SiO_2薄膜对蓝宝石表面及高温强度的改善

Improving on Surface and High-temperature Strength of Sapphire by SiO_2 Films

蓝宝石具有一系列优异的光学和力学性能,使其成为红外透过窗口与头罩中备受青睐的材料．然而随温度的升高蓝宝石沿c轴的抗压强度急剧降低,大大限制了蓝宝石的抗热震等许多性能．提高蓝宝石高温强度的研究已成为蓝宝石在高速、高温应用中一个亟待解决的重要课题．本文采用射频磁控反应溅射法在蓝宝石衬底上制备了SiO2涂层．利用三点弯曲法测试了镀膜及未镀膜蓝宝石试样的室温及高温抗弯强度,测量了镀膜前后蓝宝石试样的表面形貌及粗糙度,采用压痕裂纹法分析了镀膜前后蓝宝石的表面残余应力．结果表明,镀SiO2薄膜可以改善蓝宝石的表面形貌,降低表面粗糙度,同时改变蓝宝石的表面应力．在800℃,镀膜蓝宝石的抗弯强度是未镀膜蓝宝石的1．5倍．

Sapphire is a desired material for infrared-transmitting windows and domes because of its excellent optical and mechanical properties. However, its thermal shock resistance is limited by loss of compressive strength along the c-axis of the crystal with increasing temperature. Research and development work for increasing the high temperature strength of sapphire is a major problem with sapphire in high-speed or high-temperature applications. In this paper, SiO2 coating was prepared on sapphire substrate by RF magnetron reactive sputtering. The flexure strength of sapphire sample uncoated and coated with SiO2 was studied by 3-point bending tests at room temperature and high temperatures. Surface morphology and roughness of coated and uncoated sapphire were measured. Surface residual stress of sapphire substrate and sapphire coated with SiO2 film was estimated by using pointed-indentation cracking under Vickers indenters. The results show that SiO2 coating can improve both the surface morphology and roughness of sapphire. At the same time, the SiO2 coating can change the surface residual stress of sapphire. Results for 3-point bending tests show that the SiO2 coating increases the fracture strength of c-axis sapphire by a factor of about 1.5 at 800℃.