Adhesion at diamond/metal interfaces: A density functional theory study

To understand the basic material properties required in selecting a metallic interlayer for enhanced adhesion of diamond coatings on the substrates, the interfaces between diamond and metals with different carbide formation enthalpies (Cu, Ti, and Al) are studied using density functional theory. It is found that the work of separation decreases, while the interface energy increases, with the carbide formation enthalpy Delta H-f (Ti < Al < Cu). By comparing the work of separation at the interface with the work of decohesion of the metal, we found that the fracture is more likely to initiate in the metal phase near the interface; therefore a metal phase with a larger surface energy, gamma(s) (Ti>Cu>Al), is needed to achieve a higher overall interface strength. In addition, when the surface energy is larger than the interface energy, a wetted diamond/metal interface is formed during diamond nucleation, providing the strongest adhesion compared to other growth modes. These results indicate that a strong carbide-forming ability and a large surface energy of the interlayer promote nucleation and enhance the adhesion and interface strength of the coating/substrate system.