本文選題：X射線衍射層析成像　切入點：X射線三維成像　出處：《中國科學院研究生院(上海應用物理研究所)》2017年博士論文　論文類型：學位論文

【摘要】：硬多晶材料,例如金屬、合金和陶瓷,構成了多數(shù)現(xiàn)代工業(yè)的基礎。這些材料的物理、化學和機械性能在很大程度上取決于它們在晶粒尺度上的微結構及其相互作用。因此,對材料內微結構的表征成為了材料學研究領域的核心課題,同時,也是聯(lián)系材料設計與制造工藝的直接橋梁。傳統(tǒng)的結構表征方法在晶粒尺度上都存在一些局限性,例如:基于電子顯微學的表征方法只能用于晶粒的二維分布研究,且需要事先對樣品進行切片處理;基于實驗室光源的X射線衍射方法主要用于表征平均結構特性;顯微CT成像技術雖然是三維、無損的表征方法,但由于單相晶粒間的電子密度差異較小,從而難以獲得有效的襯度,無法獲得晶粒取向及三維空間分布信息。因此,迫切需要發(fā)展一種方法來實現(xiàn)材料內部晶粒的三維、無損、定量乃至動態(tài)微結構表征。本論文基于上海光源X射線成像線站建立了一種X射線衍射層析成像方法,可以用于材料內部晶粒的位置、尺寸、形貌、相、晶體學取向以及平均應變張量等信息的三維原位無損研究。本論文取得的創(chuàng)新性研究成果如下:基于上海光源X射線成像線站,成功搭建了X射線衍射層析成像實驗平臺,完成了軟件和硬件的調試,并利用立方晶系和六方晶系等標準樣品驗證了該方法的可行性。系統(tǒng)研究了各種因素對衍射層析成像質量的影響,并提出了相關優(yōu)化措施,具體包括:光子通量密度是造成精修操作中晶粒數(shù)量損失的主要原因;中值濾波可以有效抑制椒鹽噪聲的影響,改善尋峰的結果;優(yōu)值方法可以大幅提高校準的精度,結合并行化運算可以提高計算效率;對比度增強方法可以提高近場圖像的質量,改善尋峰和重建的結果。提出了一套不需要先驗知識來識別晶體第二相的方法,不僅可以原位無損的對第二相進行識別,同時還可以獲得各相晶粒的位置、尺寸、形貌和取向等信息。模擬研究和實驗研究結果驗證了該方法的可行性。模擬研究中建立了六個由不同晶系的主、次相組合的模型,結果表明該方法對于第二相的識別具有很好的普適性。實驗研究中,成功識別出VI系鋁合金樣品中的未知第二相為γ-Fe相,電子能譜分析和X射線顯微CT的結果進一步驗證了識別結果的正確性。實驗研究了合金晶粒信息與二次加熱溫度的關系。利用X射線衍射層析成像成功獲取合金內部晶粒的三維定量信息,包括:空間分布、體積、表面積、球度、取向、晶界取向差和織構等。對不同二次加熱溫度下VI系鋁合金樣品的定量分析結果表明:當溫度為640℃時,晶粒擁有最適合于觸變成形工藝的尺寸、形貌和取向:較大的晶粒數(shù)量、小而均勻的晶粒尺寸、較高的球度和隨機均勻分布的取向。
[Abstract]:Hard polycrystalline materials, such as metals, alloys and ceramics, form the basis of most modern industries. The physical, chemical and mechanical properties of these materials depend to a large extent on their microstructures at grain size and their interactions. The characterization of microstructure in materials has become the core subject in the field of materials science, and it is also a direct bridge between material design and manufacturing process. The traditional methods of structure characterization have some limitations in grain size. For example, the characterization method based on electron microscopy can only be used to study the two-dimensional distribution of grains, and the sample needs to be sliced in advance, and the X-ray diffraction method based on laboratory light source is mainly used to characterize the average structural characteristics. Although microscopic CT imaging is a three-dimensional, nondestructive characterization method, it is difficult to obtain effective contrast because of the small difference of electron density between single phase grains. Therefore, the information of grain orientation and three-dimensional spatial distribution can not be obtained. There is an urgent need to develop a method to characterize the three-dimensional, non-destructive, quantitative and even dynamic microstructure of the grains inside the material. In this paper, an X-ray diffraction tomography method is established based on the X-ray imaging line station of Shanghai Light Source. It can be used for the position, size, morphology and phase of grain in the material. Three-dimensional in situ nondestructive study of crystallographic orientation and average strain Zhang Liang. The innovative research results obtained in this paper are as follows: based on the X-ray imaging line station of Shanghai Light Source, an experimental platform for X-ray diffraction tomography has been successfully built. The software and hardware are debugged, and the feasibility of the method is verified by using cubic crystal system and hexagonal crystal system. The influence of various factors on the quality of diffraction tomography is systematically studied, and the relevant optimization measures are put forward. The results include: photon flux density is the main cause of grain number loss in finishing operation; median filter can effectively suppress the effect of salt and pepper noise and improve the result of peak finding; the accuracy of calibration can be greatly improved by the best value method. Parallel operation can improve the computational efficiency, contrast enhancement method can improve the quality of near-field images, and the results of peak finding and reconstruction can be improved. A method for identifying the second phase of crystals without prior knowledge is proposed. Not only can the second phase be identified in situ without damage, but also the position and size of each phase grain can be obtained. The results of simulation and experimental studies show that the method is feasible. In the simulation study, six models composed of main and secondary phases of different crystal systems have been established. The results show that the method has good universality for the recognition of the second phase. In the experimental study, the unknown second phase in VI aluminum alloy sample is successfully identified as 緯 -Fe phase. The results of electron spectrum analysis and X-ray microCT further verify the correctness of the identification results. The relationship between the grain information and the secondary heating temperature of the alloy is experimentally studied. The alloy is successfully obtained by X-ray diffraction tomography. Three dimensional quantitative information of internal grains, It includes: spatial distribution, volume, surface area, sphericity, orientation, grain boundary orientation difference and texture. The quantitative analysis results of VI aluminum alloy samples at different secondary heating temperatures show that: the temperature is 640 鈩，

本文編號：1574460