This study presents a general approach to derive the acoustic nonlinearity parameters induced by various types of dislocation configurations including dislocation strings （monopoles）, dislocation dipoles, dislocatio...This study presents a general approach to derive the acoustic nonlinearity parameters induced by various types of dislocation configurations including dislocation strings （monopoles）, dislocation dipoles, dislocation pileups and extended dislocations. It is found that expressions of the acoustic nonlinearity parameter induced by such a variety of dislocation con- figurations share a common mathematical form. They are all scaled with （Lch/b）n, where Lch is a characteristic length of the dislocation configuration, b is the magnitude of the Burgers vector, and n is either 3 or 4. Semiquantitative analysis is presented to compare the magnitudes of the acoustic nonlinearity parameters among different types of dislocation configurations.展开更多
The effects of Sr addition and pressure increase on the microstructure and casting defects of a low-pressure die cast （LPDC） AISi7Mg0.3 alloy have been studied. Metallographic and image analysis techniques have been...The effects of Sr addition and pressure increase on the microstructure and casting defects of a low-pressure die cast （LPDC） AISi7Mg0.3 alloy have been studied. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes and the amount of porosity occurring at different Sr levels and pressure parameters. The results indicate that an increase in the filling pressure induces lower heat dissipation of the liquid close to the die/core surfaces, with the formation of slightly greater dendrite arms and coarser eutectic Si particles. On the other hand, the increase in the Sr level leads to finer microstructural scale and eutectic Si. The analysed variables, within the experimental conditions, do not affect the morphology of eutectic Si particles. Higher applied pressure and Sr content generate castings with lower amount of porosiW. However, as the filling pressure increases the flow of metal inside the die cavity is more turbulent, leading to the formation of oxide films and cold shots. In the analysed range of experimental conditions, the design of experiment methodology and the analysis of variance have been used to develop statistical models that accurately predict the average size of secondary dendrite arm spacing and the amount of porosity in the low-pressure die cast AISiTMg0.3 alloy.展开更多
Strontium doped perovskite-type Nd0.7Sr0.3MnO3 ceramics were synthesized completely by high-energy ball milling raw oxides of Nd2O3, SrCO3 and MnO2. The optimal ball milling time and mass ratio of milling balls to raw...Strontium doped perovskite-type Nd0.7Sr0.3MnO3 ceramics were synthesized completely by high-energy ball milling raw oxides of Nd2O3, SrCO3 and MnO2. The optimal ball milling time and mass ratio of milling balls to raw materials are 4 h and 10：1, respectively. The grain size of as-milled Nd0.7Sr0.3MnO3 ceramics ranges from 51 to 93 nm, and the fine particles contain two phases of crystalline phase and amorphous phase. For the Nd0.7r0.3MnO3 synthesized by ball milling and sequent heat treatment, a remarkable colossal electroresistance （CER） effect is observed and the CER ratio reaches 900% at Curie temperature Tc when the load voltage increases from 0.1 to 0.8 V.展开更多
文摘This study presents a general approach to derive the acoustic nonlinearity parameters induced by various types of dislocation configurations including dislocation strings （monopoles）, dislocation dipoles, dislocation pileups and extended dislocations. It is found that expressions of the acoustic nonlinearity parameter induced by such a variety of dislocation con- figurations share a common mathematical form. They are all scaled with （Lch/b）n, where Lch is a characteristic length of the dislocation configuration, b is the magnitude of the Burgers vector, and n is either 3 or 4. Semiquantitative analysis is presented to compare the magnitudes of the acoustic nonlinearity parameters among different types of dislocation configurations.
文摘The effects of Sr addition and pressure increase on the microstructure and casting defects of a low-pressure die cast （LPDC） AISi7Mg0.3 alloy have been studied. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes and the amount of porosity occurring at different Sr levels and pressure parameters. The results indicate that an increase in the filling pressure induces lower heat dissipation of the liquid close to the die/core surfaces, with the formation of slightly greater dendrite arms and coarser eutectic Si particles. On the other hand, the increase in the Sr level leads to finer microstructural scale and eutectic Si. The analysed variables, within the experimental conditions, do not affect the morphology of eutectic Si particles. Higher applied pressure and Sr content generate castings with lower amount of porosiW. However, as the filling pressure increases the flow of metal inside the die cavity is more turbulent, leading to the formation of oxide films and cold shots. In the analysed range of experimental conditions, the design of experiment methodology and the analysis of variance have been used to develop statistical models that accurately predict the average size of secondary dendrite arm spacing and the amount of porosity in the low-pressure die cast AISiTMg0.3 alloy.
基金the National Natural Science Foundation of China (Grant No.10774040) and the joint Chinese-Russian Project for their financial supports
文摘Strontium doped perovskite-type Nd0.7Sr0.3MnO3 ceramics were synthesized completely by high-energy ball milling raw oxides of Nd2O3, SrCO3 and MnO2. The optimal ball milling time and mass ratio of milling balls to raw materials are 4 h and 10：1, respectively. The grain size of as-milled Nd0.7Sr0.3MnO3 ceramics ranges from 51 to 93 nm, and the fine particles contain two phases of crystalline phase and amorphous phase. For the Nd0.7r0.3MnO3 synthesized by ball milling and sequent heat treatment, a remarkable colossal electroresistance （CER） effect is observed and the CER ratio reaches 900% at Curie temperature Tc when the load voltage increases from 0.1 to 0.8 V.
