高温钛合金轮盘是航空发动机核心部件之一，极端的运行工况对其内部缺陷检测提出了苛刻要求，而高温钛合金的强散射特性影响了微小缺陷的稳定检出，进而制约了高温钛合金轮盘设计制造水平的进一步提高。本项目拟研究一种高温钛合金轮盘的微小缺陷超声检测方法：首先，通过两相拉长晶的空间相关函数和织构模型，研究等温锻造轮盘超声多次散射响应机理；接着，考虑复杂型面下的声能分布，实现轮盘超声散射模型的曲率补偿；通过相依极值分布函数计算包络形式晶粒噪声的置信上限，以此作为超声检测的时变阈值实现超高灵敏度的微小缺陷识别；然后，探求晶粒噪声与缺陷回波相干叠加后信号幅值的莱斯分布，揭示晶粒噪声对缺陷回波的影响规律，建立时变的检测与定量不确定度计算模型；最终，用该模型优化超声检测工艺并实现微小缺陷的不确定度定量，得到缺陷尺寸的置信区间。预期成果可为有效检测高温钛合金轮盘的微小缺陷提供理论支撑，并服务于新一代航空发动机的研发。

High-temperature titanium alloy disc is one of the core components of aircraft engine. Strict detection of its internal defects is required under extreme operating conditions. The strong scattering properties of high-temperature titanium alloys make it difficult to detect internal small flaws reliably, which greatly restricts the level of design and manufacture of high-temperature titanium alloy disc. This project is aimed to investigate an ultrasonic method to detect small flaws in high-temperature titanium alloy discs. Firstly, the ultrasonic multi-scattering response model of isothermally forged disc is constructed by the spatial correlation function and texture model of two-phase elongated grains. Considering the distribution of acoustic energy under the complex surface of the disc, the ultrasonic scattering model is modified by the curvature compensation; the upper bound of the enveloped grain noise is calculated by the dependent extreme value distribution function, which is used as the time-dependent threshold of ultrasonic detection to be triggered by the flaw echo under ultra-high gain. Then, taking the coherent superposition of the grain noise and the flaw echo into account, the statistical feature of signal amplitude can be described by the Rician distribution. Based on the interaction between the grain noise and the flaw echo, we can obtain the time-dependent models for the probability of detection (POD) and probability of sizing (POS). Finally, the POD and POS models are used to optimize the ultrasonic detection process and improve the signal-to-noise ratio, to achieve accurate probability quantification of small flaw size, and to obtain the confidence interval of the flaw size. The achievements of this project are expected to provide theoretical support for the effective detection of small flaws in high-temperature titanium alloy discs and contribute to the development of next generation aircraft engines.