Effects of pH values in electroless Ni plating on mild steel with TiN coating

Abstract

TiN films are prepared by reactive r.f. magnetron sputtering on mild steel substrates. An electroless Ni-P plating is introduced as an interlayer in the surface modification of a TiN coating. A hypophosphite-based bath is employed for electroless Ni-P deposits. The electroless Ni-P deposits crystallize during r.f. sputtering, owing to the elevated sputtering temperature, and thus a TiN/Ni3P/Fe coating assembly is formed. The pH value of the bath affects the phosphorus content of the electroless Ni-P deposits, and the phosphorus contents vary from 6.7 wt.% to 11 wt.% as the pH value is changed from 5.5 to 4.0. The as-plated structure is amorphous for the range of 7.6 wt.% to 11 wt.% phosphorus, and is microcrystalline for the case of 6.7 wt.% phosphorus. The employment of an electroless Ni-P deposit results in an increase in surface microhardness and adhesion strength. In addition, an appropriate thickness of electroless Ni-P without a substrate effects is evaluated. © 1993.