Thermal stability, hardness, and corrosion behavior of the nickel-ruthenium-phosphorus sputtering coatings

Abstract

Nickel-ruthenium-phosphorus, Ni-Ru-P, alloy coatings were fabricated by magnetron dual-gun co-sputtering from Ni-P alloy and Ru source targets. The composition variation and related microstructure evolution of the coatings were manipulated by the input power modulation. The as-prepared Ni-Ru-P alloy coatings with a Ru content less than 12.2 at. % are amorphous/nanocrystalline, while that with a high Ru content of 52.7 at. % shows a feature of crystallized Ni, Ru, and Ru2P mixed phases in the as-deposited state. The crystallized phases for high Ru content Ni-Ru-P coatings are stable against annealing process up to 600 °C. By contrast, the amorphous/nanocrystalline Ni-Ru-P thin films withstand a heat-treated temperature up to 475 °C and then transform into Ni(Ru) and NixPy crystallized phases at an annealing temperature over 500 °C. The surface hardness of the Ni-Ru-P films ranges from 7.2 to 12.1 GPa and increases with the Ru content and the annealing temperatures. A highest surface hardness is found for the 550 °C annealed Ni-Ru-P with a high Ru content of 52.7 at. %. The Ecorr values of the heat-treated amorphous/nanocrystalline Ni-Ru-P coatings become more negative, while with a high Ru content over 27.3 at. % the Ni-Ru-P films show more negative Ecorr values after annealing process. The pitting corrosion feature is observed for the amorphous/nanocrystalline Ni-Ru-P coatings when tested in a 3.5M NaCl solution. Severer pitting corrosion is found for the 550 °C annealed Ni-Ru-P coatings. The development of Ni(Ru) and NixPy crystallized phases during annealing is responsible for the degeneration of corrosion resistance.