Electroless deposition of Ni–P and Ni–P–Re alloys from acidic hypophosphite baths

Ni–P and Ni–P–Re coatings with various concentrations of P and Re were obtained on copper substrate by the electroless deposition from succinate baths. The influence of certain bath parameters on the alloys composition and the deposition rate is presented, followed by the relation between these process parameters as well as the rhenium addition on the surface morphology, microstructure, phase composition and thermal stability of the deposited films. The conditions for the formation of uniform, smooth and compact alloy films on copper substrate were defined. On the basis of X-ray diffraction analysis it can be stated that the alloy containing less than 5.5 wt.% of phosphorus exhibits fully crystalline microstructure for both studied cases: Ni–P and Ni–P–Re alloys. Differential scanning calorimetry analysis performed for the Ni-based alloy layers with and without rhenium additive and the same level of phosphorus are provided, proving, that the addition of rhenium to the Ni–P coatings results in the increase of the crystallization temperature. The increase of the crystallization temperature from 411 °C to 434 °C was noted for NiP5.0 alloy, where the addition of Re was only of 3.7 wt.%.