Development of Electroless Ni-P-Cu Composite Coating: A Characterisation, Corrosion and Thermal Study on AISI-1040 Used in Heat Exchangers

Abstract

Electroless coating is such an area that has recently taken the research spotlight. Heat exchangers are the most used industrial equipment by chemical and mechanical firms. Of various other materials like copper, iron and carbon steel, it is considered that the structural units of these heat exchangers should be mild steel because the other metals are more porous in nature, encouraging corrosion, scaling and fouling. Mild steel is a revolutionary material that has a varied range of uses, from tiny needles to giant machinery. Easy market availability, material durability, great thermal efficiency and reasonable prices are the core reasons for this. However, the material has a few crucial disadvantages like corrosion, wear, fouling, pitting, etc. Electroless coating can be a good alternative to overcome these issues. These coatings can create novel nickel-based composite materials, of which Ni-P-Cu is the most common when the application demands the property of heat conduction. These coatings also provide great corrosion resistance. As our objective is the application of these composite coatings on heat exchangers, both corrosion and heat transfer properties have been demonstrated respectively in this study. The analysis has chosen electroless ENPC-coated mild steel at various concentrations of copper ranging from 0.2 g/l to 1.2 g/l. The surface morphology and elemental analysis have been explained using FESEM and EDX analysis. The material phase transformation has been observed using an XRD plot. The microhardness of the sample before and after the heat transfer study has been analysed and compared. The Tafel curve of the heated sample showed the increase of corrosion resistivity within the temperature range of 100°C to 400°C for an optimised coated sample ENPC-1, (i.e., electroless nickel phosphorous copper coating with copper concentration 1 g/l). A spray cooling setup built in house has been used to analyse the heat transfer mechanism. The cooling rate obtained for the ENPC-1 sample is around 25.2% more than in the previous studies on uncoated samples using base fluid (water).