First-principles Study On The Influence Of Doping On The Strength Of Super-hard Materials

With the rapid development of modern science and technology, there's an increased demand for the hardness of materials. In the many properties of materials, hardness is one of the most important and basic index of performance. The synthesis and research of superhard materials have been given more and more attention.Since the discovery of diamond in the 19th century, people believed that diamond is the hardest material in the world. But in 2009, Professor Sun Hong found that two nanocomposites (W-BN and C-BN) can come up to the hardness of diamond. The two substances are both hexahedral structure, the resistance to pressure are from the elastic valence bond, which will turn into 90 degrees to reduce pressure.The purpose of this work is to investigate the effects of C, N, Si, O doping in W-BN. The double-faces stresses (vertical and tangential stress) of the measuring tool in the hardness experiments, especially the vertical pressure, are accounted for. It is the positive pressure that greatly enhances the shear strength. The strain is not obvious when the forces is weak, the intensity increased with the increase of the external force, but it decreased when the external force reaches a certain degree, but after that, the structure of the crystal shows a big change, causing a remarkable increase of the strength.