Tensile testing as alternative evaluation method for enhanced adhesion of diamond-like carbon coatings with different titanium buffer layers

Abstract

A tetrahedral amorphous carbon (ta-C) is widely used in industrial environments. However, application in extreme environments requires improved interfacial adhesion strength. This study proposes a new method to determine the adhesion strength of ta-C coating using the microtensile test, which is applied to improve the adhesion strength of ta-C coating by varying the Ti buffer layer microstructure. The tensile properties recorded in the stress-strain curve can be used to determine the difference between the absorbed energy and resistance to plastic deformation, which is then used to calculate fracture toughness. Moreover, to determine the adhesion strength, the crack density and spallation size were evaluated by measuring the cracks on the slip surface. The results show that compared to the columnar Ti buffer layer microstructure, the ta-C coating with a dense and flat Ti buffer layer microstructure more effectively improved the composite mechanical properties (columnar Ti layer H = ∼39 GPa, E = ∼430 GPa; dense Ti layer H = ∼48 GPa, E = ∼468 GPa), crack resistance (crack density = 6.4 % on columnar Ti layer; 1.5 % on dense Ti layer) and increased the dissipation energy during plastic deformation. Additionally, the dense Ti buffer layer microstructure reduced the wear rate (3.1 × 10−7 mm3/N∙m) and inhibited crack generation under long-term continuous frictional contact due to stress release in the ta-C coating. This finding clarifies the importance of the buffer layer with the suggested microstructural modifications for the wear resistance of ta-C coating.