Structure, hardness and adhesion in electroless nickel interlayer modified TiN coating on mild steel

[[abstract]]TiN films have been prepared by reactive rf magnetron sputtering on mild steel substrates, and electroless Ni-P plating has been introduced as an interlayer. A hypophosphite-based bath has been used in this study to produce electroless Ni-P coatings. The electroless Ni-P deposits crystallize during rf sputtering due to the high sputtering temperature and a TiN/Ni3P/Fe coating assembly is formed. The pH value of the bath will affect the phosphorus content of the electroless Ni-P deposits, and the phosphorus content changes from 6.7 wt.% to 11 wt.% for pH 5.5 to pH 4.0. It is observed that the Ar/N2 flux ratio has a significant influence on the phase and structure of the deposited TiN film. The deposition rate increases as the nitrogen content is decreased. Pure TiN coatings are obtained for the Ar/N2 flux ratio range from 90/10 to 70/30. Unreacted Ti is found at an Ar/N2 ratio of 95/5 and 60/40 due to the incomplete reaction to form TiN. The employment of an electroless Ni-P deposit results in an increase in the surface microhardness and the adhesion strength. The surface hardness values were as high as 2266 HK1, close to the hardness of bulk TiN with the formation of an Ni3P interlayer modified TiN coating.[[fileno]]2020323010144[[department]]材料科學工程學