Temperature-dependent modeling and enhanced measurement of ultrasonic velocity in LAS glass–ceramics

Li₂O-Al₂O₃-SiO₂ (LAS) glass-ceramics are widely used in many fields owing to their ultra-low coefficient of thermal expansion (CTE). The ultrasonic velocity method shows potential as an effective method for the nondestructive measurement of the CTE and CTE homogeneity of large LAS glass-ceramics. To further improve the precision of ultrasonic velocity (c_L) measurements of LAS glass-ceramics and reveal the effect of the temperature (T) on c_L, an improved correlation method to rapidly determine the time of flight (TOF) in LAS glass-ceramics is proposed. The proposed method significantly reduces the calculation time by a factor of 100 for LAS glass-ceramics with a thickness of 50 mm. Furthermore, the TOF results obtained by this method were compared with those obtained by the commonly used peak and zero-crossing methods. The proposed correlation method showed better TOF repeatability precision (0.69 ns). Considering the effect of T on the precision of the c_L measurement, a c_L-T exponential model was developed based on the theoretical c_L-T analytical model. The accuracy of the c_L-T exponential model was experimentally verified. The root-mean-square error was within 0.30 m/s, which shows that the developed exponential model can reliably predict the c_L values of LAS glass-ceramics at different temperatures. The two meaningful findings mentioned above provide methodological and modeling support for high-precision nondestructive CTE testing of large LAS glass-ceramics at specific temperatures.