With the help of scanning electronic microscopy and X-ray diffraction, the relationships of microstructure characteristics, phase assemblage, and fracture micrograph of Al2O3/ZrO2 laminated ceramics were studied. Comp...With the help of scanning electronic microscopy and X-ray diffraction, the relationships of microstructure characteristics, phase assemblage, and fracture micrograph of Al2O3/ZrO2 laminated ceramics were studied. Compared with monolithic Al2O3/ZrO2 ceramics, the existence of surface compressive stresses greatly restrained the growth of ZrO2 and Al2O3 grains at high sinter temperature, fined the grain size, and increased the content of metastable t-ZrO2, which made the fracture transformation energy quantity 70% higher than that of the monolithic ceramics. The trans-granular and inter-granular fracture features were observed in the surface and center layers, which further verified that transformation toughening is the main mechanism, whereas, micro-crack toughening is helpful for enhancing fracture toughness.展开更多
Based on a constitutive law which includes the shear components oftransformation plasticity. the asymptotic solutions to near-tip fields of plane-strainmode I steadity propagating cracks in rransformed ceramics are o...Based on a constitutive law which includes the shear components oftransformation plasticity. the asymptotic solutions to near-tip fields of plane-strainmode I steadity propagating cracks in rransformed ceramics are obtained for the caseof linear isotropic hardening. The Stress singularity. the distributions of stresses andvelocities at the crack tip are determmed for various material parameters. The factorsinfluencing the near-tip fields are discussed in detail.展开更多
Toughness enhancement of zirconium tantalum ceramics is conducive to the new generation of thermal barrier coatings(TBCs).The phase transformation toughening mechanism of zirconium tantalum ceramics has been explored ...Toughness enhancement of zirconium tantalum ceramics is conducive to the new generation of thermal barrier coatings(TBCs).The phase transformation toughening mechanism of zirconium tantalum ceramics has been explored through the Vickers indentation of YTaO_(4) ceramic block,the phase transformation region is found near the indentation and the microcrack tip.The increased energy of stable phaseΔE_(M.M′)>0,and the volume expandedΔV≈1.9%,so,the phase transformation is a process of energy absorption.The additional stressσa restraining the crack propagation was generated in the shielding area at the crack tip.In addition,combined with the toughening of ferroelastic domains switch,the traditional microcrack toughening,and crack propagation toughening,we summarized the toughening mechanism of YTaO_(4) ceramics with the increasing external load,which is followed by ferroelastic toughening,phase transformation,microcrack,and crack propagation.For the perspective of toughening,we found that Z^(4+) doping in YTaO_(4) ceramics could broaden the phase transformation range in phase transformation toughening,significantly improve the toughness and reduce the generation of cracks in microcrack toughening and crack propagation toughening.Therefore,toughening mechanism of zirconium tantalum ceramics has important guiding significance for the service of TBCs.展开更多
The Al2O3-ZrO2（3Y）-SiC composite ceramics used in solar thermal power were prepared by micrometric Al2O3,nano-ZrO2 and SiC powders under the condition of pressureless sintering.The bulk density and bending strength ...The Al2O3-ZrO2（3Y）-SiC composite ceramics used in solar thermal power were prepared by micrometric Al2O3,nano-ZrO2 and SiC powders under the condition of pressureless sintering.The bulk density and bending strength of samples with 10vol% nano-ZrO2 sintered at 1480℃ were 3.222 g/cm3 and 160.4MPa,respectively.The bending strength of samples after 7 times thermal shock tests （quenching from 1000℃ to 25℃ in air medium） is 132.0MPa,loss rate of bending strength is only 17%.The effect of nano-ZrO2 content on the microstructure and performance of Al2O3-ZrO2（3Y）-SiC composite ceramic was investigated.The experimental results show that the bending strength of samples with above 10vol% nano-ZrO2 content has decreased,because the volume expansion resulting from t-ZrO2 to m-ZrO2 phase transformation is excessive;Adding proper nano-ZrO2 would be contributed to improve the thermal shock resistance of the composite ceramics.The Al2O3-ZrO2（3Y）-SiC composite ceramic has promising potential application in solar thermal power.展开更多
The effect of subzero treatment on the microstructure and mechanical properites of Y_2O_3- ZrO_2 ceramic have been investigated by TEM,X-ray diffraction and test of mechanical properties.It was shown that the microstr...The effect of subzero treatment on the microstructure and mechanical properites of Y_2O_3- ZrO_2 ceramic have been investigated by TEM,X-ray diffraction and test of mechanical properties.It was shown that the microstructre of 3Y-PSZ after subzero treatment by liquid nitrogen exhibits very long and parallel laths of m-phase and some microcracks around the larger and finer lath of m-phase may be discovered.Suitable subzero treatment can improve the strength and toughness of Y-PSZ efficiently because of decreasing the stability of t-phase and incresing the amount of t-m transformation when exerting a stress.However,when the time of subzero treatment exceeds,the over aging effect may arise.which can decrease the strength and toughness of the material.展开更多
基金This work was financially supported by the National Natural Science Foundation of China (No.59995440).
文摘With the help of scanning electronic microscopy and X-ray diffraction, the relationships of microstructure characteristics, phase assemblage, and fracture micrograph of Al2O3/ZrO2 laminated ceramics were studied. Compared with monolithic Al2O3/ZrO2 ceramics, the existence of surface compressive stresses greatly restrained the growth of ZrO2 and Al2O3 grains at high sinter temperature, fined the grain size, and increased the content of metastable t-ZrO2, which made the fracture transformation energy quantity 70% higher than that of the monolithic ceramics. The trans-granular and inter-granular fracture features were observed in the surface and center layers, which further verified that transformation toughening is the main mechanism, whereas, micro-crack toughening is helpful for enhancing fracture toughness.
文摘Based on a constitutive law which includes the shear components oftransformation plasticity. the asymptotic solutions to near-tip fields of plane-strainmode I steadity propagating cracks in rransformed ceramics are obtained for the caseof linear isotropic hardening. The Stress singularity. the distributions of stresses andvelocities at the crack tip are determmed for various material parameters. The factorsinfluencing the near-tip fields are discussed in detail.
基金supported by the National Basic Research Program of China(Grant Nos.11890684,52102142,and 12002054)the Foundation for Innovative Research Groups of Hunan Province(Grant No.2020JJ1005)the Innovation Capability Support Program of Shaanxi(Grant No.2022TD28)。
文摘Toughness enhancement of zirconium tantalum ceramics is conducive to the new generation of thermal barrier coatings(TBCs).The phase transformation toughening mechanism of zirconium tantalum ceramics has been explored through the Vickers indentation of YTaO_(4) ceramic block,the phase transformation region is found near the indentation and the microcrack tip.The increased energy of stable phaseΔE_(M.M′)>0,and the volume expandedΔV≈1.9%,so,the phase transformation is a process of energy absorption.The additional stressσa restraining the crack propagation was generated in the shielding area at the crack tip.In addition,combined with the toughening of ferroelastic domains switch,the traditional microcrack toughening,and crack propagation toughening,we summarized the toughening mechanism of YTaO_(4) ceramics with the increasing external load,which is followed by ferroelastic toughening,phase transformation,microcrack,and crack propagation.For the perspective of toughening,we found that Z^(4+) doping in YTaO_(4) ceramics could broaden the phase transformation range in phase transformation toughening,significantly improve the toughness and reduce the generation of cracks in microcrack toughening and crack propagation toughening.Therefore,toughening mechanism of zirconium tantalum ceramics has important guiding significance for the service of TBCs.
文摘The Al2O3-ZrO2（3Y）-SiC composite ceramics used in solar thermal power were prepared by micrometric Al2O3,nano-ZrO2 and SiC powders under the condition of pressureless sintering.The bulk density and bending strength of samples with 10vol% nano-ZrO2 sintered at 1480℃ were 3.222 g/cm3 and 160.4MPa,respectively.The bending strength of samples after 7 times thermal shock tests （quenching from 1000℃ to 25℃ in air medium） is 132.0MPa,loss rate of bending strength is only 17%.The effect of nano-ZrO2 content on the microstructure and performance of Al2O3-ZrO2（3Y）-SiC composite ceramic was investigated.The experimental results show that the bending strength of samples with above 10vol% nano-ZrO2 content has decreased,because the volume expansion resulting from t-ZrO2 to m-ZrO2 phase transformation is excessive;Adding proper nano-ZrO2 would be contributed to improve the thermal shock resistance of the composite ceramics.The Al2O3-ZrO2（3Y）-SiC composite ceramic has promising potential application in solar thermal power.
文摘The effect of subzero treatment on the microstructure and mechanical properites of Y_2O_3- ZrO_2 ceramic have been investigated by TEM,X-ray diffraction and test of mechanical properties.It was shown that the microstructre of 3Y-PSZ after subzero treatment by liquid nitrogen exhibits very long and parallel laths of m-phase and some microcracks around the larger and finer lath of m-phase may be discovered.Suitable subzero treatment can improve the strength and toughness of Y-PSZ efficiently because of decreasing the stability of t-phase and incresing the amount of t-m transformation when exerting a stress.However,when the time of subzero treatment exceeds,the over aging effect may arise.which can decrease the strength and toughness of the material.
