Nickel-boron electrochemical properties investigations

Electroless nickel-boron (Ni-B) was synthesized on mild steel. Coating thickness was approximately 30 μm. Some of the coatings were submitted to a hardening heat treatment at 400 oC for 1 h in an atmosphere containing 95% Ar and 5% H2 to improve their mechanical performance. Heat treated and untreated samples were submitted to the Taber abrasion test to assess their wear resistance. The wear track was then examined by SEM and roughness measurement. The Taber Wear Index of untreated samples was slightly better than that of steel but heat treated samples attained TWI as small as 13. The corrosion resistance of the Ni-B coatings was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. The EIS results showed diffusion phenomena in 0.1 M NaCl solution. Electroless Ni-B coating increases the corrosion resistance of steel and heat treatments allow a further enhancement. Wear decreases that resistance but the worn product keeps a better behaviour than uncoated parts.