Microstructure evolution and erosion-corrosion resistance of amorphous Ni-P coatings

Amorphous Ni-P coatings with 7.8 wt% P were electrodeposited successfully from an electrolytic bath containing 15 g/L H3PO3. Its microstructure evolution by heat treatment and erosion-corrosion resistance are investigated in this paper. From room temperature to 500 A degrees C, there were three exothermic crystalline phases of Ni5P2, Ni3P and Ni precipitated from the amorphous base. The microstructure evolution of the amorphous Ni-P deposits follows the sequence of amorphous, amorphous-noncrystalline, (Ni5P2 + Ni3P), then (Ni5P2 + Ni3P + Ni) with increasing heat treatment temperature. The mass loss rate of amorphous Ni-P coatings is approximately 14 mg/h and the synergism of erosion-corrosion was larger than half of the total mass loss at an impingement velocity of 8.37 m/s under saline-sand slurry. The erosion-corrosion resistance of amorphous Ni-P coatings can be enhanced obviously by heat treatment because of the elevated hardness and corrosion resistance.