Influence of annealing on the structure and properties of carbon coatings containing Ti and TiN layers

Amorphous carbon (a-C) coatings are characterized by high internal stresses, relatively low thermal stability, low impact strength, poor adhesion to metal substrates, which limit their applicable scope. To eliminate these disadvantages doping with metals and heat-resistant compounds is used. Relaxation annealing and the introduction of sublayers are also used to modify the structure, predicted changes in the mechanical properties and the strength of the adhesive joint. Composite a-C coatings were deposited from the carbon plasma of the pulsed cathode-arc discharge and the flow of evaporated titanium atoms by a direct current arc in the nitrogen atmosphere at its partial pressure of 5 × 10−2 Pa. The AFM examination showed a change in the surface morphology after annealing and a decrease in surface roughness. Raman spectroscopy revealed an increase in the degree of misorientation of the carbon matrix after annealing at 350 °C, while a decrease in the size of the Csp2 clusters was observed for the Ti/a-C:Ti coatings. The XPS method established the effect of the annealing temperature on phase transformations, i.e. the formation of carbonitride compounds, which resulted in a higher rigidity of the carbon matrix, reducing the coating plasticity due to a decrease in the metal component and an increase in the concentration of oxide and carbonitride compounds. The indentation method proved a decrease in the hardness of the coatings containing TiN layers, while an increase in hardness for Ti/a-C:Ti was observed, which was associated with the structure change and an increase in the concentration of the TiC bonds. The sclerometry showed that the presence of titanium layers in the coating leads to an increase in the adhesion strength of the coating-substrate system. The TiN layers do not provide high adhesion to the a-C layers, which is associated with the limited ability of titanium atoms to interact with carbon atoms.