Based on the first-principles method, TiAlSiN/WC-Co interface models with graphene doped into the matrix, coating, and the coating/matrix are constructed. The interface adhesion work is calculated and modeled to study the interface bonding properties from the atomic microscopic point of view. The results show that the interface bonding properties of TiAlSiN/WC-Co can be improved when the matrix is doped with the main surface of intrinsic graphene, and the interface bonding property of TiAlSiNN/WC-Co can be improved when the coating and coating/matrix are doped separately with the main surface of intrinsic graphene or single vacancy defective graphene. Furthermore, the model electronic structures are analyzed. The results show that there exist strong Si/Co and N/Co covalent bonds in the interfaces when the matrix is doped with the main surface of intrinsic graphene, which causes the adhesion work of TiAlSiN/WC/msGR/Co to be greater than that of TiAlSiN/WC-Co. Additionally, when the graphene is doped into the coating, in the interface of TiAlSiN/msGR/TiAlSiNN/WC-Co, there exist strong N/Co covalent bonds that increase the interface adhesion work. Additionally, more charge transfer and orbital hybridization exist in the coating/matrix interface doped with the main surface of intrinsic graphene or single vacancy defective graphene, which explains the essential mechanism that the adhesion work of TiAlSiNN/msGR/WC-Co is greater than that of TiAlSiNN/WC-Co, and the adhesion work of TiAlSiNN/svGR/WC-Co is greater than that of TiAlSiNN/WC-Co.

In this paper, the unit cell model of V-doped TiN and TiAlN is constructed, and the formation enthalpy of the unit cell and lattice parameters of the doped models are calculated by first principles. The results show that the lattice parameters of TiN and TiAlN unit cells are reduced, and the structure of the unit cell is stable after V is doped into TiN and TiAlN unit cells. The structural stability of the TiN unit cell increases with V doping into the TiN unit cell, while that of the TiAlN unit cell decreases with the increase of V doping into the TiAlN unit cell. The analysis results of unit cell hardness and Mulliken population show that the hardness of TiN and TiAlN coating materials is improved by doping V and that hardness increases with the increase of V doping. The reason is that V doping into TiN and TiAlN unit cells increases their average bond population. The covalent bonding property of the unit cell is increased, and the interatomic bonding strength of the unit cell is increased, which leads to an increase in the unit cell’s hardness.

The interface models of diamond-coated WC-Co cemented carbide (DCCC) were constructed without intermediate layers and with different interface terminals, such as intermediate layers of TiC, TiN, CrN, and SiC. The adhesion work of the interface model was calculated based on the first principle. The results show that the adhesion work of the interface was increased after adding four intermediate layers. Their effect on improving the interface adhesion performance of cemented carbide coated with diamond was ranked in descending order as follows: SiC > CrN > TiC > TiN. The charge density difference and the density of states were further analyzed. After adding the intermediate layer, the charge distribution at the interface junction was changed, and the electron cloud at the interface junction overlapped to form a more stable chemical bond. Additionally, after adding the intermediate layer, the density of states of the atoms at the interface increased in the energy overlapping area. The formant formed between the electronic orbitals enhances the bond strength. Thus, the interface bonding performance of DCCC was enhanced. Among them, the most obvious was the interatomic electron cloud overlapping at the diamond/SiCC-Si/WC-Co interface, its bond length was the shortest (1.62 Å), the energy region forming the resonance peak was the largest (−5–20 eV), and the bonding was the strongest. The interatomic bond length at the diamond/TiNTi/WC-Co interface was the longest (4.11 Å), the energy region forming the resonance peak was the smallest (−5–16 eV), and the bonding was the weakest. Comprehensively considering four kinds of intermediate layers, the best intermediate layer for improving the interface bonding performance of DCCC was SiC, and the worst was TiN.

This study performed first-principle-based calculations of the interface adhesion work in interface models of three terminal systems: CrAlSiNSi/WC-Co, CrAlSiNN/WC-Co, and CrAlSiNAl/WC-Co. The results proved that the CrAlSiNSi/WC-Co and CrAlSiNAl/WC-Co interface models had the highest and lowest interface adhesion work values (4.312 and 2.536 J·m−2), respectively. Thus, the latter model had the weakest interface bonding property. On this basis, rare earth oxides CeO2 and Y2O3 were doped into the Al terminal model (CrAlSiNAl/WC-Co). Then, doping models of CeO2 and Y2O3 doped on the WC/WC, WC/Co, and CrAlSiNAl/WC-Co interfaces were established. The adhesion work value was calculated for the interfaces in each doping model. When CeO2 and Y2O3 were doped in the WC/WC and CrAlSiNAl/WC-Co interfaces, four doping models were constructed, each model contains interfaces withreduced adhesion work values, indicating deteriorated interface bonding properties. When the WC/Co interface was doped with CeO2 and Y2O3, the interface adhesion work values of the two doping models are both increased, and Y2O3 doping improved the bonding properties of the Al terminal model (CrAlSiNAl/WC-Co) more significantly than CeO2 doping. Next, the charge density difference and the average Mulliken bond population were estimated. The WC/WC and CrAlSiNAl/WC-Co interfaces doped with CeO2 or Y2O3, with decreased adhesion work, exhibited low electron cloud superposition and reduced values of charge transfer, average bond population, and interatomic interaction. When the WC/Co interface was doped with CeO2 or Y2O3, superposition of the atomic charge densities of electron clouds was consistently observed at the CrAlSiNAl/WC-Co interface in the CrAlSiNAl/WC/CeO2/Co and CrAlSiNAl/WC/Y2O3/Co models; the atomic interactions were strong, and the interface bonding strength increased. When the WC/Co interface was doped with Y2O3, the superposition of atomic charge densities and the atomic interactions were stronger than for CeO2 doping. In addition, the average Mulliken bond population and the atomic stability were also higher, and the doping effect was better.