Presenter：Prof. Qi An,University of Nevada, Reno
Topic：BrittleFailure of Boron Carbide and Related Materials from Atomistic Simulations;Strategy to Improve Ductility
Time： 08：30AM, Oct. 31st (Monday)
Location：909-B
Abstract
Ceramics such as boron carbide (B4C)are strong but too brittle for extended applications. The development of B4Cbased materials with improved properties is prevented by their complex bondingconditions and their relationships to the macroscale mechanical properties. Inthis talk we will discuss the deformation and brittle failure mechanism of B4Cfrom atomistic simulations. We first identified a unique deformation pathshearing along the most plausible slip system of (0111)/<1101>in which a boron-carbon bond between neighboring icosahedral clusters breaks toform a carbon lone pair (Lewis base) on the C within the icosahedron. Furthershear then leads this Lewis base C to form a new bond with the Lewis acidic Bin the middle of a CBC chain. This initiates destruction of this icosahedron,resulting in amorphous structure. Then we performed large-scale reactive-molecular-dynamicssimulations on shear deformations of B4C and found that brittle failure in B4Carises from formation of higher density amorphous bands due to fracture of theicosahedra. This leads to negative pressure and cavitation resulting in crackopening. Furthermore, we will discuss the nano-twins in B4C, boron suboxide (B6O)and β-B, and their effects on the structural and mechanical properties. Finallywe will discuss the microalloying strategies to improve the ductility of B4C byavoiding the icosahedral fracture.
Biography
Qi An is an assistant professor in Chemical& Materials Engineering Department at University of Nevada, Reno (UNR). Hejoined UNR in July 2016. Before then, he was a postdoctoral scholar in theDivision 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 MaterialsScience from Caltech in 2012. His research area is computational materialsscience. His research specifically focuses on material properties under extremeconditions; deformation and failure mechanism of superhard ceramics, metallicglasses, metals, and thermoelectric materials; detonation and sensitivity ofenergetic materials; and surface chemistry. He has authored or co-authored over60 publications in the peer-review scientific journals.
Contact: Youyong Li
（责任编辑：张伶 联系方式：zhangling10@suda.edu.cn）
