粉末合金具有无宏观偏析等突出优点，被广泛应用于航天、军工等高端领域，而晶粒度是影响其机械性能与服役寿命的重要因素，如何便捷有效地检测其晶粒度是当前的一个热点问题。本项目拟提出一种基于相速度的粉末合金构件晶粒度超声评价方法：制作不同晶粒度水平的粉末合金试块，研究粉末合金中超声相速度提取的算法，通过分析频率对相速度的影响规律，研究相速度提取的频段规划方法及频点选取策略。挖掘晶粒度与超声相速度之间的内在联系，揭示晶粒度对超声相速度的作用机理，利用灰色神经网络理论建立粉末合金晶粒度超声检测模型。构建模块化的多元高斯声场模型，研究基于该声场模型的超声衰减补偿算法，有效抑制粉末合金构件曲率及厚度引起的扩散损失。运用概率统计理论建立晶粒度评价参数体系，建立晶粒度的声图像表征及分析方法。预期研究成果为粉末合金晶粒度的超声检测提供理论依据，对提高粉末合金构件的产品质量与性能，保证其应用安全具有重要实际意义。

With distinct advantage of no macroscopic segregation, P/M alloy enjoys wide application in such high-end fields as aviation and military industries. Now that grain size is one of the most important factors affecting the mechanical performance and service life of P/M alloy, how to evaluate the grain size of P/M alloy components effectively attracts close attention nowadays. In this research, an ultrasonic evaluation method is proposed on the basis of phase velocity: P/M alloy test blocks of different grain sizes are produced to design the algorithm for extracting phase velocity in P/M alloy. Frequency band planning method and frequency selecting strategy are then studied by analyzing the influence of frequency on phase velocity. On the basis of GM neural network theory, internal relations between grain size and ultrasonic phase velocity can be obtained, influence mechanism of grain size on phase velocity can be observed, and the P/M alloy ultrasonic testing model can be established. The modularized multi-Gaussian beam modeling can be constructed for study of the compensation algorithm of ultrasonic attenuation based on the sound field model. In this way, the diffusion loss resulted from the geometry of P/M alloy components can be effectively restrained. The evaluation parameter system, the ultrasonic imaging characterization and corresponding analytical method of grain size can be established on the basis of probability statistics. This research aims to provide theoretical guidance for improvement of ultrasonic evaluation for the grain size of P/M alloy. The research results have important practical significance in regard to improvement of the quality and performance of P/M alloy components and guarantee of their application safety.