基于第一性原理的WC-Co(0001)/cBN(111)界面结合性能研究

First-principles Study on Interface Bonding Properties of WC-Co(0001)/cBN(111)

基于第一性原理方法,建立WC-Co/cBN4B、WC-Co/cBN4N、WC-Co/cBN1B-near OA、WC-Co/cBN1N-near OA、WC-Co/cBN1N-near OB和WC-Co/cBN1B-near OB六种界面模型,计算其界面粘附功、断裂韧性。结果表明:WC-Co/cBN4B界面具有最大粘附功值9.705 J·m^-2,界面最稳定,粘附功大于WC(0001)w界面的断裂韧性7.824 J·m^-2,裂纹倾向于出现在基体中;WC-Co/cBN4N界面有最小粘附功4.470 J·m^-2,界面最不稳定,粘附功小于WC(0001)w界面的断裂韧性,裂纹倾向于出现在界面处。在此基础上,为从电荷转移、成键方式和价电子分布的深层次角度解释界面稳定性,进行了差分电荷密度、态密度和Mulliken布居分析,结果表明:WC-Co/cBN4B模型中,界面处Co、B原子之间存在电荷转移,由Co-d、B-p轨道杂化成强Co-B共价键;WC-Co/cBN4N模型中,界面处Co、N原子之间亦存在电荷转移,由Co-d、N-p轨道杂化成弱Co-N共价键。两种模型的界面处,Co-B共价键的布居数更大且键长更小、键能更大,Co-B共价键的作用强于Co-N共价键作用,因此,WC-Co/cBN4B界面结合性能更好,界面更稳定。

Based on the first-principles method,six interface models of WC-Co/cBN4B,WC-Co/cBN4N,WC-Co/cBN1B-near OA,WC-Co/cBN1N-near OA,WC-Co/cBN1N-near OB and WC-Co/cBN1B-near OB were established,then its interface adhesion work and fracture toughness were calculated.The WC-Co/cBN4B interface has the maximum adhesion work of 9.705 J·m^-2,and the interface is the most stable.The work is greater than the fracture toughness of the WC(0001)w interface of 7.824 J·m^-2,so the crack tends to appear in the matrix.While the WC-Co/cBN4N interface has the minimum adhesion of 4.470 J·m^-2,and the interface is the most unstable.The work is less than the fracture toughness of the WC(0001)w interface,so the crack tends to appear at the interface.Based on this,the charge density difference,density of states and Mulliken population analysis were carried out to explain the interface stability from the deep perspective of charge transfer,bonding mode and valence electron distribution.The results show that:there is charge transfer between Co and B atoms at the interface of WC-Co/cBN4B model,which is hybridized by Co-d and B-p orbital to strong Co-B covalent bond.There is also charge transfer between Co and N atoms at the interface of WC-Co/cBN4N model,which is hybridized by Co-d and N-p orbital to weak Co-N covalent bond.At the interface of the two models,the population of Co-B covalent bonds is larger,the bond length is smaller and the bond energy is larger.The effect of Co-B covalent bonds is stronger than that of Co-N covalent bonds.Therefore,WC-Co/cBN4B has better interface bonding performance and more stable interface.