Treatment process for depositing a layer of carbon in vapour phase on the surface of a metal article and article thus obtained

Metal article comprising on at least a part of its surface a carbon layer produced by a treatment process for depositing a carbon layer, in vapor phase, in a vessel, to impart a resistance to frictional wear, a corrosion resistance, and a color, comprising the steps of:

• a) subjecting the surface of the article to a thermochemical pretreatment under electric plasma in the vessel under an atmosphere containing reactive species and hydrogen, the reactive species diffusing into and precipitating in the metal matrix of the article to form a diffusion sublayer, and
• b) depositing a layer of carbon in vapor phase on the surface thus treated, under electric plasma, in the same vessel, while gradually modifying the composition of the atmosphere of the pretreatment, on the one hand by introduction of a hydrocarbon and/or of a silane in the gaseous state and, on the other hand, by progressive reduction in the partial pressures of the reactive species employed during the pretreatment, and the maintenance of the hydrocarbon atmosphere for the carbon deposition,
• wherein said treated surface comprises a diffusion sublayer, a transition layer and a layer of amorphous hard carbon.