Mechanical and wear characterization of electroless nickel mono and bilayers and high boron-mid phosphorus electroless nickel duplex coatings

Abstract

Abstract The mechanical and wear properties of electroless nickel monolayer, bilayers and duplex NiP/NiB coatings were investigated in the as deposited state. Bilayers and duplex coatings, constituted of two layer of 10 μm each, were prepared according to four distinct configurations (NiB/NiP; NiP/NiB; NiB/NiB and NiP/NiP). Single layer coatings from each electroless nickel bath with a thickness of 20 μm were also synthesized and analyzed in this work: mid phosphorous NiP (nickel-phosphorus) and high boron NiB (nickel-boron). The microhardness, roughness and wear resistance of electroless nickel duplex coatings were compared with electroless NiP and NiB coatings of similar thickness. The hardness characteristics of duplex coatings are really influenced by the high hardness of NiB coatings: the hardness of pure NiP coatings was 550 HV while the presence of NiB coating as underlayer allowed to reach 738 HV. SEM observations of the cross-sections of the nickel duplex coatings also reveal that coatings are uniform with proper compatibility between layers.