Electroless deposited ternary alloys: third element chemical state, localisation and influence on the properties. A short review

Electroless deposited ternary alloys have been reviewed in relation to the chemical state of the third element, its localisation and the possible influence of these on alloy properties. Three types of electroless Ni-W-P, Co-W-P and Ni-Zn-P coatings have been investigated. Low P deposits are nanocrystalline and those with higher P content are amorphous. X-ray diffraction has proved the localisation of W, Zn and P along the nanograin boundaries. The localisation of Zn along with P has also been confirmed by transmission electron microscopy combined with energy dispersion spectroscopy. Analysing the X-ray photoelectron spectroscopy (XPS) spectra it has been found that within the coatings W is in elemental form, whereas Zn is partially oxidised. XPS data also show that the crystalline structure promotes the surface oxidation to a higher extent than in the case of amorphous structure. The wear resistance of nanocrystalline Ni-W-P coatings is much higher. A lower corrosion resistance of amorphous Ni-W-P coatings has been found by weight-loss method during long-term immersion in 5% NaCl. It is illustrated that in addition to the composition and structure, the properties depend on the distribution and chemical state of the alloy components.