The ceramic injection molding technique was used in the gas-pressure sintering of ultra-fine Si3N4 powder. The feedstock＇s flowability, debinding rate, defect evolution, and microstructural evolution during productio...The ceramic injection molding technique was used in the gas-pressure sintering of ultra-fine Si3N4 powder. The feedstock＇s flowability, debinding rate, defect evolution, and microstructural evolution during production were explored. The results show that the solid volume loading of less than 50vol% and the surfactant mass fraction of 6wt% result in a perfect flowability of feedstock; this feedstock is suitable for injection molding. When the debinding time is 8 h at 40°C, approximately 50% of the wax can be solvent debinded. Defects detected during the preparation are traced to improper injection parameters, mold design, debinding parameters, residual stress, or inhomogeneous composition distribution in the green body. The bulk density, Vickers hardness, and fracture toughness of the gas-pressure-sintered Si3N4 ceramic reach 3.2 g/cm^3, 16.5 GPa, and 7.2 MPa·m^1/2, respectively.展开更多
A kind of circular ring high frequency wideband underwater acoustic transducer is developed by using the Low Q value and broadband characteristics of the piezoelectricity composite material,and the dual mode coupling ...A kind of circular ring high frequency wideband underwater acoustic transducer is developed by using the Low Q value and broadband characteristics of the piezoelectricity composite material,and the dual mode coupling is used to broaden the bandwidth of the transducer by double ring stacking along the axial direction.Through theoretical analysis and simulation calculation,the geometric dimensions of the sensitive components are determined.The piezoelectric composite rings are processed and then the stack sensitive element can be made by stacking two piezoelectric composite rings with the same outer diameter and different thickness in axial direction by cutting piezoelectric ceramicsfilling the flexible polymer-coating electrode.Finally,the transducer can be made by pouring waterproof sound-permeable layer.The performances of transducer have also been tested in the water and the test results show that the resonant frequency is 410 kHz,the maximum transmit voltage response is 150 dB,the-3 dB bandwidth can reaches 60 kHz,the horizontal directivity（-5 dB） is 360°,and the vertical directivity（-3 dB） is 20°.It is also shown that the bandwidth of the transducer can be enlarged remarkably by using the method of stacking two different thickness piezoelectric composite rings along the axial direction,and the horizontal omnidirectional emission of acoustic wave can be realized展开更多
To achieve ultrasonic casting of 35 CrMo steel,the waveguide unit for introducing ultrasound into liquid steel was studied numerically and experimentally.The structure and length of the ultrasonic waveguide were optim...To achieve ultrasonic casting of 35 CrMo steel,the waveguide unit for introducing ultrasound into liquid steel was studied numerically and experimentally.The structure and length of the ultrasonic waveguide were optimized by modal analysis.The simulation results showed that a T-shaped waveguide unit matched the vibrational system better than an L-shaped unit.The performance of T-shaped waveguide unit was optimized when the length of the ultrasound radiator was 135 mm.The performance of the T-shaped waveguide unit was investigated in ultrasonic casting experiments,and the effect of ultrasound on the microstructure of 35 CrMo steel was examined.The experimental results showed that the T-shaped waveguide was able to successfully introduce ultrasound into the 35 CrMo melt.In addition,the use of a silicon nitride ceramic radiator avoided high-temperature corrosion in the molten metal.The microstructure of the treated area was significantly refined and equiaxed grains were obtained.The results represented a novel method for ultrasonic casting of steel.展开更多
基金financially supported by the National Nature Science Foundation of China (Nos. 51102024 and 21276028)
文摘The ceramic injection molding technique was used in the gas-pressure sintering of ultra-fine Si3N4 powder. The feedstock＇s flowability, debinding rate, defect evolution, and microstructural evolution during production were explored. The results show that the solid volume loading of less than 50vol% and the surfactant mass fraction of 6wt% result in a perfect flowability of feedstock; this feedstock is suitable for injection molding. When the debinding time is 8 h at 40°C, approximately 50% of the wax can be solvent debinded. Defects detected during the preparation are traced to improper injection parameters, mold design, debinding parameters, residual stress, or inhomogeneous composition distribution in the green body. The bulk density, Vickers hardness, and fracture toughness of the gas-pressure-sintered Si3N4 ceramic reach 3.2 g/cm^3, 16.5 GPa, and 7.2 MPa·m^1/2, respectively.
基金supported by the National Natural Science Foundation of China(614710470)
文摘A kind of circular ring high frequency wideband underwater acoustic transducer is developed by using the Low Q value and broadband characteristics of the piezoelectricity composite material,and the dual mode coupling is used to broaden the bandwidth of the transducer by double ring stacking along the axial direction.Through theoretical analysis and simulation calculation,the geometric dimensions of the sensitive components are determined.The piezoelectric composite rings are processed and then the stack sensitive element can be made by stacking two piezoelectric composite rings with the same outer diameter and different thickness in axial direction by cutting piezoelectric ceramicsfilling the flexible polymer-coating electrode.Finally,the transducer can be made by pouring waterproof sound-permeable layer.The performances of transducer have also been tested in the water and the test results show that the resonant frequency is 410 kHz,the maximum transmit voltage response is 150 dB,the-3 dB bandwidth can reaches 60 kHz,the horizontal directivity（-5 dB） is 360°,and the vertical directivity（-3 dB） is 20°.It is also shown that the bandwidth of the transducer can be enlarged remarkably by using the method of stacking two different thickness piezoelectric composite rings along the axial direction,and the horizontal omnidirectional emission of acoustic wave can be realized
基金Item Sponsored by National Basic Research Program of China(2014CB046702)
文摘To achieve ultrasonic casting of 35 CrMo steel,the waveguide unit for introducing ultrasound into liquid steel was studied numerically and experimentally.The structure and length of the ultrasonic waveguide were optimized by modal analysis.The simulation results showed that a T-shaped waveguide unit matched the vibrational system better than an L-shaped unit.The performance of T-shaped waveguide unit was optimized when the length of the ultrasound radiator was 135 mm.The performance of the T-shaped waveguide unit was investigated in ultrasonic casting experiments,and the effect of ultrasound on the microstructure of 35 CrMo steel was examined.The experimental results showed that the T-shaped waveguide was able to successfully introduce ultrasound into the 35 CrMo melt.In addition,the use of a silicon nitride ceramic radiator avoided high-temperature corrosion in the molten metal.The microstructure of the treated area was significantly refined and equiaxed grains were obtained.The results represented a novel method for ultrasonic casting of steel.
