Thermal Stability, Hardness, and Corrosion Behavior of the Nickel–Ruthenium–Phosphorus Sputtering Coatings

• Main Authors: Yu-Cheng Hsiao, Fan-Bean Wu
• Format: Article
• Language: English
• Published: MDPI AG 2020-08-01
• Series: Coatings
• Subjects: Ni–Ru–P; sputtering; annealing; corrosion
• Online Access: https://www.mdpi.com/2079-6412/10/8/786

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 Ni_xP_y 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 <i>E</i>_corr 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 <i>E</i>_corr 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 Ni<i>_x</i>P<i>_y</i> crystallized phases during annealing is responsible for the degeneration of corrosion resistance.