Improving Surface Properties of Inconel 600 Alloy by Electroless Ni-P Deposition

Abstract

The use of electroless Ni-P plating (EN) coating has attracted a surprising interest in the most recent years. Many useful characteristics of the electroless-plating method have created many benefits in different industries such as oil, gas, electronic, automotive, aerospace, and chemical. Some of the highlighted properties of such a method are superior corrosion resistance, superior mechanical properties, and uniform thickness of the coating as well as good surface finish properties, good adhesion characteristics, and a wide range of thickness. In this paper, electroless plating has been applied in a (Ni-P) bath at two different times of 2 and 3 hr respectively. After the plating, a heat treatment at 400 °C for an hour under vacuum 10-4 torr has been done. The prepared samples were characterized by energy dispersive spectroscopy, X-ray diffraction, and scanning electron microscopy (SEM). In addition, micro-hardness and corrosion rate following Tafel extrapolation in two acidic solutions (1M HCl and 1M H2SO4) were also determined. Vickers hardness values for specimens, coated by Ni -P at 2 and 3 hr have increased by 47 % and 32 % respectively. X-ray diffraction analysis for the coated surfaces showed two phases of Ni3P and NiP, presented before and after heat treatment. The SEM images of the cross sectional coated specimens revealed that the thickness of the coating is 68.43 and 92.71 µm for 2 and 3 hr coating time, respectively. Tafel analysis showed that the coated specimens had a lower corrosion current density compared to that for the bare specimens. The corrosion current density for the coated specimens in 1M H2SO4 increased by 57 % with 2 hr and 69 % at 3 hr coating time. While, the corrosion current density for the coated specimens in 1M HCl increased by 37 % and 83 % at 2 and 3 hr coating time respectively.