Improvement of the atmospheric corrosion resistance of materials used in connectics. Surface treatments by ion implantation

Tests of corrosion of a material, constituted of brass covered with an electrochemical nickel coating (thickness approximate to 5 mu m) and with a gold coating (thickness approximate to 0.4 mu m or approximate to 1 mu m), used in electrical contact applications, have been carried out in humid synthetic air with low contents of NO2 (0.2 vpm), SO2 (0.2 vpm) and Cl-2 (0.01 vpm). The results obtained show that the corrosion products are well localised on the surface. The aggregates formed are principally constituted of basic nitrate, sulphate and chloride of nickel and zinc. These studies showed that the corrosion of the material is due to the presence of porosities in the gold and nickel layers. X-ray analysis (SEM/EDS) revealed the presence of carbon in these porosities, probably related to the presence of organic compounds in the electrolytic coating baths. During the galvanic corrosion of nickel and zinc, the carbon is rejected to the periphery of the aggregates. The amount of carbon was determined by Van De Graaff analysis, by (d,p) nuclear reaction. Some treatments of the material by ion implantation (titanium or titanium and nitrogen or helium) have been realised in order to suppress the porosities of the gold layer. These treatments lead to a remarkable improvement of the corrosion resistance of the material. (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.