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【百家大講堂】第312期:先進電子顯微學在物理冶金方面的應用

發布日期:2020-01-07

講座題目:先進電子顯微學在物理冶金方面的應用

報 告 人:陳江華

時   間:2020年1月9日(周四)9:00-11:30

地   點:中關村校區5號教學樓502-1

主辦單位:研究生院、材料學院

報名方式:登錄北京理工大學微信企業號---第二課堂---課程報名中選擇“【百家大講堂】第312期:先進電子顯微學在物理冶金方面的應用”

【主講人簡介】

  湖南大學教授、博士生導師、材料科學與工程學院院長,教育部“長江學者”特聘教授,國家千人計劃特聘專家,教育部首批“黃大年式教師團隊”負責人,教育部科技委材料學部委員,亞太材料科學院院士,湖南省政協常委。
  陳江華長期從事材料的微結構表征研究和先進電子顯微學技術的理論和方法學研究,是國內外知名電子顯微鏡專家和材料學家。他曾是世界上第一臺球差矯正電鏡樣機的測試研究員,為推動該先進電鏡的蓬勃發展作出過實質貢獻和建議。曾是歐洲波函數重構(電子全息)技術發展的參與者,回國后在湖南大學建立起有自己特色優勢的軟件矯正電鏡技術平臺并成功應用于鋁合金微結構測量表征。陳江華在電子顯微學理論和技術以及材料研究方面發表過150余篇論文和10項發明專利,其中以第一和通訊作者在Science發表過關于汽車車身用鋁合金材料的論文。主持過國家重大儀器研究、“973”研究計劃、高鐵列車車身材料可靠性和國產化等重大重點科研項目和課題。2016年獲“全國優秀科技工作者”稱號。擔任和曾擔任眾多全國學術組織的常務理事和國內外學術雜志編委。

 

Dr. Jianghua Chen has engaged in the field of transmission electron microscopy (TEM) for materials science for 35 years and mainly focuses on the development of TEM theories and methods for diffraction and imaging techniques, and on the TEM applications to materials research. Currently, he is the dean of the college of materials science and engineering and the director of the Center for High-Resolution Electron Microscopy (CHREM) at Hunan University, China.  Previously, he worked as a lecturer at Sichuan University for 8 years (1986--1994). Then he had worked in Europe for 14 years. Firstly in Belgium he did his Ph.D study and a postdoc job in the Electron Microscopy Lab at the University of Antwerp (1994--1998). Then in Germany he worked at Research Center Juelich for two years on the world first prototype Cs-corrected TEM. He then worked as a permanent senior scientist of the Netherlands Institute for Metals Research. After 2007, he gradually transferred his position from Holland to China.


Dr. Jianghua Chen established a few theories and methods for accurate and quantitative analysis of diffraction and imaging in TEM, and also developed a few techniques for achieving atomic-resolution imaging in modern TEM. Having mastered the advanced TEM instruments, he demonstrated as a pioneer how to determine the structures of small precipitates in aluminum alloys using quantitative atomic-imaging techniques. Based on the precisely determined precipitate structures, he revealed the quick-bake-hardening mechanism of the automotive AlMgSi alloys at the atomic-scale. Since then he solved many structure problems in metals. 


Dr. Chen holds 10 patents and has published more than 160 papers.  Due to his great contribution to electron microscopy for materials science, he has won many awards including the prestigious Distinguished Scientists Award 2016, granted by China Association for Science and Technology, and the honorable title of Chang Jiang Scholar Professor, granted by China Ministry of Education in 2008.

【講座信息】

  高強鋁合金中尺寸細小的早期強化相的成分、結構以及演變的表征尚存在難度,這一直以來限制著高強鋁合金的發展。我們的研究通過采用原子分辨率的透射電鏡(TEM)成像技術和第一性原理計算來解決這些問題。近年來,我們研究了大量典型的高強鋁合金,例如2xxx系、6xxx系和7xxx系合金,采用了不同的合金成分,并進行了不同的熱處理工藝,以便理解“性能-結構-工藝”之間的關系。結合球差矯正的高分辨TEM和球差矯正的掃描TEM(STEM),我們的主要關注點在于重新認識在這些重要的合金中出現的強化相以及闡明過去遺留下來的關于它們的析出行為的爭議。我們的研究表明:
  (1) STEM的原子分辨率成像技術可以在原子尺度提供直觀的析出相結構模型,但是HRTEM的原子分辨率成像技術具備快速定量的圖像模擬分析可能,可以提供超出電鏡的分辨率極限精度的精細的析出相結構。這兩種技術的結合可以更有效地解決材料科學中的顯微結構難題。
  (2) 鋁合金中大多數早期析出相的成分和結構都是高度動態的。隨著時效的進行,這些動態析出相的形核,成熟和生長通常遵循特定的演變路徑,并且有特征的基因骨架來引導它們各自的演變。我們的研究所揭示的精細的析出規律與目前所發表的教科書和文獻中的理解非常不同。

 

Developments of high-strength aluminum alloys have always faced a difficult problem: owing to their small size, the early-stage strengthening precipitates are difficult to characterize in terms of composition, structure and evolution. Here we employ atomic-resolution transmission electron microscopy (TEM) imaging and first-principles energy calculations to address these problems. Recent years, we have investigated tens of typical high strength aluminum alloys, such as 2xxx (AlCu, AlCuMg and AlCuLiMg), 6xxx (AlMgSi and AlMgSiCu) and 7xxx (AlZnMg and AlZnMgCu) alloys, with different compositions and with varying thermal processes for understanding their property-structure-process correlations. Using aberration-corrected high-resolution TEM (HRTEM) and aberration-corrected scanning TEM (STEM), much of our attention has been paid to revisit the strengthening precipitates in these important alloys and to clarify the controversies left in the past about their precipitation behaviors. Our study demonstrates the followings: 


(1) Atomic-resolution imaging in STEM can provide straightforward structure models at the atomic-scale, whereas atomic-resolution imaging in HRTEM with rapid quantitative image simulation analysis can provide the refined structures with high precision beyond the resolution limitation of the microscope. The combination of the two techniques can be more powerful in solving difficult structure problems in materials science.


(2) Most of the early-stage precipitates in aluminum alloys are highly dynamic in both composition and structure. Typically, having their characteristic genetic skeletons to guide their evolution, these dynamic precipitates initiate, mature and grow with thermal aging following characteristic evolution paths. The fine precipitation scenarios revealed in our studies are rather different from previous understandings in the textbooks and literatures published thus far.


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