Titanium carbide films obtained by conversion of sputtered titanium on high carbon steel

One the most important limitations to the industrial use of hard coatings in severe conditions is associated with their limited adhesion to the substrate. A number of research works have been done in various directions in order to improve the adhesion by post treatments such as laser remelting or thermal treatments. The aim of this work is to evaluate the possibility of using the substrate itself as a carbon source, in order to create very adherent hard titanium carbide coatings by means of a diffusion/precipitation process. A film of pure titanium was prepared by magnetron sputtering on a high carbon content steel substrate. Coated samples were then annealed in vacuum for 1 h at temperature ranging from 500 to 1100 °C. It was observed that the film was totally, partially or not transformed into titanium carbide, depending on heat treatment temperature. The transformation of titanium layer in titanium carbide takes place firstly at the interface between the film and the substrate, then it expands through the whole film thickness, toward the outer surface, by diffusion of carbon coming from the substrate. As a result, complete conversion of the titanium film in titanium carbide is obtained when an annealing temperature of 1100 °C is used. A higher adhesion, measured by means of a scratch tester, is found for this coating if compared to the one obtained on samples treated at lower temperatures and to other literature data on coatings having similar thickness and composition.