High-Temperature Mechanical Characterization of Laser-Machined Sapphire for High-Temperature Pressure Sensor Applications

摘要

iThe robust material properties of sapphire across a large temperature range make it an ideal material for pressure sensing at extreme temperatures; however, it is difficult to machine and requires specialized processes, such as laser ablation. Sapphire's thermomechanical properties are investigated to understand the influence of picosecond pulsed laser ablation processes on the elastic modulus and strength for temperatures ranging from room temperature to 1,300°C. Single crystal sapphire cut on the r-plane is tested using four-point bend bar specimens where thermomechanical properties in the as-received state are compared with properties after specimens are milled in the center region by the laser. Optical microscopy illustrates strong changes in the birefringence in the laser-machined region. Laser ablation results in a modulus reduction across all three temperatures tested while the strength increases. The modulus of laser-ablated sapphire is shown to be more resistant to temperature changes when operating below 950°C. The variability in strength also increased in the laser ablation specimens, which is promising for pressure sensor reliability. Bayesian statistics was used to assess differences in the elastic and strength properties as a function of both temperature and laser machining processes.