The mode-converted (Longitudinal to Transverse, L-T) ultrasonic scattering was utilized to characterize the microstructural anisotropy on three surfaces of samples cut from the low-scattering and high-scattering regions of a raw titanium alloy Ti-6Al-4V billet, respectively. The L-T ultrasonic measurements were performed in two perpendicular directions using two focused transducers with a 15 MHz center frequency in a pitch-catch configuration. The root mean square (RMS) of ultrasonic scattering was calculated for each L-T measurement and a Gaussian function was used to fit each RMS to determine the RMS amplitude. The ratio of RMS amplitudes for L-T measurements performed in two perpendicular directions was calculated to characterize the microstructural anisotropy on the measured surface of a sample. The results show that the amplitude of L-T ultrasonic scattering is highly dependent on the microstructural anisotropy. The microstructural isotropy was considered on the x-y planes of all samples, while the high anisotropy was seen on the x-z and y-z planes of all low-scattering and high-scattering samples. In addition, the microstructural anisotropy measured on the x-z planes of the low-scattering and high-scattering samples gradually increases and decreases, respectively, from the outside diameter (OD) to the centerline (CL) of the billet. The anisotropy measured on the y-z planes of the low-scattering samples slightly decreases and then increases towards the center, while the anisotropy measured on the y-z planes of the high-scattering samples continuously increases towards the center. The variation of microstructural anisotropy in the titanium alloy Ti-6Al-4V billet with duplex microstructure was quantified with the L-T ultrasonic method and the results agree well with micrographs shown in Ref. [18]. The mode-converted ultrasonic scattering method provides a NDE method to characterize microstructural anisotropy, which can be used as an NDE tool for quality control.

利用模式转换（纵向到横向，LT）超声散射来表征分别从原始钛合金 Ti-6Al-4V 坯料的低散射区和高散射区切割的样品三个表面的微观结构各向异性。LT 超声测量是在两个垂直方向上进行的，使用两个聚焦换能器，中心频率为 15 MHz，采用一发一收配置。为每个 LT 测量计算超声散射的均方根 (RMS)，并使用高斯函数拟合每个 RMS 以确定 RMS 幅度。计算在两个垂直方向上进行的 LT 测量的 RMS 振幅比，以表征样品测量表面上的微观结构各向异性。结果表明，LT 超声散射的幅度高度依赖于微观结构的各向异性。考虑了微观结构的各向同性所有样品的x - y平面，而在所有低散射和高散射样品的xz和yz平面上都可以看到高各向异性。此外，在低散射和高散射样品的x - z平面上测量的微观结构各向异性分别从外径 (OD) 到坯料的中心线 (CL) 逐渐增加和减小。各向异性所测量ÿ - Ž低散射样品略微下降的平面，然后向中心增加，而各向异性所测量ÿ - ž高散射样品的平面向中心不断增加。具有双相微观结构的钛合金 Ti-6Al-4V 坯料微观结构各向异性的变化用 LT 超声方法量化，结果与参考文献中所示的显微照片非常吻合。[18]。模式转换超声散射方法提供了一种表征微观结构各向异性的无损检测方法，可用作质量控制的无损检测工具。