The effect of TiO2 concentration on morphology, wear and corrosion properties of NiB-TiO2 composite coatings by ultrasonic-assisted pulse electrodeposition

Abstract

In this study, TiO2 particle reinforced NiB alloy matrix composite coatings were produced on steel substrates by using a modified Watts type bath with ultrasonic-assisted pulse electrodeposition (UAPED) method. The average particle size of the TiO2 particles used in the composite coating is 500 nm, and the effect of different particle concentrations (0, 5, 10, 15 and 20 g l−1) on mechanical and electrochemical properties was investigated. The produced NiB alloy and NiB-TiO2 composite coatings were heat treated at 400 °C for 2 h, and the properties of the coatings were compared before and after heat treatment. Microstructure and morphology were characterized by scanning electron microscope (SEM). Phases and structures were determined by x-ray diffraction analysis (XRD), and crystalline size and % distortion were calculated from XRD analysis. The hardness measurements of NiB alloy and NiB-TiO2 composite coatings were carried out by microhardness measurement, and the wear tests of composites were carried out by the reciprocating method. Electrochemical measurements of coatings were carried out in 3.5% NaCl solution, and the effect of particle concentration on corrosion behaviour was investigated. The highest hardness value was 1268 HV, and it was obtained at 20 g l−1 TiO2 concentration and after heat treatment. The lowest crystalline size was obtained 34.4 nm with NiB-TiO2 composite coatings. When the wear resistances were compared with NiB-TiO2 composites and NiB alloy coating, composite coatings’ wear resistance increased approximately two times with the effect of heat treatment. In addition, when the coatings are evaluated in terms of corrosion behaviour, the best result was obtained in the composite coating produced with 20 g l−1 TiO2 concentration. Compared to NiB Alloy coating, the corrosion rate of the composite coating produced with 20 g l−1 TiO2 concentration was reduced from 32.49 mpy to 11.68 mpy. This indicates an improvement of approximately three times in corrosion rate.