Zirconia ceramics have become increasingly widely used in recent years and are favored by relevant enterprises. From the traditional dental field to aerospace, parts manufacturing has been used, but there is limited r...Zirconia ceramics have become increasingly widely used in recent years and are favored by relevant enterprises. From the traditional dental field to aerospace, parts manufacturing has been used, but there is limited research on the deformation and damage process of zirconia ceramics. This article analyzes the acoustic emission characteristics of each stage of ceramic damage from the perspective of acoustic emission, and explores its deformation process characteristics from multiple perspectives such as time domain, frequency, and EWT modal analysis. It is concluded that zirconia ceramics exhibit higher brittleness and acoustic emission strength than alumina ceramics, and when approaching the fracture, it tends to generate lower frequency acoustic emission signals.展开更多
The sintering behavior and mechanical properties of zirconia doped with 2.0mol%-3.0mol%Y_(2)O_(3)were studied by pressure-less sintering.The experimental results show that the densification temperature of zirconia cer...The sintering behavior and mechanical properties of zirconia doped with 2.0mol%-3.0mol%Y_(2)O_(3)were studied by pressure-less sintering.The experimental results show that the densification temperature of zirconia ceramics increases gradually with the decrease of Y_(2)O_(3)doping content by which decreases the sintering driving force due to the lower oxygen vacancy concentration of the systems.Furthermore,the bending strength and fracture toughness of the prepared zirconia ceramics increase with the decrease of Y_(2)O_(3)doping content.It can be attributed to the fact that the phase stability of tetragonal zirconia decreases with the decrease of Y_(2)O_(3)doping content,which is easier to induce"phase transformation toughening"and dissipate impact energy.The relative density,bending strength and fracture toughness of 2.0 mol%Y_(2)O_(3)doped zirconia ceramics(2.0Y-ZrO_(2))sintered at 1525℃are 99.00%,1256.65±20.82 MPa and 9.85±0.13 MPa·m^(1/2),respectively.展开更多
Despite its unique high efficiency and good environmental compatibility, the water-soluble binder system still encounters problems achieving a desired sintered part via ceramic injection molding because of the poor co...Despite its unique high efficiency and good environmental compatibility, the water-soluble binder system still encounters problems achieving a desired sintered part via ceramic injection molding because of the poor compatibility and the powder-binder segregation between ceramic powders and binders. The objective of this study was to obtain a sintered part with excellent properties by introducing a small quantity of oleic acid to the surface of zirconia powders before the mixing process. As opposed to many previous investigations that focused only on the rheological behavior and modification mechanism, the sintering behavior and densification process were systematically investigated in this study. With the modified powders, debound parts with a more homogeneous and smaller pore size distribution were fabricated. Also, a higher density and greater flexural strength were achieved in the sintered parts fabricated using the modified powders.展开更多
Tetragonal ZrO2-3 mol% Y2O3 (3Y-TZP) coated with CePO4 was synthesized by a co-precipitation method and the effects of CePO4 content and sintering temperature on its mechanical properties were investigated. The micr...Tetragonal ZrO2-3 mol% Y2O3 (3Y-TZP) coated with CePO4 was synthesized by a co-precipitation method and the effects of CePO4 content and sintering temperature on its mechanical properties were investigated. The microstructure and phase composition of the products were characterized using scanning and transmission electron microscopy as well as X-ray diffraction, respectively. The machinability index of CePO4-coated zirconia was calculated to be 1.05 when the CePO4 content is 25 wt.%. The sample hardness, bending strength and fracture toughness are 7.08 GPa, 457.85 MPa and 9.75 MPa m1/2, respectively, when the sintering temperature is 1400°C. The results show that as-prepared CePO4-coated 3Y-TZP ceramics are highly suitable biomaterials for dental applications and are expected to be used in a com-puter-aided design and computer-aided manufacturing (CAD/CAM) system to make dental crowns or bridge prostheses in a one-step sinter-ing process.展开更多
Y2O3-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics with high-performance were prepared for dental ap- plication by use of the micro-emulsion and two-step sintering method. The crystal phase, morpho...Y2O3-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics with high-performance were prepared for dental ap- plication by use of the micro-emulsion and two-step sintering method. The crystal phase, morphology, and microstructure of the reaction products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron mi- croscopy (TEM). XRD results show that the ceramics mainly consist of tetragonal zirconia. Physical and mechanical properties test results show that the bending strength, fracture toughness, and the density of full sintered Y-TZP ceramics are 1150 MPa, 5.53 MPa.m1/2, and 6.08 g/cm3, respectively, which suggest that the material is relatively suitable for dental restoration. The dental base crown machined with this material by CAD/CAM system exhibits a verisimilitude configuration and the material's expansion coefficient well matches that of the glaze. These results further indicate that the product can be used as a promising new ceramic material to fabricate dental base crowns and bridges.展开更多
Owing to their low density and attractive high-temperature properties, gamma titanium aluminide alloys (TiAl alloys, hereafter) have significant potential application in the aerospace and automobile industries, in whi...Owing to their low density and attractive high-temperature properties, gamma titanium aluminide alloys (TiAl alloys, hereafter) have significant potential application in the aerospace and automobile industries, in which these materials may replace the heavier nickel-based superalloys at service temperatures of 600-900℃. Investment casting of TiAl alloys has become the most promising cost-effective technique for the manufacturing of TiAl components. Ceramic moulds are fundamental to fabricating the TiAl casting components. In the present work, ceramic mould with a zirconia primary coat was designed and fabricated successfully. Investment casting of TiAl blades and tensile test of specimens was carried out to verify the correctness and feasibility of the proposed method. The tensile test results indicate that, at room temperature, the tensile strength and the elongation are about 450 MPa and 0.8%, respectively. At 700℃, the tensile strength decreases to about 410 MPa and the elongation increases to 2.7%. Microstructure and mechanical properties of investment cast TiAl alloy are discussed.展开更多
Objective:To evaluate the shear bond strength(SBS) between alumina-toughened zirconia (ATZ) cores and veneering ceramics,investigate the effect of aging in artificial saliva on SBS and compare it with that of yttria-s...Objective:To evaluate the shear bond strength(SBS) between alumina-toughened zirconia (ATZ) cores and veneering ceramics,investigate the effect of aging in artificial saliva on SBS and compare it with that of yttria-stabilized tetragonal zirconia polycrystals(Y-TZP).Methods:Bars of ATZ and Y-TZP were layered with veneering ceramics in accordance to the recommendation of the manufacturer.Half of each group(n = 10) was aged at 134℃.(under 2 bar pressure) in an autoclave for 48 h.Subsequently,all specimens were subjected to shear force in a universal testing machine.The interface and fractured surface of the specimens were evaluated using scanning electron microscopy and X-ray energy dispersive spectroscopy.Results:The initial mean SBS values in MPa±SD were 28.9±8.0 for ATZ and 26.2±7.6 for Y-TZP.After aging,the mean SBS values for ATZ and Y-TZP were 22.9±4.9 MPa and 22.8±6.9 MPa,respectively.Neither the differences between the SBS values of the ATZ and Y-TZP groups nor the influence of aging on all groups were statistically significant.Conclusions:The SBS between the ATZ core and the veneering ceramics was not affected by aging.The SBS of ATZ to veneering ceramics was not significantly different compared with that of Y-TZP.展开更多
The influence of various alumina additions on the optical property of zirconia/alumina composite ceramics was investigated. The relative sintered densities, transmittances, color and the microstructure of the composit...The influence of various alumina additions on the optical property of zirconia/alumina composite ceramics was investigated. The relative sintered densities, transmittances, color and the microstructure of the composite ceramics were studied. The experimental results showed that the relative sintered densities and transmittances decreased with alumina addition. The lightness increased obviously but the chroma change was small. Pure zirconia nanopowders sintered densely could obtain the relatively high transmittance, while the transmittance and the lightness of slight addition changed significantly. The zirconia/alumina composite ceramics with alumina addition less than 7.5wt% could achieve the relatively stable and reliable optical properties.展开更多
The possibility to produce advanced alumina and zirconia ceramics by the electroconsolidation method is studied. The technological parameters of Al2O3 and ZrO2 (3 mass% Y2O3 ) production were developed and optimized...The possibility to produce advanced alumina and zirconia ceramics by the electroconsolidation method is studied. The technological parameters of Al2O3 and ZrO2 (3 mass% Y2O3 ) production were developed and optimized. Electroconsolidated alumina and zirconia ceramics have higher values of properties in comparison with ordinary sintered samples in air. Advanced proper- ties of electroconsolidated ceramics are defined by homo- geneous, ultradense and fine-crystalline structure that was formed due to the effect to consolidate the materials to high density for a shortest time.展开更多
The zirconia ceramic ring was prepared using fused monoclinic zirconia as main starting material, adopting composite stabilizer of magnesia, yttria and calcium nitrate, and applying recombination technology of traditi...The zirconia ceramic ring was prepared using fused monoclinic zirconia as main starting material, adopting composite stabilizer of magnesia, yttria and calcium nitrate, and applying recombination technology of traditional refractories and ceramics. Effect of the preparation process on material properties was comparatively studied, and the microstructure and phase composition were analyzed. The results show that adopting the high-speed mixing granulation process and the appropriate heat treatment can realize the control on the phase composition and microstructure, the zirconia ceramic ring with good thermal shock resitance and mechanical properties can be prepared.展开更多
Wear resistance of several zirconia toughened ceramics in comparison with a metal-ceramic Co-WC has been studied in drawing wire field test. Result indicates that the harder the ceramic die, the longer the service lif...Wear resistance of several zirconia toughened ceramics in comparison with a metal-ceramic Co-WC has been studied in drawing wire field test. Result indicates that the harder the ceramic die, the longer the service life. Excellent wear resistance of ceramic die is obtained with a very high hardness (19 GPa). The service life is nearly three times that of Co-WC die. SEM observation on wear surfaces showed that material removal is mainly caused by plastic flow and ploughing process. But when the ceramic is composed of zirconia, alumina and some titanium carbide, micro-chipping and tribochemical reaction take place, and wear rate increases. Wear and friction induced martensite was detected by XRD. The T-M (tetragonal to monoclinic) phase transformation has a contribution to inhibiting microfracture.展开更多
The performances of fine-crystalline zirconia ceramics in workpiece ultrasonic vibration grinding (WUVG) and conventional grinding (CG) with diamond wheel were researched. The effects of WUVG and CG on material remova...The performances of fine-crystalline zirconia ceramics in workpiece ultrasonic vibration grinding (WUVG) and conventional grinding (CG) with diamond wheel were researched. The effects of WUVG and CG on material removal rate, grinding forces, surface roughness and microstructure of zirconia ceramic were investigated. Experimental results indicated that: (1) The material removal rate (MRR) in ultrasonic grinding process is two times as large as that of in conventional grinding. The material removal rate increases with increasing grinding depth in both ultrasonic grinding and conventional grinding. (2) The ultrasonic vibration grinding force is lower than that of conventional grinding force, and the increase of the worktable speed leads to a decrease of the grinding force, while the grinding force increases with larger grinding depth in both WUVG and CG. (3) The surface of ultrasonic vibration grinding has no spur and build-up edge and its surface roughness is smaller than that of CG significantly. Surface quality of WUVG is superior to that of conventional grinding, it is easy for ultrasonic vibration grinding that material removal mechanism is ductile grinding.展开更多
Polycrystalline 3Y-TZP/Al2O3 tetragonal zirconia fiber was obtained by the pyrolysis of gel fibers using zirconium oxychloride octahydrate(ZOC) as the raw material. The spinnable zirconia sol was prepared by electro...Polycrystalline 3Y-TZP/Al2O3 tetragonal zirconia fiber was obtained by the pyrolysis of gel fibers using zirconium oxychloride octahydrate(ZOC) as the raw material. The spinnable zirconia sol was prepared by electrolyzing the zirco-nium oxychloride octahydrate(ZOC) solution in the presence of acetic acid and sugar( sucrose, glucrose or fructose) , in which the molar ratios of CH3 COOH/ZOC and sugar/ZOC were 1.0-4.0 and 0.2-0.4, respectively. The pre- pared tetragonal zireonia fibers sintered at different temperatures showed smooth and crack-free surfaces with diame, ters of 5-10 μm. The addition of Al2O3 enhanced the sintering process and prevented the crystals from growing. Thermogravimetric analysis(TG), X-ray diffraction ( XRD ), Fourier transform infrared spectroscopy(FTIR), and scanning electron microscope(SEM) techniques were used to characterize the prepared fibers.展开更多
The aim of this work was to investigate the microstructure and mechanical properties of 1vol%-Ni-added yttria-stabilized zirconia (YSZ) toughened alumina composites. First, Ni powders were heterogeneously precipitated...The aim of this work was to investigate the microstructure and mechanical properties of 1vol%-Ni-added yttria-stabilized zirconia (YSZ) toughened alumina composites. First, Ni powders were heterogeneously precipitated in an alumina–zirconia powder mixture suspended in water;the prepared specimens were then pressureless sintered at 1550°C/2 h in a 90vol%Ar/10vol% H2 atmosphere. The structure of phases and microstructure of the composites were characterized by X-ray diffraction and scanning electron microscopy, respectively. Mechanical characterization of the specimens was carried out through Vickers hardness, Vickers indentation toughness, and three-point flexural bending tests. The fine Ni particles were homogeneously dispersed throughout the alumina matrix because of the employed processing method. Furthermore, hardness and toughness values were found to increase by 8% and 50%, respectively, with Ni addition, whereas the relative densities and flexural strength values were found to remain unchanged.展开更多
The ZrO2-Al2O3 ceramic composites were prepared by appropriate techniques with commercial ZrO2 and Al2O3 powders as raw materials and Y2O3 as stabilizer. The results indicate that with the introduction of Al2O3 into t...The ZrO2-Al2O3 ceramic composites were prepared by appropriate techniques with commercial ZrO2 and Al2O3 powders as raw materials and Y2O3 as stabilizer. The results indicate that with the introduction of Al2O3 into the ZrO2 matrix where the quantity of additive Y2O3 is 3.5% (mole fraction), the growth of ZrO2 grains is efficiently inhibited, which helps the ZrO2 grains exist in a metastable tetragonal manner; thus higher strength and toughness are acquired. When the content of alumina is 20% (mass fraction), the bending strength and fracture toughness of the composites are 676.7 MPa and 10 MPa·m1/2 respectively, the mechanical behaviors are close to those prepared with ZrO2 and Al2O3 powders synthesized through wet chemical approach. The mechanical behaviors of the composites are well improved owing to the dispersion toughening of alumina grains and phase transformation toughening of zirconia grains.展开更多
ntergranular slow crack growth in zirconia polycrystal is described with a cohesive zone model that simulate mechanically the reaction-rupture mechanism underlying stress and environ- mentally assisted failure. A 2D p...ntergranular slow crack growth in zirconia polycrystal is described with a cohesive zone model that simulate mechanically the reaction-rupture mechanism underlying stress and environ- mentally assisted failure. A 2D polycrystal is considered with cohesive surfaces inserted along the grain boundaries. The anisotropic elastic modulus and grain-to-grain misorientation are accounted for together with an initial stress state related to the processing. A minimum load threshold is shown to originate from the onset of the reaction-rupture mechanism to proceed where a minimum traction is reached locally and from the magnitude of the initial compression stresses. This work aims at providing reliable predictions in long lasting applications of ceramics.展开更多
The present investigation demonstrated the comparative studies carried out on conventional, microwave and vacuum sintering of alumina added yttria stabilized zirconia (YSZ). The conventional, microwave and vacuum sint...The present investigation demonstrated the comparative studies carried out on conventional, microwave and vacuum sintering of alumina added yttria stabilized zirconia (YSZ). The conventional, microwave and vacuum sintered specimens were characterized by density measurement, XRD, SEM with EDX analysis and hardness evaluation. Microwave sintering was proved to be the best efficient sintering technique with respect to energy and time savings. Enhanced densification was observed for the microwave and vacuum sintered specimens at lower temperatures compared to the conventionally sintered ones. Further, it was observed that the particle size had significant influence on the enhancement of densification. The microwave sintered specimen showed the highest hardness compared to conventional and vacuum sintered specimens.展开更多
A novel method based on polyacrylamide gel process was used to prepare Li2O-Al2O3-SiO2 (LAS) glass-ceramic powders. The effects of ZrO2 addition on the crystallization and phase transformation process in LAS system ...A novel method based on polyacrylamide gel process was used to prepare Li2O-Al2O3-SiO2 (LAS) glass-ceramic powders. The effects of ZrO2 addition on the crystallization and phase transformation process in LAS system were investigated by using differential thermal analysis (DTA), X-ray powder diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR). The activation energy decreases from 304.6 to 248.9kJ/mol and the frequency factor decreases from 2.49×10 11 to 5.56×108 min -1 as ZrO2 content changes from 0 to 4.0%(mass fraction). During calcination from 800 to 1200℃, hexagonal β-quartz solid-solution first crystallizes and then gradually transforms into tetragonal β-spodumene solid-solution with increasing temperature. The stability of β-quartz solid-solution increases with more ZrO2 additions and a minor crystalline phase, tetragonal zirconia, also appears.展开更多
文摘Zirconia ceramics have become increasingly widely used in recent years and are favored by relevant enterprises. From the traditional dental field to aerospace, parts manufacturing has been used, but there is limited research on the deformation and damage process of zirconia ceramics. This article analyzes the acoustic emission characteristics of each stage of ceramic damage from the perspective of acoustic emission, and explores its deformation process characteristics from multiple perspectives such as time domain, frequency, and EWT modal analysis. It is concluded that zirconia ceramics exhibit higher brittleness and acoustic emission strength than alumina ceramics, and when approaching the fracture, it tends to generate lower frequency acoustic emission signals.
基金Funded by the National Key Research and Development Plan of China(No.2021YFB3701401)the National Natural Science Foundation of China(Nos.92163208,51902233,51972243,51521001,and 51832003)。
文摘The sintering behavior and mechanical properties of zirconia doped with 2.0mol%-3.0mol%Y_(2)O_(3)were studied by pressure-less sintering.The experimental results show that the densification temperature of zirconia ceramics increases gradually with the decrease of Y_(2)O_(3)doping content by which decreases the sintering driving force due to the lower oxygen vacancy concentration of the systems.Furthermore,the bending strength and fracture toughness of the prepared zirconia ceramics increase with the decrease of Y_(2)O_(3)doping content.It can be attributed to the fact that the phase stability of tetragonal zirconia decreases with the decrease of Y_(2)O_(3)doping content,which is easier to induce"phase transformation toughening"and dissipate impact energy.The relative density,bending strength and fracture toughness of 2.0 mol%Y_(2)O_(3)doped zirconia ceramics(2.0Y-ZrO_(2))sintered at 1525℃are 99.00%,1256.65±20.82 MPa and 9.85±0.13 MPa·m^(1/2),respectively.
基金financially supported by the National Natural Science Foundation of China (Nos. 51572035 and 51502041)
文摘Despite its unique high efficiency and good environmental compatibility, the water-soluble binder system still encounters problems achieving a desired sintered part via ceramic injection molding because of the poor compatibility and the powder-binder segregation between ceramic powders and binders. The objective of this study was to obtain a sintered part with excellent properties by introducing a small quantity of oleic acid to the surface of zirconia powders before the mixing process. As opposed to many previous investigations that focused only on the rheological behavior and modification mechanism, the sintering behavior and densification process were systematically investigated in this study. With the modified powders, debound parts with a more homogeneous and smaller pore size distribution were fabricated. Also, a higher density and greater flexural strength were achieved in the sintered parts fabricated using the modified powders.
基金supported by the National High-Technology Research and Development Program of China (No.2009AA03Z422)
文摘Tetragonal ZrO2-3 mol% Y2O3 (3Y-TZP) coated with CePO4 was synthesized by a co-precipitation method and the effects of CePO4 content and sintering temperature on its mechanical properties were investigated. The microstructure and phase composition of the products were characterized using scanning and transmission electron microscopy as well as X-ray diffraction, respectively. The machinability index of CePO4-coated zirconia was calculated to be 1.05 when the CePO4 content is 25 wt.%. The sample hardness, bending strength and fracture toughness are 7.08 GPa, 457.85 MPa and 9.75 MPa m1/2, respectively, when the sintering temperature is 1400°C. The results show that as-prepared CePO4-coated 3Y-TZP ceramics are highly suitable biomaterials for dental applications and are expected to be used in a com-puter-aided design and computer-aided manufacturing (CAD/CAM) system to make dental crowns or bridge prostheses in a one-step sinter-ing process.
文摘Y2O3-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics with high-performance were prepared for dental ap- plication by use of the micro-emulsion and two-step sintering method. The crystal phase, morphology, and microstructure of the reaction products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron mi- croscopy (TEM). XRD results show that the ceramics mainly consist of tetragonal zirconia. Physical and mechanical properties test results show that the bending strength, fracture toughness, and the density of full sintered Y-TZP ceramics are 1150 MPa, 5.53 MPa.m1/2, and 6.08 g/cm3, respectively, which suggest that the material is relatively suitable for dental restoration. The dental base crown machined with this material by CAD/CAM system exhibits a verisimilitude configuration and the material's expansion coefficient well matches that of the glaze. These results further indicate that the product can be used as a promising new ceramic material to fabricate dental base crowns and bridges.
基金supported by the National Basic Research Program of China (973 Program) under contract No.2011CB 605502the National Natural Science Foundation of China under Grant No. 51001040+1 种基金the Specialized Research Fund for the Doctoral Program of Higher Education within the project No.200802130014the Development Program for Outstanding Young Teachers in Harbin Institute of Technology (HITQNJS 2009022)
文摘Owing to their low density and attractive high-temperature properties, gamma titanium aluminide alloys (TiAl alloys, hereafter) have significant potential application in the aerospace and automobile industries, in which these materials may replace the heavier nickel-based superalloys at service temperatures of 600-900℃. Investment casting of TiAl alloys has become the most promising cost-effective technique for the manufacturing of TiAl components. Ceramic moulds are fundamental to fabricating the TiAl casting components. In the present work, ceramic mould with a zirconia primary coat was designed and fabricated successfully. Investment casting of TiAl blades and tensile test of specimens was carried out to verify the correctness and feasibility of the proposed method. The tensile test results indicate that, at room temperature, the tensile strength and the elongation are about 450 MPa and 0.8%, respectively. At 700℃, the tensile strength decreases to about 410 MPa and the elongation increases to 2.7%. Microstructure and mechanical properties of investment cast TiAl alloy are discussed.
基金supported by National High-Tech Research and Development Program of China(863 Program)(No.2006AA03Z440)
文摘Objective:To evaluate the shear bond strength(SBS) between alumina-toughened zirconia (ATZ) cores and veneering ceramics,investigate the effect of aging in artificial saliva on SBS and compare it with that of yttria-stabilized tetragonal zirconia polycrystals(Y-TZP).Methods:Bars of ATZ and Y-TZP were layered with veneering ceramics in accordance to the recommendation of the manufacturer.Half of each group(n = 10) was aged at 134℃.(under 2 bar pressure) in an autoclave for 48 h.Subsequently,all specimens were subjected to shear force in a universal testing machine.The interface and fractured surface of the specimens were evaluated using scanning electron microscopy and X-ray energy dispersive spectroscopy.Results:The initial mean SBS values in MPa±SD were 28.9±8.0 for ATZ and 26.2±7.6 for Y-TZP.After aging,the mean SBS values for ATZ and Y-TZP were 22.9±4.9 MPa and 22.8±6.9 MPa,respectively.Neither the differences between the SBS values of the ATZ and Y-TZP groups nor the influence of aging on all groups were statistically significant.Conclusions:The SBS between the ATZ core and the veneering ceramics was not affected by aging.The SBS of ATZ to veneering ceramics was not significantly different compared with that of Y-TZP.
基金Funded by the National High-Tech Research and Development Program of China (863 Program) (No. 2006AA03Z440)
文摘The influence of various alumina additions on the optical property of zirconia/alumina composite ceramics was investigated. The relative sintered densities, transmittances, color and the microstructure of the composite ceramics were studied. The experimental results showed that the relative sintered densities and transmittances decreased with alumina addition. The lightness increased obviously but the chroma change was small. Pure zirconia nanopowders sintered densely could obtain the relatively high transmittance, while the transmittance and the lightness of slight addition changed significantly. The zirconia/alumina composite ceramics with alumina addition less than 7.5wt% could achieve the relatively stable and reliable optical properties.
文摘The possibility to produce advanced alumina and zirconia ceramics by the electroconsolidation method is studied. The technological parameters of Al2O3 and ZrO2 (3 mass% Y2O3 ) production were developed and optimized. Electroconsolidated alumina and zirconia ceramics have higher values of properties in comparison with ordinary sintered samples in air. Advanced proper- ties of electroconsolidated ceramics are defined by homo- geneous, ultradense and fine-crystalline structure that was formed due to the effect to consolidate the materials to high density for a shortest time.
文摘The zirconia ceramic ring was prepared using fused monoclinic zirconia as main starting material, adopting composite stabilizer of magnesia, yttria and calcium nitrate, and applying recombination technology of traditional refractories and ceramics. Effect of the preparation process on material properties was comparatively studied, and the microstructure and phase composition were analyzed. The results show that adopting the high-speed mixing granulation process and the appropriate heat treatment can realize the control on the phase composition and microstructure, the zirconia ceramic ring with good thermal shock resitance and mechanical properties can be prepared.
文摘Wear resistance of several zirconia toughened ceramics in comparison with a metal-ceramic Co-WC has been studied in drawing wire field test. Result indicates that the harder the ceramic die, the longer the service life. Excellent wear resistance of ceramic die is obtained with a very high hardness (19 GPa). The service life is nearly three times that of Co-WC die. SEM observation on wear surfaces showed that material removal is mainly caused by plastic flow and ploughing process. But when the ceramic is composed of zirconia, alumina and some titanium carbide, micro-chipping and tribochemical reaction take place, and wear rate increases. Wear and friction induced martensite was detected by XRD. The T-M (tetragonal to monoclinic) phase transformation has a contribution to inhibiting microfracture.
基金Supported by the Henan Extraordinary Ability of China (No.0421001200)
文摘The performances of fine-crystalline zirconia ceramics in workpiece ultrasonic vibration grinding (WUVG) and conventional grinding (CG) with diamond wheel were researched. The effects of WUVG and CG on material removal rate, grinding forces, surface roughness and microstructure of zirconia ceramic were investigated. Experimental results indicated that: (1) The material removal rate (MRR) in ultrasonic grinding process is two times as large as that of in conventional grinding. The material removal rate increases with increasing grinding depth in both ultrasonic grinding and conventional grinding. (2) The ultrasonic vibration grinding force is lower than that of conventional grinding force, and the increase of the worktable speed leads to a decrease of the grinding force, while the grinding force increases with larger grinding depth in both WUVG and CG. (3) The surface of ultrasonic vibration grinding has no spur and build-up edge and its surface roughness is smaller than that of CG significantly. Surface quality of WUVG is superior to that of conventional grinding, it is easy for ultrasonic vibration grinding that material removal mechanism is ductile grinding.
基金Supported by National High Technology Research and Development Program of China(No.2002AA2040).
文摘Polycrystalline 3Y-TZP/Al2O3 tetragonal zirconia fiber was obtained by the pyrolysis of gel fibers using zirconium oxychloride octahydrate(ZOC) as the raw material. The spinnable zirconia sol was prepared by electrolyzing the zirco-nium oxychloride octahydrate(ZOC) solution in the presence of acetic acid and sugar( sucrose, glucrose or fructose) , in which the molar ratios of CH3 COOH/ZOC and sugar/ZOC were 1.0-4.0 and 0.2-0.4, respectively. The pre- pared tetragonal zireonia fibers sintered at different temperatures showed smooth and crack-free surfaces with diame, ters of 5-10 μm. The addition of Al2O3 enhanced the sintering process and prevented the crystals from growing. Thermogravimetric analysis(TG), X-ray diffraction ( XRD ), Fourier transform infrared spectroscopy(FTIR), and scanning electron microscope(SEM) techniques were used to characterize the prepared fibers.
基金The support of Gebze Technical University Scientific Research Council to project with a grant number BAP 2017A105-48
文摘The aim of this work was to investigate the microstructure and mechanical properties of 1vol%-Ni-added yttria-stabilized zirconia (YSZ) toughened alumina composites. First, Ni powders were heterogeneously precipitated in an alumina–zirconia powder mixture suspended in water;the prepared specimens were then pressureless sintered at 1550°C/2 h in a 90vol%Ar/10vol% H2 atmosphere. The structure of phases and microstructure of the composites were characterized by X-ray diffraction and scanning electron microscopy, respectively. Mechanical characterization of the specimens was carried out through Vickers hardness, Vickers indentation toughness, and three-point flexural bending tests. The fine Ni particles were homogeneously dispersed throughout the alumina matrix because of the employed processing method. Furthermore, hardness and toughness values were found to increase by 8% and 50%, respectively, with Ni addition, whereas the relative densities and flexural strength values were found to remain unchanged.
文摘The ZrO2-Al2O3 ceramic composites were prepared by appropriate techniques with commercial ZrO2 and Al2O3 powders as raw materials and Y2O3 as stabilizer. The results indicate that with the introduction of Al2O3 into the ZrO2 matrix where the quantity of additive Y2O3 is 3.5% (mole fraction), the growth of ZrO2 grains is efficiently inhibited, which helps the ZrO2 grains exist in a metastable tetragonal manner; thus higher strength and toughness are acquired. When the content of alumina is 20% (mass fraction), the bending strength and fracture toughness of the composites are 676.7 MPa and 10 MPa·m1/2 respectively, the mechanical behaviors are close to those prepared with ZrO2 and Al2O3 powders synthesized through wet chemical approach. The mechanical behaviors of the composites are well improved owing to the dispersion toughening of alumina grains and phase transformation toughening of zirconia grains.
文摘ntergranular slow crack growth in zirconia polycrystal is described with a cohesive zone model that simulate mechanically the reaction-rupture mechanism underlying stress and environ- mentally assisted failure. A 2D polycrystal is considered with cohesive surfaces inserted along the grain boundaries. The anisotropic elastic modulus and grain-to-grain misorientation are accounted for together with an initial stress state related to the processing. A minimum load threshold is shown to originate from the onset of the reaction-rupture mechanism to proceed where a minimum traction is reached locally and from the magnitude of the initial compression stresses. This work aims at providing reliable predictions in long lasting applications of ceramics.
文摘The present investigation demonstrated the comparative studies carried out on conventional, microwave and vacuum sintering of alumina added yttria stabilized zirconia (YSZ). The conventional, microwave and vacuum sintered specimens were characterized by density measurement, XRD, SEM with EDX analysis and hardness evaluation. Microwave sintering was proved to be the best efficient sintering technique with respect to energy and time savings. Enhanced densification was observed for the microwave and vacuum sintered specimens at lower temperatures compared to the conventionally sintered ones. Further, it was observed that the particle size had significant influence on the enhancement of densification. The microwave sintered specimen showed the highest hardness compared to conventional and vacuum sintered specimens.
文摘A novel method based on polyacrylamide gel process was used to prepare Li2O-Al2O3-SiO2 (LAS) glass-ceramic powders. The effects of ZrO2 addition on the crystallization and phase transformation process in LAS system were investigated by using differential thermal analysis (DTA), X-ray powder diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR). The activation energy decreases from 304.6 to 248.9kJ/mol and the frequency factor decreases from 2.49×10 11 to 5.56×108 min -1 as ZrO2 content changes from 0 to 4.0%(mass fraction). During calcination from 800 to 1200℃, hexagonal β-quartz solid-solution first crystallizes and then gradually transforms into tetragonal β-spodumene solid-solution with increasing temperature. The stability of β-quartz solid-solution increases with more ZrO2 additions and a minor crystalline phase, tetragonal zirconia, also appears.