Influence of grain refinement on microhardness, wear behaviour and corrosion resistance of electrodeposited Ni-BN composite coatings

Abstract

The serviceability and efficiency of engineering materials can be improved by adopting a suitable surface modification technique. Ni/h-BN composite coatings were successfully coated over mild steel substrate by direct current electrodeposition at an optimised current density of 5 A/dm2 using Ni Watts bath. The current study explores the influence of grain refinement over microhardness, wear behaviour, and corrosion properties of Ni-BN coatings. The morphology and phase structure of the coatings were assessed by scanning electron microscopy (SEM) and X-ray diffractometry (XRD) respectively. Vickers microhardness tester and pin-on-disc tribometer were employed to evaluate the tribo-mechanical behavior of the coatings. Corrosion performance of the developed coatings was analysed using potentiodynamic polarization and electrochemical impedance spectroscopy techniques in 3.5 wt% corrosive NaCl medium. XRD results revealed that the average crystallite size of Ni-BN coatings reduced when the saccharin concentration rose from 0 to 5 g/l and stabilized around 21 nm. The microhardness of the Ni coating was enhanced by approx. 68 % with the inclusion 5 % saccharin and BN particles. An increment of 5.8730 × 104 Ω cm2 in the charge transfer resistance of the composite coating compared to Ni coating indicates its improved corrosion resistance. Ni–BN composite coatings offered lower coefficient of friction and wear mass loss than the pure Ni coating irrespective of saccharin incorporation. Surface modification of mild steel using electrodeposited Ni-BN composite coating significantly enhances the hardness, corrosion-resistance and wear-resistance, and thus extends service life and operational efficiency under demanding industrial conditions.