Mechanical properties of heat-treated duplex electroless nickel coatings

Abstract

Electroless nickel coatings present complementary properties: coatings formed using hypophosphite present usually better corrosion resistance while those made with borohydride present better mechanical and wear properties. Duplex coatings, combining both kinds of deposits, are designed to combine features of both nickel-phosphorus (ENP) and nickel-boron (ENB) coatings. In this study, monolayer and bilayer coatings were synthesised on mild steel substrates, in various combinations of ENP and ENB, with a total thickness of 20 µm and heat treated (400°C -1 h) under non-reactive atmosphere (95% Ar-5% H 2 ) to enhance their mechanical properties. The morphology, roughness, hardness, abrasive wear resistance and scratch behaviour of the coatings were investigated. Samples with ENP as the top layer showed a higher roughness than samples with ENB as the external layer. However, samples with ENB as the top layer provided better wear resistance, even if they presented a lower combined hardness. ENB monolayer showed the best resistance to scratch testing.

Replacement of Lead stabilizer in electroless Nickel-Boron baths: Synthesis and characterization of coatings from bismuth stabilized bath

“…From a morphological point of view, NiB-Bi coatings present morphologic variations in the film between the outer part and the inner part. NiB-Pb presents a completely columnar structure [22,36,37]. As explained before, this difference is caused by the high redox potential of Bi +3 compared with Pb 2+ .…”

Recent advances in electroless nickel‑boron coatings

“…The chemistry of coatings is not only influenced by the reducing agent and operating conditions but also by the type of stabilizer. DMABreduced coating usually contains less boron than those from borohydride-based baths, which can contain up to 8 wt% boron [145]. Experiments carried out on NaBH 4 -reduced baths have shown that the percentage of boron increases with the amount of reducing agent in the bath and with temperature [145,146].…”

“…DMABreduced coating usually contains less boron than those from borohydride-based baths, which can contain up to 8 wt% boron [145]. Experiments carried out on NaBH 4 -reduced baths have shown that the percentage of boron increases with the amount of reducing agent in the bath and with temperature [145,146]. The most frequent chemistry of EN-B deposits is 5 to 6 wt% B with or without incorporated stabilizing agent [17].…”

Optimizing Electroless Plating of Ni–Mo–P Coatings Toward Functional Ceramics

“…The ED process of Ni coatings has been studied in depth lately due to their mechanical properties or resistance to corrosion, wear and friction [24][25][26] and their electrocatalytic activity [27]. Overall, ED of Ni could lead to Ni-X-P or Ni-X-B coatings, where X could be an alloying metal or a composite particle (such as W, Cu, Zn, Co, CNTs), P is phosphorus and B is boron [14,25].…”