Susceptibility to Stress Corrosion Cracking and Electrochemical Behavior of Electroless Ni-P ano-TiO₂ Composite Coatings on 70-30 Brass in Fluoride Solutions

摘要

In this investigation, electroless plating techniques were utilized to form Ni-Pano-TiO2 compositecoatings on a 70-30 brass alloy substrate by adding nano-TiO2 to the Ni-P plating solution inconcentrations of 1 g/L, 5 g/L, 10 g/L and 15 g/L. The electrochemical corrosion resistance behavior ofthese composite coatings and their susceptibility to stress corrosion cracking (SCC), which wererelated to their surface morphology and microstructure were studied by comparing them with those ofan Ni-P coating. Experimental results revealed that the electroless Ni-P plating coating increased thehardness and the resistance to corrosion and SCC of the brass alloy in 0.1 M NaF solution. When nano- TiO2 particles were added, this beneficial effect increased significantly with their concentration up to15 g/L. The improved SCC resistance was attributed to the electroless Ni-Pano-TiO2 compositecoatings, which prevented the formation of an unstable Cu2O passive film on brass alloy in fluoride- solution. This unstable passive film was destroyed by tensile strain and F attack during tensile testingwith slow strain in fluoride solution, resulting in dezincification dissolution and intergranular stresscorrosion cracking (IGSCC) of the brass alloy.