The effect of inhibitors on the corrosion and tribological characteristics of gray iron sliding against Si₃N₄ under lubricated conditions

In this study, Na₂SiO₃, Na₂MoO₄, (NH₂)NS and (NaPO₃)₆ were selected as inhibitors to slow down the corrosion of gray iron in distilled water. Furthermore, the wear tests of Si₃N₄-gray iron pair lubricated with these inhibited solutions were carried out on a ring-block tester. The worn surfaces of specimens were observed under SEM and optical microscope. The components and structure of tribofilm formed on the worn surfaces of specimens were analyzed by XPS. The results indicate that the Na₂SiO₃ inhibitor can effectively prevent the gray iron from corrosion when its concentration in distilled water ranges between 0.01 and 0.1 mol/l. In the wear tests of Si₃N₄-gray iron pair under 0.1 mol/l Na₂SiO₃ solution lubricated condition, the friction coefficient is as low as that of Si₃N₄-gray iron pair lubricated with distilled water. And the wear amounts of the Si₃N₄ and iron specimens are smaller than that lubricated with distilled water. The superior tribological characteristics are due to a tribochemical film formed on the wearing surfaces. The film consists of gel type amorphous SiO₂ and silicates and makes the paired surfaces smooth.