Abstract
The ternary Ni–P–Al alloy coatings were fabricated by RF magnetron sputtering technique with dual targets of Ni–P/Cu as well as an additional aluminum metal. Electroplating Ni–P process was introduced to obtain the NiP compound target with various phosphorous contents after modification of the processing parameters. Thermal analysis revealed that the introduction of Al in the Ni-P coating by co-deposition retarded the Ni and Ni3P precipitation and retained the strengthening effect at elevated temperature. Microstructure evolution indicated that all coatings in the as-deposited state exhibited amorphous structure. The precipitation of Ni and Ni3P accompanied with Al dissolved into Ni matrix were the final product of the phase transformation in Ni-P-Al coatings after heat treatment. It was revealed that hardness can be engineered by the controlling of composition in the Ni-P-Al coatings. After annealing, the coating was strengthened by the precipitation of Ni-P compounds and dissolved Al in the crystallized Ni. Through quantitative analysis, the effect of strengthening in ternary Ni-P-Al coatings can be clearly demonstrated.