In order to discuss the effect of content of primary α on properties of bimodal microstructure, the TC4 sheet in rolling state was heat treated at different temperatures of 10~50°Cbelow the β-transus temperature, then a series of bimodal microstructures with different content of primary α were obtained by air-cooled procedure. Quasi-static and dynamic compress tests were carried out with universal material testing machine and Split Hopkinson Pressure Bar (SHPB) respectively. The results indicated that the relationship between mechanical properties and primary α is irregular, and that bimodal microstructure with 25% primary α shows a better combination of strength and ductility.
Adhesive is an important part of ceramic-metal composite armor. In order to obtain excellent ballistic performance, some adhesive with a variety of content of nano-SiO2 was prepared, and mechanical properties and ballistic test were conducted. The results show that the pores in adhesive decrease the strength of the adhesive, and the fracture happens along with the pores. To add nano-SiO2 in adhesive can decrease the porosity and the scale of the pores. In the ballistic performance, the adhesive enhance the acoustic impedance, the greater acoustic impedance can increase the energy of transmission wave and decrease the energy of reflection wave, leading to that the ceramic is destroyed slightly. The targets with adhesive added in 20% nano-SiO2 express the best anti-bullet properties. There are so many big blocks left in targets and the height of back convex is only 2.36mm.
2024Al and SiC/2024Al were used to encapsulate the AD95 Al2O3 ceramics by Vacuum-high Pressure Infiltration Method. Their anti-bullet properties are not good with Efm of 5.17 and 4.65 respectively, and is far lower than that of the ceramic without encapsulation. The latter one can generate higher hydrostatic pressure between the bullet and ceramic during penetration process. However, in encapsulated targets, the ductile materials in front of the ceramic can decelerate the bullet, so the pressure between bullet and ceramic is not great enough to break the bullet. Propagated microcracks along with the bonding interface were observed in plates consisting of encapsulated Al2O3. These microcraks lead to the interfacial debonding between Al2O3 and encapsulating materials. Consequently, the anti-bullet property of the ceramic encapsulated by metal or composite is depressed. Further more, the different interface bonding conditions and fracture modes cause the discrepancy of anti-bullet property in two kinds of targets with encapsulation structure.
The SiC3D/Al composite with high SiC content were prepared by vacuum– pressure infiltration process, and the prediction model of infiltration pressure threshold involving capillary pressure and viscous resistance was established. The effects of model parameters on the critical infiltration pressure were analyzed. The results show that the main factors are the permeability coefficient of SiC performs and the temperature of molten aluminum alloy. Temperature affects the melt viscosity and the wetting angle between SiC and molten alloy. The ingiltration pressure threshold of the specific infiltration system had been calculated by this model, which is in agreement with experimental results.
Carbon foam with relatively high compressive strength and high porosity was prepared from a mixture of mesophase pitch and Si particles by foaming and carbonization. The influence of Si content on the microstructures and properties of the carbon foam was studied. Results show that the pore number decreases and the strut thickness increases with an increasing of Si content. In addition, bulk density also increases with increasing Si content but the porosity decreases. Si addition to the mesophase pitch reduces the number of microcracks on the cell wall of the carbon foam remarkably which results in an increase of compressive strength for the carbon foams. Compressive strengths improve by 46%, 176% and 339% at Si additions of 30%, 40% and 50% (wt %), respectively. Carbon foam with a relatively high compressive strength of 24.6 MPa and a porosity of 61% are obtained when 50 wt% Si is added.
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