Investigation of the physical and mechanical properties of Ni–P and Ni–P–PTFE nanocomposite coatings deposited on aluminum alloy 7023

Abstract

In this study, various properties of Ni–P and Ni–P–PTFE coating fabricated by electroless process were investigated. These coatings were applied on aircraft-grade aluminum samples. The results showed that the addition of nano-PTFE particles decreases coating rate from 7.1 µm/h to 6.1 µm/h and hardness from 510 HV to 200 HV. Also by increasing the pH value, coating rate increases from 1 µm/h to 7 µm/h. Increasing the solution temperature from 75 ℃ to 90 ℃ also increases the hardness of coating from 125 HV to 210 HV. The results showed that the heat treatment at 300 ℃ for 4 h increases the hardness up to 375 HV due to formation of Ni₃P hard phase in Ni–P–PTFE coating. Addition of PTFE particles have improved tribological properties due to its lubricating effects and simultaneously, have reduced corrosion resistance compared to Ni–P coatings, so that the corrosion current for Al, Ni–P, and Ni–P–PTFE coatings is −880, −550, and −770 μA/cm², respectively.