Solute segregation at grain boundaries in ferrous alloys: approaches via experiments and simulations

Guest Speaker：Assistant Professor Yongjie Zhang，Tohoku University, Japan

Inviter: Assoc. Prof. Wei Li

Date&Time: Tuesday, 31.Dec., 9:30-11:00

Venue: Yiucheng Lecture Hall (500) , Xu Zuyao Building

 Biography:

Dr. Yongjie Zhang is an assistant professor at Institute for Materials Research (IMR), Tohoku University, Japan. He has graduated from Shanghai Jiao Tong University as a Bachelor in 2011, and received his Master and Ph.D degrees at Tohoku University in 2013 and 2016. During his Ph.D course, he worked as the Research Fellowship for Young Scientists (DC1) of the Japan Society for the Promotion of Science (JSPS). Currently, his research interests cover various fundamental aspects of microstructural control in steels, including nano-precipitation and strengthening, alloying effects on transformation kinetics, solute segregation at grain boundary, etc. So far, he has authored/co-authored several tens of high-level journal papers. Based on his research achievements, he has received multiple academic awards from the research societies, such as young researcher awards from the Japan Institute of Metals and Materials (JIM) and the Iron and Steel Institute of Japan (ISIJ), etc.

 Abstract:

Grain boundary segregation of solute elements plays a crucial role in determining the mechanical properties of polycrystalline metallic materials. Solute segregation behaviors are known to be strongly influenced by the grain boundary characters and the solute-solute interaction, which are important factors to consider for better controlling the grain boundary segregation for practical applications. In this study, these issues were investigated via different approaches either by experimental characterization or theoretical simulation. Through the combination of grain boundary crystallographic analysis using EBSD and compositional analysis using 3D-APT, P segregation in a high-purity Fe-P alloy was found to be facilitated with larger misorientation, whereas the further addition of C was found to be able to suppress the P segregation due to their strong repulsive interaction. On the other hand, topological analysis based on “persistent homology” was performed to identify the interstitial segregation site for C in a series of symmetrical tilt CSL grain boundary of BCC-Fe prepared by classic molecular mechanics, and the segregation energy of C calculated by DFT shows good correlation with the topological features of the grain boundary polyhedral units.