Abstract
Ternary Ni-P-Al coatings were fabricated by the dual-gun rf magnetron sputtering technique. The as-deposited Ni-P-Al coatings exhibited a major Ni nanocrystalline phase (with a (111) texture) with Al and P co-deposited. After 400 °C heat treatment, various Ni x P y compounds, including Ni 12 P 5 , Ni 5 P 2 , and Ni 3 P, formed within the recrystallized Ni matrix. Accordingly, the hardness of the coating increased to 10 GPa due to the Ni x P y precipitation. For heat treatment temperatures higher than 450 °C, Ni p Al q hard phases were observed in the ternary Ni-P-Al coating. A further increase in coating hardness from 10 to 12 GPa was revealed. The hardening of the annealed Ni-P-Al coatings was attributed to precipitation of Ni-P and Ni-Al compounds formed around 400 and 500 °C, respectively. A two-stage hardening in Ni-P-Al coating by Ni x P y and Ni p Al q precipitation through heat treatment was then demonstrated. Through surface analysis, the increase in surface roughness for the Ni-P-Al coating due to the formation of Ni x P y and Ni p Al q compounds was revealed. © 2005 Elsevier B.V. All rights reserved.