复杂多晶材料的超声背散射微结构表征

With many excellent material properties, complex polycrystalline materials， which include grains with such as elongated single phase, duplex microstructure and their mix， are widely used in aerospace, nuclear industry, transportation, and petrochemical industry, etc. However, the microstructure and internal defects are one of the important factors that affect the mechanical properties and service life of the materials. Furthermore, characterizing precisely and evaluating effectively are the bottlenecks of the application of these materials. In this research, an ultrasonic nondestructive evaluation based on the ultrasonic backscatter theory is studied. Firstly, a corresponding theoretical ultrasonic backscattering model is deduced by analyzing spatial geometric structure of the complex polycrystalline materials’ grain. Then, an ultrasonic attenuation model for the complex polycrystalline material is developed with respect to an integration of the product of correlation function of the material and the covariance function of the scattering path. Introducing multi-Gaussian beam model, the effect of ultrasonic beam distortion on the ultrasonic scattering field is also discussed. Therefore, an improved ultrasonic backscattering theory model is developed for the complex polycrystalline material with the implementations of material grain size, phase distribution and dislocation microstructure characterization. Eventually, the progress of this research is decreasing inaccuracy of utilizing ultrasonic nondestructive testing on the material. It is anticipated to improve the quality and guarantee the safety, and to have scientific significance and valuable application.

复杂多晶材料（含拉伸单相晶、双相等轴晶和他们混合体的晶粒）具有许多优良材料特性，被广泛应用于航空航天、核工业、交通运输和石油化工等各领域，而微观组织结构和内部缺陷是影响其机械性能与服役寿命的重要因素，难以有效精准地无损表征微结构和内部缺陷是该材料在使用中面临的瓶颈问题之一。本项目拟研究一种基于背散射理论的复杂多晶材料中超声无损评价方法：首先分析复杂多晶的空间几何构造，推导相应的超声背散射的理论模型；通过对材料空间相关函数与超声散射路径的协方差乘积的积分，推导复杂多晶材料的超声衰减系数模型；引入多元高斯波束模型,研究超声波束畸变对背散射场的影响；最终建立复杂多晶材料的超声背散射理论模型，实现对材料晶粒尺寸、相分布和位错等微结构进行表征，最终突破超声无损检测对复杂多晶材料微结构表征不精准的难题。预期成果有助于提高复杂多晶材料的产品质量和保证其安全使用，具有重要的科学研究意义和应用价值。

复杂多晶材料（含拉伸单相晶、双相等轴晶和他们混合体的晶粒）具有许多优良材料特性，被广泛应用于航空航天、核工业、交通运输和石油化工等各领域，而微观组织结构和内部缺陷是影响其机械能与服役寿命的重要因素，难以有效精准地无损表征微结构和内部缺陷是该材料在使用中面临的瓶颈问题之一。超声波进入各向异性材料内部传播所产生的超声散射可以用于提取多晶材料的微结构信息。首先，推导了单/双探头一发一收式超声背散射理论模型，并通过拟合单探头一发一收式超声背散射理论模型与实验结果，成功提取了材料的晶粒的平均尺寸，结果显示较低频率的结果更优。为进一步优化结果，采用多元高斯声束代替现有的一元高斯声束，并进行了相关方面的数值分析。通过考虑含拉伸单相晶的微结构的超声背散射模型可以用来确定了含拉伸单相晶的铝合金材料的晶向尺寸。通过两垂直方向提取的超声背散射信号成功表征出不同程度各向异性含珠光体组织不锈钢。最后，考虑二次散射的复杂多晶超声背散射模型用于优化缺陷阀值的确定，从而提高缺陷检测率。该项目的成果有望提高为复杂多晶材料的超声无损检测与评估提供一种新的思路。

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