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1.
Crack-Tip Transformation Zones in Toughened Zirconia 总被引:1,自引:0,他引:1
David B. Marshall Michael C. Shaw Reinhold H. Dauskardt Robert O. Ritchie Michael J. Readey Arthur H. Heuer 《Journal of the American Ceramic Society》1990,73(9):2659-2666
Transformation zones surrounding cracks in several toughened magnesia-partially-stabilized zirconia ceramics are characterized by optical interference measurements of surface uplift and by Raman microprobe spectroscopy. The measurements demonstrate that the volume fraction of transformation is nonuniform within the zone and that the extent of the frontal zone is approximately the same as that of the wake. Results are used to evaluate the crack-tip shielding stress intensity factor and to compare with the measured fracture toughness. 相似文献
2.
David M. Stump 《Journal of the American Ceramic Society》1992,75(5):1264-1265
Previous results for ultimate tensile fracture strengths of partially stabilized zirconia (PSZ) containing preexisting finite cracks are reformulated in terms of a new transformation-strengthening parameter. This allows a simplified method for estimating the strengths of bulk PSZ containing arbitrarysized, preexisting critical cracks. 相似文献
3.
Mahyar S. Dadkhah David B. Marshall Winfred L. Morris Brian N. Cox 《Journal of the American Ceramic Society》1991,74(3):584-592
Residual strains responsible for crack tip shielding have been measured within transformation zones surrounding cracks in Mg-PSZ. Two techniques were used for strain measurement: moiré interferometry and high-resolution image matching. Both methods provide maps of differential in-plane displacements within the specimen surface intersected by the crack, the latter method with the higher resolution. The results are compared with finite-element analysis to assess surface relaxation effects, and the measured strains are used to evaluate the crack tip shielding stress intensity factor. Calculations based on the assumption that the unconstrained transformation strain is hydrostatic dilatation yielded results that were significantly smaller than the measured toughness increases. 相似文献
4.
Angela A. Steffen Reinhold H. Dauskardt Robert O. Ritchie 《Journal of the American Ceramic Society》1991,74(6):1259-1268
Cyclic fatigue stress/life ( S / N ) and crack-growth properties are investigated in magnesia-partially-stabilized zirconia (Mg-PSZ), with particular reference to the role of crack size. The material studied is subeutectoid aged to vary the steady-state fracture toughness, Kc , from ∼3 to 16 MPa · m1/2 · S / N data from unnotched specimens show markedly lower lives under tension—compression compared with tension—tension loading; "fatigue limits"(at 108 cycles) for the former case approach 50% of the tensile strength. Under tension—tension loading, cyclic crack-growth rates of "long"(> 3 mm) cracks are found to be power-law dependent on the stress-intensity range, Δ K , with a fatigue threshold, Δ K TH , of order 50% of Kc . Conversely, naturally occurring "small"(1 to 100 μm) surface cracks are observed to grow at Δ K levels 2 to 3 times smaller than Δ K TH , similar to behavior widely reported for metallic materials. The observed small-crack behavior is rationalized in terms of the restricted role of crack-tip shielding (in PSZ from transformation toughening) with cracks of limited wake, analogous to the reduced role of crack closure with small fatigue cracks in metals. The implications of such data for structural design with ceramics are briefly discussed. 相似文献
5.
J. Martinez-Fernandez M. Jimenez-Melendo A. Dominguez-Rodriguez Arthur H. Heuer 《Journal of the American Ceramic Society》1991,74(5):1071-1081
The temperature dependence of the Vickers microhardness was studied in 3.4-mol%-Y2 O3 -partially-stabilized ZrO2 (Y-PSZ) single crystals up to 1000°C; the samples had previously been annealed at 1600°C for 150 h to develop "colony" precipitates of tetragonal ZrO2 in the cubic ZrO2 matrix. Indentation caused extensive stress-induced martensitic transformation of the colony precipitates to monoclinic symmetry in zones which extended in extreme cases up to several hundred micrometers from the indent. For indents made at 500°C and above, the M d and M f temperatures are 450° and 310°C, respectively; A s is ∼600°C ( M d is the temperature of initial transformation (the "martensite start temperature") in deformed samples; M f is the temperature at which the final transformation occurs; A s is the temperature at which the reverse (monoclinic → tetragonal) transformation begins). However, extensive transformation zones are also found for indents made at 200°, 300°, and 400°C. The dislocation density introduced during indentation is responsible for nucleating the transformation in a zone adjacent to the indent. However, the transformation zone extends further than the plastic zone around the indent, indicating extensive autocatalytic transformation. Transformation within the zone appeared to occur in individual plates with {110} habit planes. The plate dimensions (∼100 μm ×∼175 μm ×∼10 μm) are large compared to the size of the colony precipitates (∼2 μm in maximum dimension). 相似文献
6.
Phase Transformation in EB-PVD Yttria Partially Stabilized Zirconia Thermal Barrier Coatings during Annealing 总被引:1,自引:0,他引:1
Uwe Schulz 《Journal of the American Ceramic Society》2000,83(4):904-910
Electron-beam physical-vapor-deposited thermal barrier coatings consisting of ZrO2 stabilized by 7 wt% Y2 O3 were investigated in regard to phase transformation after annealing. Free-standing ceramic layers were heat-treated in air, for up to 200 h, in the temperature range 1200°—1400°C and then analyzed by X-ray diffractometry. Based on information obtained from the {111} and {400} peaks, the phase composition and the Y2 O3 content in the phases were calculated. At the start of transformation, small grains of a low-Y2 O3 t phase and a c phase formed. After >30 h at 1300°C and at 1400°C, a mixture of a t phase deficient in Y2 O3 , an m phase, and a c phase formed after cooling, with the Y2 O3 contents in the phases roughly predicted by the phase diagrams. The results of the present study are discussed here in detail and compared with data for plasma-sprayed coatings. 相似文献
7.
Christopher J. Howard Erich H. Kisi Ronald B. Roberts Roderick J. Hill 《Journal of the American Ceramic Society》1990,73(10):2828-2833
Neutron powder diffraction and conventional dilatometry have been used to investigate the tetragonal-to-orthorhombic phase transformation and the orthorhombic-to-tetragonal reversion in a high-toughness magnesia-partially-stabilized zirconia. For this material, the onset temperature on cooling for the tetragonal-to-orthorhombic transformation (determined by dilatometry) was 192 K, and the reversion on subsequent heating occurred between 500 and 620 K. Neutron diffraction patterns were recorded at temperatures down to 19 K then up to 664 K, and analyzed by the multiphase Rietveld method to determine the amounts of different phases as well as their lattice parameters and unit-cell volumes. It is notable that, at its maximum, the orthorhombic phase amounted to 45% of the sample by weight. Length changes were measured, using pushrod dilatometers, in the temperature range 80 to 700 K. Length changes calculated from the neutron diffraction determinations of the proportions and unit-cell volumes of the different phases are in very good agreement with the directly measured values. 相似文献
8.
Jeong-Joo Kim Chan Park Doh-Yeon Kim Duk N. Yoon Alexander Shapiro 《Journal of the American Ceramic Society》1990,73(12):3658-3662
When partially stabilized zirconia with 6 mol% MgO and 4 mol% CaO is aged at 1450°C, intragranular precipitation occurs and concurrently the boundaries between the grains migrate, forming a Ca-enriched precipitate-free cubic phase and large tetragonal precipitates behind them. At these compositions and temperature the boundary migration is rapid and shows the characteristics of a discontinuous coarsening. A uniaxial compressive stress applied to this specimen during the aging treatment increases or decreases the migration rate of the boundaries parallel or perpendicular to the stress axis, respectively, in agreement with the prediction that a compressive coherency strain due to the diffusion of Ca atoms is produced at the surface of the retreating grains and drives the migration. The diffusional coherency strain energy is thus expected to be the dominant driving force for the discontinuous coarsening in this solid. 相似文献
9.
Anisotropic elastic response of microcracked bodies has been studied using transformation-toughened Mg-PSZ and Ce-TZP as model materials. These zirconias have been previously deformed in triaxial compression to effect various extents of phase transformation. Microcracks were found to align with the compression axis and their normalized density increases linearly with the extent of transformation plasticity. The measured elastic constants are anisotropic and well described by an elasticity theory. An additional anomalous elastic anisotropy was also found in Ce-TZP due to a transformation texture of both the remaining tetragonal phase and the newly formed monoclinic phase. The terminal crack density ω= Na 3 , where N is the number of cracks per unit volume and a is the crack radius, reaches 0.05 in Mg-PSZ and 0.1 in Ce-TZP at the completion of transformation plasticity. 相似文献
10.
Christopher J. Howard Erich H. Kisi Osamu Ohtaka 《Journal of the American Ceramic Society》1991,74(9):2321-2323
The crystal structures of orthorhombic zirconias formed by cooling magnesia-partially-stabilized zirconia (Mg-PSZ) (space group Pbc 21 ) and by quenching zirconia powder from 600°C and 6 GPa (space group Pbca ) are compared and contrasted. It is demonstrated that the two structures are easily distinguished by the neutron powder diffraction techniques used to establish them. The occurrence of two distinct phases is hence proved. Structural relationships between these two phases and also with the in situ high-pressure structure proposed from X-ray diffraction (XRD) are discussed. The three structures are virtually indistinguishable by XRD and so the structure of the high-pressure form "in situ" is considered to remain unknown. 相似文献
11.
Charles S. Montross 《Journal of the American Ceramic Society》1992,75(2):463-468
Magnesia-partially-stabilized zirconia (Mg-PSZ) is industrially important because of transformable metastable tetragonal precipitates which interact with and arrest cracks. This work addresses the precipitation of tetragonal phases at one composition, 9.5 mol% MgO, throughout a range of temperatures. High-purity zirconia samples were sintered at 1700°C and rapidly quenched to heat-treatment temperatures ranging from 1600° to 1100°C, then quenched to room temperature. Cooling rates through the tetragonal + MgO and the monoclinic + MgO two-phase regions were found to affect the phase content. The kinetics of nonequilibrium phase transformation for high-purity Mg-PSZ are presented in terms of time-temperature-transformation diagrams. 相似文献
12.
Transformation plasticity in magnesia-partially-stabilized zirconia (Mg-PSZ) is studied using a split Hopkinson pressure bar modified for ceramic materials. Axial and transverse strains are measured under uniaxial compressive loading at a strain rate of 250/s. The transformation yield stress is found to increase from 900 MPa under quasi-static loading to 1.2 GPa at high strain rate. Post-yield deformation is characterized by shear and volumetric plastic strains up to 1.2%. During unloading, the axial and transverse plastic strains are partially recovered while the volume is conserved. Axially oriented microcracks are observed but they do no contribute significantly to plastic deformation in Mg-PSZ. 相似文献
13.
化学共沉淀法制备微晶PSZ陶瓷的显微结构与力学性能 总被引:9,自引:0,他引:9
采用化学共沉淀法制备ZrO2-MgO-Y2O3系和ZrO2-MgO-Y2O3系均匀超细活性粉末,经化学组成和显微结构设计,获得了固溶湿度小于等于1550℃且致密烧结的微晶PSZ复相陶瓷,其常温抗弯强度为766MPa,断裂韧性K1c为12.5MPa·m^1/2。研究了MgO和Al2O3以及1100℃热处理时间对材料显微结构、相组成和力学性能的影响。 相似文献
14.
Charles A. Bateman Michael R. Notis David B. Williams 《Journal of the American Ceramic Society》1989,72(12):2372-2376
The coarsening kinetics of the tetragonal phase in a magnesia-partiallystabilized zirconia at 1420°C was examined using transmission electron microscopy and found to be controlled by volume diffusion. The rate constant was larger and the particle-size distribution was broader than predicted by the Lifshitz–Slyozov–Wagner theory of particle coarsening. A volume fraction modified coarsenng theory was found which better fits the experimental rate constant and particle-size distribution. 相似文献
15.
Rachman Chaim 《Journal of the American Ceramic Society》1992,75(3):694-699
Microstructure and bending strength of commercial (MgO,CaO)-partially-stabilized zirconia subjected to heat treatments in the temperature range 900° to 1550°C were characterized. The as-received optimally aged material contained small ellipsoid-shaped tetragonal ( t ) precipitates dispersed homogeneously in the cubic ( c ) grains. Annealing at lower temperatures caused isothermal martensitic transformation to the monoclinic ( m ) phase. Annealing at higher temperatures caused formation of chevronlike and irregularshaped cluster precipitates, due to stress-induced coarsening and precipitate impingement. The loss of bending strength was related to the stored strain energy contributed by each type of precipitate morphology, in addition to decrease in the volume fraction of the t phase. 相似文献
16.
Erich H. Kisi Christopher J. Howard Roderick J. Hill† 《Journal of the American Ceramic Society》1989,72(9):1757-1760
A neutron powder diffraction investigation confirms that, in tough magnesiapartially-stabilized zirconia cooled to 30 K, most of the tetragonal zirconia transforms to an orthorhombic phase. This phase is retained on heating to room temperature; the lattice parameters at 295 K are a = 0.5068, b = 0.5260, and c = 0.5077 nm. The room-temperature crystal structure (space group Pbc21 ) is determined by multiphase Rietveld refinement from the neutron diffraction pattern. This orthorhombic structure is compared with the parent tetragonal structure and with the structure of monoclinic zirconia, which it closely resembles. 相似文献
17.
Samples of 3 mol% Y2 O3 -stabilized tetragonal ZrO2 ceramics were annealed at 250°C in atmospheres of water vapor pressures of 1 bar and 26 mbar. As demonstrated by the water uptake and the lattice expansion, water molecules were incorporated into the ZrO2 lattice during annealing, and the amount of the incorporated water is determined by the water vapor pressure. Owing to the filling of oxygen vacancies by the incorporated water molecules, part of the tetragonal ZrO2 transformed to the monoclinic structure, and protonic defects were induced. The expected proton conduction was confirmed by the polarity of the water vapor concentration cells. 相似文献
18.
Ram Srinivasan Burtron H. Davis O. Burl Cavin Camden R. Hubbard 《Journal of the American Ceramic Society》1992,75(5):1217-1222
Amorphous zirconia precursors were made by the precipitation of a zirconium tetrachloride solution with either slow (8 h) or rapid additions of ammonium hydroxide at a pH of 10.5. Following calcination at 500°C for 4 h, the rapidly precipitated precursor exhibited predominantly monoclinic ZrO2 phase, while the slowly precipitated precursor produced the tetragonal ZrO2 phase. The crystallization and phase transformations were followed by in situ high-temperature X-ray diffraction (HTXRD) for both specimens in helium and in air. Each amorphous precursor first crystallizes as the tetragonal phase at about 450°C. A tetragonal-to-monoclinic phase transformation of the rapidly precipitated material was observed on cooling at about 275°C. Surface impregnation of sulfate ions following precipitation inhibited the tetragonal-to-monoclinic transformation for the rapidly precipitated ZrO2 sample. The crystallite size for the t -ZrO2 of all samples, irrespective of whether they transform to monoclinic, was approximately 11 nm, indicating that the t → m transformation in these materials is not controlled by differences in crystallite size. It is therefore suggested that anionic vacancies control the tetragonal-to-monoclinic phase transformation on cooling, and that oxygen adsorption triggers this phase transformation. 相似文献
19.
研究了添加Y2O3对MgPSZ显微结构及力学性能的影响。结果表明,MgPSZ中引入Y2O3有利于降低烧结温度,促进立方化完全,但烧结体的力学性能有所降低。在1400℃下热处理,(Mg,Y)PSZ材料与MgPSZ一样发生cZrO2→tZrO2的析出过程,析出纺锤状四方ZrO2晶体。1400℃热处理10h获得最大抗弯强度达648MPa,断裂韧性K1c为8.3MPa·m1/2。Y2O3的加入使获得优异力学性能的热处理范围变宽,因而工艺上容易控制。但Y2O3加入过多使析出困难。最佳加入量为1.0%(摩尔百分数)。Y2O3的加入还使材料的Weibul模数增高至18.46,表明(Mg,Y)PSZ经热处理后能消除内部缺陷,使材料可靠性提高。 相似文献
20.
Grinding Temperature Measurements in Magnesia-Partially-Stabilized Zirconia Using Infrared Spectrometry 总被引:1,自引:0,他引:1
Adam C. Curry Albert J. Shih Jin Kong Ronald O. Scattergood Sam B. McSpadden 《Journal of the American Ceramic Society》2003,86(2):333-341
Results of temperature measurements by analysis of the thermal emission spectra generated during grinding and subsequently transmitted through partially stabilized zirconia workpieces are presented. Portions of emitted visible and near-infrared spectra were collected with spectrometers. Source temperatures were determined by fitting the scaled spectrometer output spectra to blackbody curves. Simulations showed that the effective temperatures determined by this method will be strongly biased toward hot-spot (flash) temperatures, which are expected to occur at the grinding grit–workpiece interface. Hot-spot temperatures on the order of 3000 K were obtained for grinding with both SiC and diamond wheels. These high temperatures modify the grinding process and the phase content of grinding chips. 相似文献