen to represent a simple nitride (AlN), a simple oxide (99.8% Al 2O 3), and a simple oxide with a silicate grain boundary phase (95% Al 2O 3). The activities of the Ti and the Zr were varied by dissolving them at 1 and 5 wt% in the 72 Ag-28 Cu eutectic composition, which is otherwise unreactive with the ceramics. Reactions were studied by measuring the variation of the alloy contact angle on the ceramic with time at temperature and by determining the compositions of interfacial reaction products. Contact angles were lower for Ti alloys than for those containing Zr. Reaction products were primarily the nitrides of Zr and Ti for reaction with AlN and the respective oxides for reaction with Al 2O 3. Complex alloy phases were found in the metal away from the ceramic-metal reaction zone. 相似文献
6.
Conclusions An investigation into the creep of Al 2O 3-AlN and Y 2O 3-AlN ceramics has demostrated that the addition of 20–80% AlN reduces the creep rate of Al 2O 3. In the system Y 2O 3-AlN the existence of a creep rate maximum has been discovered, which may be a manifestation of structural superplasticity.Translated from Poroshkovaya Metallurgiya, No. 2(158), pp. 76–82, February, 1976.The authors wish to thank Prof. R. A. Andrievskii for his interest in this work. 相似文献
7.
BaO-Y 2O 3-TiO 2 microwave dielectric ceramics with the rich area of TiO 2 were fabricated by a solid-state reaction method using BaCO 3, Y 2O 3, TiO 2 powders as starting materials. The sintering characteristics, phase composition, micro-structures and microwave dielectric properties of BaO-Y 2O 3-TiO 2 microwave dielectric ceramics with different k values sintered at different temperatures were investigated. The results showed that the sintering temperature of BaO-Y 2O 3-TiO 2 microwave dielectric ceramics was lower (about 1240 °C), and the sintered ceramics with the major phase of Y 2Ti 2O 7 had excellent dielectric properties. When k = 4, ɛ r and tanδ were about 78.3 and 3 × 10 −3 respectively. When k=5, ɛ r and tanδ were about 53 and 9 × 10 −4 respectively. 相似文献
8.
The present paper discussed some fundamental aspects on composite oxide scales and coatings for protection of alloys from high temperature oxidation, the related thermodynamic conditions, special mechanical characteristics and a sealing mechanism. It was proposed that the oxide scales and coatings with a composite structure should possess superior mechanical properties than that with a single phase oxide. It also showed that the Al2O3 scales or coatings doped with Y2O3 and ZrO2 (or YSZ)-Al2O3 composite coatings possessed superior properties at high temperatures. In such composite oxide scales and coatings, the fracture resistance of the scales was increased by the toughening effect, the thermal stress was decreased owing to the increase of thermal-expansion coefficients, and Al2O3 phase could seal the alloy substrate well. In addition, the kinetic equation of thermal growth oxide on alloy covered with composite oxide coatings was derived. 相似文献
9.
To prepare ytterbium doped lanthania yttria nanopowder a method of laser evaporation of mixed oxides was used. After calcinations of the powder at 1200 °C a pure single-phase solid solution Yb3+:(LaxY1–x)2O3 was formed in the nanoparticles. Influence of lanthanum oxide as an isovalent additive on the yttria structure was investigated. The lanthanium ions were proved to be a good aid to sinter yttria ceramics doped with Yb3+ at moderate temperatures about 1650 °С. The ceramics with relative density higher than 99.99% and grain size about 40 μm were fabricated. Full transmittance of 1.8 mm thick Yb0.11La0.23Y1.66O3 ceramics reached 82.5% at 800 nm. This material could be a good gain medium for ytterbium high power pulse lasers. 相似文献
10.
The effect of scandium oxide additions on the emission properties of impregnated tungsten cathodes was investigated. The synthesis of alumoscandates in the BaO ― CaO ― Sc2O3 ― Al2O3 system were studied by x-ray diffraction, thermography, and petrographic analysis. The hygroscopic properties of the emission-active material was determined. Based on the results of emission tests the recommended optimal compositions of emission-active material are 2.4 BaO·0.6 CaO·0.1 Sc2O3·0.9 Al2O3 and 2.6 BaO·1.9 CaO·0.1 Sc2O3·0.9 Al2O3. Cathodes based on these compositions had lifetimes greater than 10000 h operating in the temperature range 900-1000°C at current densities of 15-20 A/cm2 in a vacuum of the order of 10−6 Torr. 相似文献
11.
Rare earth Er 3+ doped (Sm 1–xEr x) 2Zr 2O 7 ( x = 0.1, 0.2, and 0.3) ceramic samples were synthesized using a solid state reaction method. The microstructure and thermal properties of these ceramics were investigated to evaluate their potential as thermal barrier coating materials. The results show that ceramics are compact with regular-shaped grains of 1–5 μm size. (Sm 1–xEr x) 2Zr 2O 7 has a pyrochlore structure mainly determined by ionic radius ratio, but the ordering degree decreases with increase of the Er 2O 3 content. There is no phase transformation from 1000 to 1200 °C, and the (Sm 1–xEr x) 2Zr 2O 7 ceramics exhibit excellent phase stability during thermal treatment at 1200 °C for 100 h and 1400 °C for 50 h. The thermal conductivities of dense (Sm 1–xEr x) 2Zr 2O 7 ceramics range from 1.52 to 1.59 W/(m·K), which is lower than that of Sm 2Zr 2O 7, and decrease as the Er 2O 3 content increases. Besides, the thermal expansion coefficient of (Sm 1–xEr x) 2Zr 2O 7 is higher than that of Sm 2Zr 2O 7. 相似文献
12.
The influence of Dy 2O 3 doping on the properties of medium temperature sintering (Ba, Sr)TiO 3 series capacitor ceramics was studied by single factor various amount method, and the law of the influence on the medium temperature sintering (Ba, Sr)TiO 3 series capacitor ceramics was obtained. The dielectric materials used for multilayer ceramic capacitor was obtained, of which the dielectric constant was 1375, the dielectric loss was 0.0060, the density was 5.92 g·cm −3, the sintering temperature was less than 1150 °C, the capacitance temperature changing rate (Δ C/C) was less than ± 15%, the voltage withstand strength was more than 9.3 kV·mm −1, and the crystal grain size was about 1 μm. The surface morphology of the sample doped with various amount Dy 2O 3 was analyzed by scanning electron microscope (SEM). The results showed that doping Dy 2O 3 could form defect solid solution, stop grain growth, fine crystal grain, widen curie peak, obtaining high dielectric constant and low dielectric loss, capacitance temperature property was suited for X7R character, in the (Ba,Sr)TiO 3 series ceramics. At the same time, the voltage withstand strength was enhanced greatly. 相似文献
13.
Studies have been made on the changes in structure and properties of sintered materials: Si 3N 4 - 5 mass% Y 2O 3 - 2 mass% Al 2O 3, Si 3N 4 - 5 mass% Y 2O 3 - 5 mass% Al 2O 3, and Si 3N 4 - 40 mass% TiN on deformation in a high-pressure chamber of toroid type (pressure 4–5 GPa, temperature 1000–1600 °C), and also by direct extrusion with degrees of reduction of 55 and 72% (temperature 1750–1850 °C, pressure on the plunger 20–30 MPa). After pressure-chamber treatment, the materials have elevated mechanical characteristics: HV 10 ≈ 16.7 GPa, K Ic up to 8.4 MPa · m 1/2 for the system Si 3N 4 - Y 2O 3 - Al 2O 3; and HV 10 ≈ 16.9 GPa, K Ic up to 9.4 MPa · m 1/2 for Si 3N 4 - TiN. A structure feature is the small size of the coherent-scattering regions: 51 nm for Si 3N 4 and 65 nm for TiN in the system Si 3N 4 - TiN, and 33 nm for specimens in the system Si 3N 4 - Y 2O 3 - Al 2O 3. High-temperature extrusion results in a structure with β-Si 3N 4 grains elongated along the deformation direction. The anisotropic structure has K Ic values in directions perpendicular to and parallel to the direction of extrusion of 11.5–12.0 MPa · m 1/2 and 7.5–7.8 MPa · m 1/2, respectively. The hardness after extrusion becomes 16.0 GPa. 相似文献
14.
A monolithic FeAl 3-Fe 2Al 5 alloy exhibited a predominantly transgranular cleavage fracture mode and a fracture toughness value of about 1.1 MPa m 1/2 at room temperature. It is suggested that the low fracture toughness value for the alloy is a result of its complex crystal structure (intrinsic). The incorporation of 10 vol % Al 2O 3 or Y 2O 3 particles into the matrix increased the fracture toughness to 3.4 to 3.8 MPa m 1/2. The increase in fracture toughness is attributed to crack deflection by the particles. As a result, due to their excellent high temperature creep strength and oxidation resistance coupled with low material costs, intermetallics based upon FeAl 2, Fe 2Al 5 and FeAl 3 may be excellent candidates for high temperature applications if their ductility and toughness at room temperature can be improved. 相似文献
15.
Er was used as a dopant for the first time in preparing conductive powder to improve its performance. Er and Sb doped SnO 2 conductive nanoparticles were prepared by the complexation-coprecipitation method with Sn, Sb 2O 3 and Er 2O 3 as the raw materials. Thermal behavior, crystal phase, and structure of the prepared conductive nanoparticles were characterized by TG/DSC, FTIR, XRD and TEM techniques, respectively. The resistivity of the prepared conductive nanoparticles was 0.29 Ω·cm; TG/DSC curves showed that the precursors lost weight completely before 750 °C; FTIR spectrum showed that the vibration peak were wide peak in 711 × 600 cm −1; the Er and Sb doped SnO 2 conductive nanoparticles had intense absorption in 4000 × 1600 cm −1; Er and Sb doped SnO 2 had a structure of tetragonal rutile; complex doping was achieved well by complexation-coprecipitation method and was recognized as replacement doping or caulking doping; TME showed that the particles were weakly agglomerated, the size of the particles calcined at 800 °C ranged approximately from 10 to 30 nm. 相似文献
16.
Friction and wear are studied for materials of the system TiN — AlN preliminary oxidized at 800–1100°C. It was established
that thin oxide films containing Al 2TiO 5 and α-Al 2O 3, that promote a decrease in frictional wear, form on the surface of composite materials of the system TiN — AlN. Our assumptions
are confirmed that the improvement in tribological properties of TiN — AlN composites is caused by forming oxide screening
layers that prevent direct contact between the ceramics and steel counter-body. At high rates (V=16 m/sec) and pressure (P=2.0
MPa) the oxide films form more rapidly.
Translated from Poroshkovaya Metallurgiya, Nos. 1–2(411), pp. 121–124, January–February, 2000. 相似文献
17.
Nickel-20 wt pet chromium alloys containing ThO 2, Y 2O 3, La 2O 3, Al 2O 3 and Li 2O, as prepared by the mechanical alloying technique, were examined for isothermal and cyclic oxidation resistance in dry air
at 1000, 1100 and 1200°C. TDNiCr, a commercial electrical heating element alloy (Com Ni-20Cr) and a laboratory melted alloy 9Lab Ni-20Cr) were also tested. It was found that Y 2O 3, La 2O 3, Al 2O 3 and ThO 2 dispersoids markedly increased both isothermal and cyclic oxidation resistance compared to Lab Ni-20Cr at all temperatures;
in contrast Li 2O additions gave no improvement in protection. Com Ni-20Cr was in between Lab Ni-20Cr and the Y 2O 3, A1 2O 3 and ThO 2 containing alloys in both cyclic and isothermal oxidation performance. A mechanism based on alterations in the defect structure
of Cr 2O 3 is proposed to explain these dispersed oxide effects on isothermal oxidation behavior. It is based on a reduction in cation
transport rates which in turn alter the rate of oxide growth. ThO 2-containing alloys fabricated by the mechanical alloying technique were found to have oxidation resistance fully equal to
commercial TDNiCr. Com Ni-20Cr performed better than Lab Ni-20Cr, but not as well as TDNiCr. 相似文献
18.
Nickel-20 wt pet chromium alloys containing ThO 2, Y 2O 3, La 2O 3, Al 2O 3 and Li 2O, as prepared by the mechanical alloying technique, were examined for isothermal and cyclic oxidation resistance in dry air at 1000, 1100 and 1200°C. TDNiCr, a commercial electrical heating element alloy (Com Ni-20Cr) and a laboratory melted alloy 9Lab Ni-20Cr) were also tested. It was found that Y 2O 3, La 2O 3, Al 2O 3 and ThO 2 dispersoids markedly increased both isothermal and cyclic oxidation resistance compared to Lab Ni-20Cr at all temperatures; in contrast Li 2O additions gave no improvement in protection. Com Ni-20Cr was in between Lab Ni-20Cr and the Y 2O 3, A1 2O 3 and ThO 2 containing alloys in both cyclic and isothermal oxidation performance. A mechanism based on alterations in the defect structure of Cr 2O 3 is proposed to explain these dispersed oxide effects on isothermal oxidation behavior. It is based on a reduction in cation transport rates which in turn alter the rate of oxide growth. ThO 2-containing alloys fabricated by the mechanical alloying technique were found to have oxidation resistance fully equal to commercial TDNiCr. Com Ni-20Cr performed better than Lab Ni-20Cr, but not as well as TDNiCr. 相似文献
19.
Al 2O 3/TiCN-0.2% Y 2O 3 composites were fabricated by hot pressing sintering. The effect on mechanical property and microstructure of the sample composition and HP temperate was investigated. The results of Al 2O 3/TiCN-0.2% Y 2O 3 were satisfied. The bending strength, fracture toughness, Vickers hardness was respectively 1015 MPa, 6.89 MPa·m 1/2 20.82 MPa at 1650 °C for 20 min. Good wear resistance was found for the kind of ceramic material when used as cutting tools in the machining of the hardened carbon steel. By the compared experiment for the cutting performances, it could be seen that the performance of this composite material was better than that of the ceramic tool material YT15 for continuously cutting quenched steel. This kind of composite tool material is suitable for continuously cutting quenched steel No.45, especially intermittently cutting quenched steel. 相似文献
20.
In this work, α-SiC ceramics with aluminum or yttria sintering additives ranging from 1.0 to 4.0 wt pct were prepared by hot pressing, and the effect of sintering additives on the microstructure and mechanical properties of SiC ceramics was investigated. Specimens with Al additive exhibited fully dense microstructure with relative density > 99.4 pct. However, the relative density of specimens with Y2O3 decreases constantly from 99.5 to 95.7 pct as Y2O3 content increases, which is possibly due to the formation of gaseous phase and evaporation of volatile compounds resulting from the chemical reaction between SiC matrix and Y2O3 additive. X-ray diffraction (XRD) and Raman spectra results showed that Al addition leads to the transformation from 6H to 4H polytypes, and the transformation degree increases as increasing the Al content, while no obvious polytype transformation is observed for specimens with Y2O3 additive. Scanning electron microscopy (SEM) observations revealed that specimens with Y2O3 are composed of equiaxed grains with average size about 1.0 μm, whereas the specimens with Al additive exhibit larger grain size with partly elongated grain structure. Additionally, it is found that the grain growth of specimens with Al addition is accompanied by the polytype transformation. Further analysis revealed that, for specimens with Al additive, enhanced grain size and formation of elongated of SiC grains lead to an improvement in fracture toughness from 5.7 to 7.1 MPa m1/2 but a slight decline in flexural strength from 706 to 632 MPa. The crack deflection and bridging as well as undesirable stress effects related to the large elongated grains are responsible for the variation in mechanical properties. In the case of SiC sintered with Y2O3, there are obvious declines in flexural strength and fracture toughness from 714 to 492 MPa and from 5.9 to 3.4 MPa m1/2, respectively, which are mainly attributed to the increased porosity. The impact of Al and Y2O3 on the microstructure and mechanical properties of SiC ceramics was discussed. 相似文献
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