Investıgatıon Of The Effects Of Coatıng Parameters On Corrosıon In Electroless Ni-B Coatıngs

Thesis Type: Postgraduate

Institution Of The Thesis: Gazi Üniversitesi, Fen Bilimleri Enstitüsü, Turkey

Approval Date: 2019

Thesis Language: Turkish




The aim of this study is to produce Ni-B coatings in coating baths with different reductant concentrations and to investigate the effects on the corrosion resistance and microstructure properties. For this purpose, the alkaline baths involving sodium borohydride (NaBH4) as reducing agent was used to deposit nickel–boron (Ni–B) on mild steel (St-37) samples. The surface and cross morphology, boron content, hardness and structure of the coatings were analyzed by field emission scanning electron microscopy (FESEM), inductively coupled plasma mass spectrometry (ICP-MS), nanoindentation and X-ray diffraction (XRD). In addition, the corrosion behaviors of the coatings were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5 wt.% sodium chloride (NaCl) solution. According to analyses, it was determined that the structure of the coatings is a mixture of microcrystalline nickel and amorphous Ni-B phases with columnar structure. The quantity of amorphous phase increased with boron content. The coatings produced with the optimum parameters determined have a cauliflower-like microstructure. The corrosion properties of the coatings were examined comparatively and with the increase of the reductant rate, the corrosion resistance was enhanced initially and thereafter started to decrease.