Functional mechanical part and its surface treatment method

A functional assembly comprising a first mechanical part comprising a first functional surface made of NiP and a second mechanical part comprising a second functional surface intended to be in frictional contact with the first functional NiP surface of said first mechanical part (2, 3), in which the first functional NiP surface comprises a layer of oxides and/or a layer of phosphates, respectively, the phosphate layer being a layer of Ni or of Zn phosphates, the frictional contact between the first and second mechanical parts being dry.