Effect of annealing on magnetic properties and microstructure of electroless nickel-copper-phosphorus alloy deposits

Abstract

The relationship between magnetic properties and microstructure of the as-deposited and heat-treated Ni-Cu-P alloy deposits has been studied by means of vibrating sample magnetometry, differential scanning calorimetry. X-ray diffractometry and hot-stage transmission electron microscopy. The Ni-Cu-P deposits consist of low-P Ni-Cu solid solution crystallites and high-P-low-Ni-Cu amorphous phase. When the deposits are annealed at elevated temperatures, the Ni-Cu crystallites grow rejecting P from themselves and absorbing Cu from the neighbouring amorphous phase, while the P-rich amorphous phase transforms into Ni₅P₂ phase or into Ni₅P₂ and Ni₃P phases. The metastable Ni₅P₂ phase finally transforms into the stable Ni₃P phase. The non-magnetism observed in Ni-Cu-P deposits having a copper content above 28% in both as-deposited and annealed states, is attributed to their Cu-rich Ni-Cu solid solution crystallites. Nickel phosphides which crystallize from the amorphous phase existing mixed with the Ni-Cu crystallites in the as-deposited state, do not affect the saturated magnetic moment of the deposits.