Improved SCC Properties of 70Cu-30Zn Alloy by Electroless Plated Ni-P/nano-TiO2 Composite Coatings in Fluoride Solutions

• Main Authors: Tsung-Yen Chan, 詹宗諺
• Other Authors: Cheng-Kuo Lee
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/97819017844389130659

碩士 === 清雲科技大學 === 機械工程所 === 100 === The present study used electroless plating techniques by adding nano-TiO2 in the plating solution with various concentrations of 1 g/L, 5 g/L, 10 g/L and 15 g/L to form Ni-P/nano TiO2 composite coatings on the 70Cu-30Zn brass alloy substrate. The corrosion resistance behavior was evaluated by potentiodynamic measurement and the susceptibility of the stress corrosion cracking (SCC) was evaluated by slow strain rate test (SSRT) in 0.1 M NaF solution. The surface morphology, element analysis and surface microhardness of the electroless Ni-P composite coatings were observed and analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and vicker’s microhardness tester. Experimental results indicated that the electroless Ni-P plating coating had a beneficial effect to enhance the hardness as well as corrosion and SCC resistance of brass alloy in 0.1 M NaF solution. When the nano-TiO2 particles added this beneficial effect was significantly raised with increasing the concentrations of nano TiO2 up to 15 g/L. The improved SCC resistance was attributed to the electroless Ni-P/nanoTiO2 composite coatings preventing the formation of an unstable Cu2O passive film for brass alloy in fluoride solution. This unstable passive film could be destroyed by strain and F- attack during slow strain rate tensile test, and resulting in dezincification dissolution and an intergranular stress corrosion cracking (IGSCC) of the brass alloy.