akbar chami - Materials Engineering Department, Shahreza Branch, Islamic Azad University, Shahreza, Isfahan, Iran
Bahman Nasiri-Tabrizi - Materials Engineering Department, Najafabad Branch, Islamic Azad University, Najafabad, Isfahan, Iran

Due to the high hardness and wear resistance, electroless nickel-boron (Ni-B) coatings have found numerous applications. In the present study, the influence of the heating rate on the morphological features of oxidized electroless Ni-B coatings was investigated. The oxidation behavior of electroless coating layers was studied with TGA method under non-isothermal conditions at heating rates ۵, ۹ and ۱۳ °C/min. The phase compositions, elemental constituents and microstructural characteristics were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM) techniques, respectively. Results showed that the morphological features of the oxidized coating were influenced significantly by the heating rate so that under the heating rate of ۵ °C/min the morphology of oxidized layer was a porous film with an average pore size of around ۲ μm. With increasing the heating rate to ۹ °C/min, more recessed pores or intervals were gradually overlaid by a film. Further increasing the heating rate to ۱۳°C/min caused to the formation of polygonal protuberances on the surface.

Electroless plating, Ni-B, Morphological features, oxidation, Heating rate