Compo­sition, structure and properties of electroless deposited nickel – phosphorus – copper coatings

The nickel – phosphorus – copper functional coating was deposited on aluminum alloys substrate by chemical deposition method from malonate­glycinate nickel plating solution. The chemical and phase coatings composition was studied by X­ray fluorescence and X­ray phase analyze. Thermally stimulated phase transitions in deposited Ni – P – Cu coating were detected by differential scanning calorimetry method. The annealing at 250 and 400 °С was shown to lead to the changes in coating structure involving the transition from amorphous to amorphous­crystalline at 250 °С and to crystalline at 400 °С with Ni and Ni3P1 –  δ phases forming. Changes in the structure of Ni–P coating results in the increase of microhardness by 1.6–1.7 times and wear resistance by 3– 4 times. Annealing at 400 °С led to decreasing of corrosion stability of the coatings in 3.5 % sodium chloride solution. The optimum physical, mechanical and protective properties has the attained in the case of Ni – P – Cu coating annealed at 250 °C.