Mechanical and electrochemical properties of ultrasonic-assisted electroless deposition of Ni-B-TiO2 composite coatings

Nickel-Boron-Titania (Ni-B-TiO2) composite coatings were successfully obtained on mild steel (St-37) by simultaneous electroless deposition. TiO2 particles were dispersed in a suspension by ultrasonic irradiation. The surface morphology, particle size, elemental composition and phase analysis of the coatings were characterized by scanning electron microscopy (SEM), inductively coupled plasma (ICP) and X-ray diffraction (XRD). The hardness and friction coefficient of as- plated and heat treated Ni-B and Ni-B-TiO2 composite coatings were determined by Vickers diamond indentation and indentation scratch tests and compared with Ni-B coatings. As a result, the hardness (1263 HV) of the as-plated Ni-B-TiO2 coatings was improved significantly. In addition, the corrosion resistance behavior of the as-plated and heat treated Ni-B and Ni-B-TiO2 coatings were analyzed by anodic polarization and electrochemical impedance spectroscopic (EIS) studies in a 3.5 wt.% NaCl solution. The as-plated composite coatings (Ni-B-TiO2) exhibited enhanced corrosion resistance (0.2 μA/cm2) property over Ni-B coatings.