六方氮化硼韧脆转变性能的理论研究

A Theoretical Study on the Ductile-brittle Transition of Hexagonal Boron Nitride

基于六方氮化硼原子间Tersoff势函数,论文建立了手性依赖的六方氮化硼"杆-簧"模型,得到了其在大变形下的非线性力学行为.结果表明六方氮化硼断裂模式从扶手椅型(Armchair,手性角为0°)到锯齿型(Zigzag,手性角为30°)由韧性断裂转变为脆性断裂.通过分析拉伸过程中键长键角变化情况,键角变化所起作用超过键长变化导致韧性断裂,而键长起主导作用时则为脆性断裂.探讨不同手性氮化硼非线性力学行为,获得两种断裂模式的分界点大约为手性角15°.相同条件下,石墨烯在拉伸过程中键长变化起支配作用,而氮化硼除了键长变化的影响之外,键角的变化对整个过程也有着至关重要的作用.最后,与分子动力学模拟结果对比显示论文的理论结果是可靠的.该研究对理解六方氮化硼优异的力学性能及其在微纳器件领域的应用提供了理论支撑.

Based on the Tersoff potential,a stick-spiral model is developed to investigate the chirality-dependent nonlinear mechanical behavior of hexagonal boron nitride(h-BN).The chiral-dependent mechanism of ductile-brittle transition is revealed by extracting the changes of bond length and bond angle of h-BN under tensile loading.It is found that the ductile fracture of zigzag h-BN(ZZ,with the chiral angle of 30°) is dependent on the change of angle,while the brittle fracture of armchair h-BN(AC,with the chiral angle of 0°) is mainly caused by the change of bond length.Graphene,by contrast,is always dominated by the bond length during the tensile process.The critical chiral angle of ductile-brittle transition is found to be 15°.Compared with the molecular dynamics simulation,the present theoretical results have high accuracy.This study provides theoretical support for understanding the excellent mechanical properties of h-BN and can be of great help for its application in the field of micro-nano devices.