Preparation Of Laser Damage Resistant Ceramic Composite

With the development of high power laser system, tactical and strategic laser weapons are development rapidly, and they will be applied to actual combat soon,which will lay a serious threat to the missile, satellite,aircraft and other high value equipment.Therefore,it is particularly important to protect equipment against laser weapons.With the use of anti-laser materials we can reduce the threat from laser weapons effectively. So it is required that some materials not only have high laser-induced damage threshold, but also high structural strength and stability of high enough, and excellent high temperature resistance. The mullite ceramics,which featured with high mechanical properties, good thermal expansion,low coefficient of thermal conductivity, excellent high temperature creep characteristics and excellent chemical stability, can partly meet the performance requirements of the anti-laser material. But because of the structure of mullite itself, its intensity is low,and the reinforcement is necessary.It can improve the strength of mullite ceramics using method of hard phase toughened.In this paper, silica, alumina, silicon carbide and silicon nitride are used as raw material to prepare ceramics with good mechanical properties, and property of high laser-induced damage threshold. With the addition of silicon carbide and silicon nitride hard phase, we have achieved the ceramics with better mechanical properited sucessfully in the box-type resistance furnace in a nitrogen atmosphere. The influence of alumina and silica molar ratio changes, and changes of silicon nitride, silicon carbide content, sintering temperature and holding time on the structure and performance of ceramic composites are studied.The laser induced damage threshold of samples was tested by a femtosecond laser.Environmental scanning electron microscopy was used to observe the pulsed laser damage morphology of samples, as well as the bending section of the pore size, shape and distribution.The crystal phase is analyzed by X ray diffraction analysis.And the volume of the sample density, porosity, water absorption, and mechanical properties were tested and analyzed.The results of the study show that when the content of silicon nitride molar composition is2.44%, the sintering temperature is1600℃, sintering time is3h, the molar ratio of alumina and silica as3:2, the excellent performance of the ceramic can be achieved,the laser induced damage threshold is5.8J/cm2, the bulk density is2.65g/cm, the bending strength is110MPa, compressive strength is193MPa. When the molar content of silicon nitride increases to15%, while the SiC remains34%, we can achieve the best comprehensive properties as the composite ceramic has the comprehensive properties, the volume density is2.50g/cm3, the bending strength is157MPa, the compressive strength is290MPa, the laser induced damage threshold is1.99J/cm2. It also finds that the main damage mechanisms of femtosecond pulse laser are to stress damage nonthermal melting, heat melting and thermal expansion.