Effect of heat treatment on corrosion performance of electroless Ni-Mo-P deposit allay and studies of its anti-corrosive mechanism

Some methods of corrosion test were employed to test the corrosion performance (in 5% NaCl solution) of the Ni-Mo-P deposit alloy which was heat-treated in the range of 200-700��C. The result of static corrosion potential test showed that the potential of the deposit would be noble with increasing the temperature of heat treatment. From the point of view of thermodynamics, the stability of the deposit in corrosive media would increase. The results of corrosive rate test (dynamics) showed that the corrosion rate of the deposit increased first and then decreased with increasing the temperature of heat treatment. Anti-corrosion performance of the deposit would drop to a different degree in the range of 200-600��C. XRD, XPS and AES surface analysis techniques were used to investigate the mechanism of anti-corrosive performance which was affected by heat treatment. The result showed that the changes of lattice and phase in structure of the deposit alloy, the protective oxide film forming on the surface of the deposit alloy and the formation of the Fe-Ni-Mo-P diffusion layer between the deposit and the basis-metal played an important role in the changes of corrosion performance respectively in different ranges of heat treatment.