报告题目(中文)：铝合金中TiB2异质形核界面探究

报告题目(英文)：Probing the heterogeneous nucleation interface of TiB2 in Al alloys

报告内容简介：The grain refinement of Al alloys has been extensively investigated for several decades both in industry and academia, not only through attempts at developing efficient grain refiners, but also with a view to achieve a better understanding of the grain refinement mechanism. The addition of Al-Ti-B grain refiners (e.g. Al-5Ti-1B, wt. %) during the grain refinement of Al alloys has been widely investigated due to these compounds’ higher nucleation potency and wide potential for industrial applications. Various theories regarding the grain refinement mechanisms of Al-Ti-B refiners have been proposed. Despite differences between all these theories, it is generally accepted that Ti has multiple roles within the Al melt. One role is to create an enriched Ti region leading to the formation of an Al3Ti monolayer necessary for the heterogeneous nucleation of Al on the stable boride substrates (TiB2). The other role is to act as an effective growth restrictor factor. It is the combined effects of the enhancement in nucleation site numbers and of the growth restrictions that result in the formation of desirable, small uniform equiaxed Al grains. It is well accepted that Ti is more likely to segregate to the TiB2 / α-Al interface affecting its structure and thereby the constitutional undercooling at the solid-liquid interface. The presence of the Al3Ti monolayer is still fervently disputed. To resolve this disagreement, an atomic scale experimental investigation on the heterogeneous nucleation interface between TiB2 and α-Al in conventional castings (e.g. in alloys containing < 0.15 wt. % Ti that have not been melt spun) would be required. This talk employs atomic scale high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) imaging and electron energy loss spectroscopy (EELS) to probe the heterogeneous nucleation interface of TiB2 in Al alloys, with a special focus on the partitioning of solute elements (Ti) to TiB2. A significant Ti partitioning to the whole surface of TiB2 was unambiguously observed in the commercial grain refiner (Al-5Ti-1B. However, such prevalent Ti partitioning was not observed on the basal planes of TiB2 in Al-Si based alloys with high Si concentrations, which could be used to explain why Si poisoning occurs. In order to avoid / reduce the Si poisoning, CrB2 was added together with TiB2. In this case, a significant Cr partitioning to the whole surface of TiB2 was observed, which may minimize the lattice mismatch with Al and / or improve the stability of an Al3Ti monolayer on TiB2. This investigation provides a clearer picture about the heterogeneous nucleation interface between TiB2 and Al and further develops heterogeneous nucleation theory.

报告人姓名：李杰华

报告人简介(中文)：李杰华教授出生于1979年4月，2006年4月在西北工业大学获得工学硕士学位，2010年1月在西北工业大学获得工学博士学位，2008年7月到2009年8月，在澳大利亚悉尼大学作为联合培养博士生。从2010年2月开始，一直在奥地利莱奥本大学 (Montanuniversitaet Leoben) 铸造研究所 (Chair of Casting Research) 从事教学和科研工作，并于2014年7月，被提升为高级讲师 (Senior Lecturer), 于2015年5月，取得奥地利莱奥本大学Habilitation教授及博导资格，被提升为Privatdozent。 李杰华教授精于金属材料凝固理论及铸造工艺与设备的研究，先后申请并完成2项奥地利科学基金（FWF）项目，3项奥地利研究促进会(FFG)项目，以及20余项与欧洲著名铸造企业(G.F.，Nemark，SAG，Aleris，BMW，Audi，Bühler，Voestalpine)合作项目。李杰华教授以第一作者和唯一通讯作者在金属材料凝固与铸造领域国际顶尖和主流学术期刊上发表34篇学术论文，包括2篇Scientific Report，6篇Acta Mater.，4篇Metallurgical and Materials Transactions A.，2篇Philosophical Magazine，1篇Journal of Materials Science，1篇Materials Characterisation，3篇Material Science and Engineering A，1篇Nanoscale。另外，李杰华教授拥有两项中国发明专利和一项美国发明专利。李杰华教授担任多个国际金属材料领域顶尖和主流期刊的评审(Material Science and Engineer A (2011-), Material Science and Engineer B. (2012-), Journal of Alloys and Compound (2014-), Thermochimica Acta (2014-), Engineering Review (2014-), Material Characterization (2015-), Acta Metallurgica Sinica (英文版) (2015-)，Material and design (2015-)， Transactions of Nonferrous Metals Society of China (英文版) (2016-present)，Encyclopedia of Aluminum and Its Alloys (2016-present), Metals (2016-present), Philosophical Magazine (2016-present)), Advances in Materials Science and Engineering (2016-present)。

报告人单位(中文)：奥地利莱奥本大学

报告时间：2016-06-24 14:30

报告地点：延长校区　日新楼410室