内华达州里诺大学Prof. Qi An 10月31日早上学术报告

Presenter：Prof. Qi An, University of Nevada, Reno

Topic：Brittle Failure of Boron Carbide and Related Materials from Atomistic Simulations; Strategy to Improve Ductility

Time：08：30AM, Oct. 31^st (Monday)

Location：909-B

Abstract

Ceramics such as boron carbide (B4C) are strong but too brittle for extended applications. The development of B4C based materials with improved properties is prevented by their complex bonding conditions and their relationships to the macroscale mechanical properties. In this talk we will discuss the deformation and brittle failure mechanism of B4C from atomistic simulations. We first identified a unique deformation path shearing along the most plausible slip system of (01)/<101> in which a boron-carbon bond between neighboring icosahedral clusters breaks to form a carbon lone pair (Lewis base) on the C within the icosahedron. Further shear then leads this Lewis base C to form a new bond with the Lewis acidic B in the middle of a CBC chain. This initiates destruction of this icosahedron, resulting in amorphous structure. Then we performed large-scale reactive-molecular-dynamics simulations on shear deformations of B4C and found that brittle failure in B4C arises from formation of higher density amorphous bands due to fracture of the icosahedra. This leads to negative pressure and cavitation resulting in crack opening. Furthermore, we will discuss the nano-twins in B4C, boron suboxide (B6O) and β-B, and their effects on the structural and mechanical properties. Finally we will discuss the microalloying strategies to improve the ductility of B4C by avoiding the icosahedral fracture.

Biography

Qi An is an assistant professor in Chemical & Materials Engineering Department at University of Nevada, Reno (UNR). He joined UNR in July 2016. Before then, he was a postdoctoral scholar in the Division of Chemistry and Chemical Engineering at Caltech. Qi An received his B.S. from University of Science and Technology of China, and his Ph.D. in Materials Science from Caltech in 2012. His research area is computational materials science. His research specifically focuses on material properties under extreme conditions; deformation and failure mechanism of superhard ceramics, metallic glasses, metals, and thermoelectric materials; detonation and sensitivity of energetic materials; and surface chemistry. He has authored or co-authored over 60 publications in the peer-review scientific journals.

Contact: Youyong Li

（责任编辑：张伶  联系方式：zhangling10@suda.edu.cn）