题目：Atomistic characterization on the solute clustering and precipitation of Mg alloys
题目：Probing the heterogeneous nucleation interface of TiB2 in Al alloys
演讲人：Priv-doz. J.H. Li (李杰华教授奥地利莱奥本大学)
Institute of Casting Research, Montanuniversität Leoben, A-8700, Leoben, Austria
Magnesium alloys have important applications in the automotive and aerospace industries because of their high specific strength for the weight reduction and better fuel economy. However, the mechanical properties of conventional Mg alloys are often not suitable for high temperature applications. The addition of heavy rare-earth (HRE) elements can greatly improve the high temperature performance of Mg alloys, which can be directly correlated to the different type solute clusters and precipitates formed during the aged treatment. However, these solute clusters and precipitates have not been systemically characterized. Furthermore, there is a lack of the solute partitioning information into the precipitates. In this contribution, transmission electron microscopy (TEM) and atom probe tomography (APT) were employed to characterize the solute clustering and precipitates in Mg-Nd-Zn-Gd based alloys and Mg-Zn-Gd based alloys, respectively. TEM characterizations and APT analyses reveal that the roles of Gd are threefold: (i) forming Gd-containing ternary phase, and thereby partly consuming Gd, (ii) partitioning into the precipitates, and thereby increasing the number density of precipitates, decreasing the size of precipitates, and improving the thermal stability of precipitates, and (iii) increasing the eutectic temperature of the alloy, and thereby increasing the solution treatment temperature, dissolving more solutes into the Mg matrix, and enhancing the ageing hardening. These careful TEM characterizations and quantitative atom probe data analyses give us some hints to design novel Mg alloy and optimize some important Mg alloy in service.
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 TiB2in Al alloys, with a special focus on the partitioning of solute elements (Ti) to TiB2. A significant Ti partitioning to the whole surface of TiB2was unambiguously observed in the commercial grain refiner (Al-5Ti-1B. However, such prevalent Ti partitioning was not observed on the basal planes of TiB2in 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, CrB2was added together with TiB2. In this case, a significant Cr partitioning to the whole surface of TiB2was 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 TiB2and Al and further develops heterogeneous nucleation theory.
李杰华教授出生于1979年4月，2010年1月在西北工业大学获得工学博士学位。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。
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 Reports，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。