Corrosion resistance of electroless Ni-P-Al2O3 composite coating on low carbon steel in 3.5% sodium chloride solution

In this research, electroless Ni-P-Al2O3 composite coatings were prepared from the coating bath containing 5, 10, 15, 20 and 25g/l α-Al2O3 particles of 0.3 μm in size. The X-ray diffraction patterns of primitive coatings show a broad peak around 2θ of 45˚, which is an indication of an amorphous or an extremely fine crystalline structure. The results showed that the hardness and roughness of deposits are increased with increasing alumina content of the coating bath. Annealing at 400°C for an hour led the nature of deposits to be changed to crystalline phases of Ni and Ni3P and micro hardness values of the coatings are further increased. Electrochemical polarization curves and calculated corrosion values, revealed higher open circuit potential (Eocp) and lower corrosion current density for the coatings than for the bare substrate. The corrosion resistance of the coatings was further improved with increasing alumina content of the coating bath over the studied alumina concentration range of 5-25 g/l.

Corrosion resistance of electroless Ni-P-Al2O3 composite coating on low carbon steel in 3.5% sodium chloride solution Keywords:

Electroless Ni , P Composite coating , Alumina , Corrosion resistance , Polarization