Determination of fracture toughness of the thin diamond-like coatings by nanoindentation

Abstract

The results of a study of the structure and physical and mechanical properties of diamond-like coatings (DLC) on sublayers of different hardness are presented. The coatings have high hardness, but at the same time they are prone to delamination and destruction due to high residual internal stresses. The fracture toughness was determined by the nanoindentation method and the energy calculation method using approach-retraction curves. Atomic force microscopy was used to study the surface structure and deformation region after nanoindentation. A change in the surface structure and roughness of DLC was established depending on the sublayer. Low roughness is characteristic of DLC on a copper sublayer. Applying а titanium sublayer leads to an increase in the elastic modulus of the DLC. The microhardness of both coatings is practically the same. AFM studies have shown two different types of DLC deformation after nanoindentation with a Berkovich pyramid. A crack on coatings with a copper sublayer propagates around the indentation print, and on an DLC with a titanium sublayer, it propagates along the edges of the indentation. It was found that the fracture toughness of DLC on a Ti sublayer is 33 % lower compared to DLC on a Cu sublayer due to a decrease in stress relaxation inside the coating. The considered coatings can be used in microelectronics for protection against mechanical damage on contacting and rubbing surfaces.