Influence of Added Elements on ACD Electroless NiP

Addition of other metals can greatly influence the Autocatalytic Chemical Deposition ACD NiP plating process. The most important effects are related to possible codeposition, obtaining ternary or quaternary alloys, or stabilization of the bath. Minor, but not less important, effects regard deposit aspect and structure, phosphorus content, corrosion and wear resistance, stability of the deposits with respect to thermal treatments. A general interpretation of the influence of the added elements on the process and the deposit properties is proposed. The behaviour of the added elements is generally anti-correlated with their behaviour in electrodeposition. Elements giving anomalous alloy electrodeposition, such as Zn, Co and Fe behave normally in electroless baths; elements electrodeposited by induction, such as W and Mo, have important effects on the electroless process: they decrease the P content and the deposition rate, while increasing the corrosion resistance. Some of the metal stabilizers, such as Pb, Tl, Hg, Cd, Sb, Bi and Te, can have also a brightening effect on NiP deposits. This is the case of Cd, Sb, Bi and Te and this effect can be related to their interaction with adsorbed hydrogen, which is stabilized by these additives.