MICROSTRUCTURES AND CRYSTALLIZATION OF ELECTROLESS NI-P DEPOSITS

A study has been made of microstructures and crystallization of the electroless Ni-P deposits containing 11.3 to 23.0 at% P obtained from acidic nickel sulphate baths with sodium hypophosphite as a reducing agent by means of differential scanning calorimetry, X-ray diffractometry and hot stage transmission electron microscopy. The deposits containing low phosphorus content of 11.3 at% could be represented as an fcc Ni-P solid solution of 5 to 10 nm microcrystallites, whereas the deposits containing high phosphorus content were amorphous. The crystallization process of amorphous Ni-P solution involved more than one intermediate phases; precrystallized nickel or off-stoichiometric Ni3(P, Ni) or Ni5(P, Ni)2 phase in which some phosphorus sites are replaced by nickel atoms. The final equilibrium phases were bct Ni3P and fcc nickel crystals regardless of phosphorus content. The amorphous phase containing 20 to 22 at% phosphorus was the most stable among the amorphous Ni-P alloys. © 1990 Chapman and Hall Ltd.