采用太赫兹时域光谱技术的高精度热障涂层测厚方法

High-Precision Thermal Barrier Coating Thickness Measurement Method Using Terahertz Time-Domain Spectroscopy Technology

针对标准试块法测量热障涂层厚度需要制作标准试块导致成本高、测量工艺复杂、无法适应热障涂层服役后折射率变化等问题,提出了采用太赫兹时域光谱技术的高精度热障涂层测厚方法。首先,根据太赫兹波在热障涂层中的传播特性建立了热障涂层太赫兹波传播模型,通过模型可以得到太赫兹检测信号回波数量和回波相位对应的变化关系;然后,根据菲涅尔定律和太赫兹检测信号前3次回波之间的作用关系建立了折射率计算模型;最后,根据所得到的折射率和相邻两次回波时间差采用飞行时间法求解热障涂层厚度。对所提方法测量热障涂层厚度的可行性和准确性进行了多组实验研究,结果表明:与标准试块法相比,所提方法不需要制作标准试块,仅根据太赫兹检测信号即可同时计算得到热障涂层折射率与厚度,实现了对热障涂层高效、高精度测厚;所提方法测量厚度的相对误差可以达到1.15%,比标准试块法测量厚度的相对误差降低了42.5%。

In terms of the problems of the standard test block method,such as the high cost of making the standard test block,the complicated measurement process,and the inability to adapt to the change of the refractive index of the thermal barrier coating after service,a thermal barrier coating thickness measurement method based on terahertz time-domain spectroscopy is proposed.Firstly,according to the propagation characteristics of terahertz waves in thermal barrier coatings,a terahertz wave propagation model of thermal barrier coatings is established,and the relationship between the number of echoes and the phase of echoes of terahertz detection signals can be obtained through the model.Then,a refractive index calculation model is established according to Fresnel’s law and the interaction between the first three echoes of the terahertz detection signal.Finally,according to the obtained refractive index and the time interval between two adjacent echoes,the time-of-flight method is used to calculate the thickness of the thermal barrier coating.The feasibility and accuracy of the proposed method to measure the thickness of thermal barrier coatings are investigated by several groups of experiments.The results show that compared with the standard test block method,the proposed method does not need the making of a standard test block,and the refractive index and thickness of the thermal barrier coating can be calculated at the same time based on the terahertz detection signal,thus realizing the efficient and high-precision thickness measurement of the thermal barrier coating.The relative error of the proposed method can reach 1.15%,which is 42.5%lower than that of the standard test block method.