Electroless Ni-P and Ni-P-Al2O3 Nanocomposite Coatings and Their Corrosion and Wear Resistance

In an effort to utilize beneficial aspects of nanoparticles in providing corrosion and wear resistance, electroless Ni-P and Ni-P-Al₂O₃ nanocomposite coatings were produced. Alumina particles with various contents from 5 to 20 g/L in bath were co-deposited within Ni-P deposits on mild steel (ms) substrate. Coatings were characterized by scanning electron microscopy (SEM) for morphology, energy dispersive analysis of x-ray EDAX for analyzing elemental composition and x-ray diffractometry for investigating the structural changes of their components. Electrochemical and immersion measurements were used to analyze corrosion behavior of the coatings in 3.5% NaCl solution. Wear resistance of the coating was measured by pin-on-disc method. The results indicated that the Ni-P-Al₂O₃ coatings provide the high hardness as compare to the Ni-P coating. Corrosion and wear resistance of coatings is observed to be superior to that of ms. Corrosion protection properties of the coatings are found to be affected with continuous exposure to the electrolyte. Coating with high concentration of alumina is exhibiting high wear resistance than Ni-P coating. Wear mechanism in case of Ni-P coating appears to be adhesive type and seems to change to abrasive type on introduction of alumina.