Pan Zicheng, Sun Hong, Zhang Yi, Chen Changfeng
Department of Physics, Shanghai Jiao Tong University, Shanghai 200030, China.
Phys Rev Lett. 2009 Feb 6;102(5):055503. doi: 10.1103/PhysRevLett.102.055503.
Recent indentation experiments indicate that wurtzite BN (w-BN) exhibits surprisingly high hardness that rivals that of diamond. Here we unveil a novel two-stage shear deformation mechanism responsible for this unexpected result. We show by first-principles calculations that large normal compressive pressures under indenters can compel w-BN into a stronger structure through a volume-conserving bond-flipping structural phase transformation during indentation which produces significant enhancement in its strength, propelling it above diamond's. We further demonstrate that the same mechanism also works in lonsdaleite (hexagonal diamond) and produces superior indentation strength that is 58% higher than the corresponding value of diamond, setting a new record.
最近的压痕实验表明，纤锌矿型氮化硼（w-BN）展现出令人惊讶的高硬度，可与钻石相媲美。在此，我们揭示了一种新颖的两阶段剪切变形机制，该机制导致了这一意外结果。我们通过第一性原理计算表明，压头下的大的法向压缩压力可在压痕过程中通过体积守恒的键翻转结构相变迫使w-BN转变为更强的结构，这使其强度显著增强，超过了钻石。我们进一步证明，相同的机制在六方金刚石中也起作用，并产生比钻石相应值高58%的优异压痕强度，创造了新纪录。
