Microstructural, Mechanical and Tribological Properties of Electroless Duplex NiP/NiB Coatings on Steel

摘要

Electroless nickel coatings present interesting mechanical, tribological and corrosion resistance properties. However, the two main kinds of electroless nickel coatings - Nickel-phosphorous (ENP) and nickel-boron (ENB) - are each more popular for some applications (corrosion resistance and mechanical applications respectively).To assess the potential of cumulating the best features of each kind of coating, duplex electroless nickel coatings are investigated. The coatings used in the study were synthesized on mild steel substrates from a commercial bath in the case of nickel-phosphorous and from a lab-developed composition in the case of nickel-boron(with sodium borohydride as reducing agent and lead salts as stabilizer).Single coatings of each electroless nickel composition with a thickness of 20 mμ were synthesized and compared with duplex layers (10 + 10 urn) made as follow: ENP/ENB; ENB/ENP, ENP/ENP and ENB/ENB.The morphology of all coatings was observed, their hardness, roughness and Taber abrasion index were measured and their resistance to scratch test was assessed. Systems with ENB on the top showed better abrasive wear performance, due to the higher hardness of nickel-boron and despite the higher roughness of ENB. The best resistance to scratch testing was obtained with single and double NiB coatings.