Tribological behavior of autocatalytic Ni-P based duplex coatings

Abstract

The present research evaluates the tribological performance of different Ni-P based duplex autocatalytic coatings (electroless coatings). The study investigates coatings including Ni-P/Ni-W-P, Ni-P/Ni-Mo-P, and Ni-P/Ni-Cu-P, examining various factors such as heat treatment conditions, sample composition, and their influence on the coatings’ performance. The phase structure of the coatings is influenced by heat treatment parameters viz. temperature and duration as well as phosphorus content. Notably, at temperatures above 400 °C, all duplex coatings form a robust nickel phosphide phase, enhancing hardness and wear resistance which is almost double of that in as-deposited state in some cases. When subjected to a temperature of 400 °C for duration of 1 h, the Ni-P/Ni-W-P coating displays the highest microhardness (1440 HV0.1) and the lowest wear rate (10.62 × 10−5. mm3. N−1. m−1) among all the duplex coatings. In all three duplex systems, the wear typically involves a combination of abrasive and adhesive mechanisms. Among the as-deposited coatings, the Ni-P/Ni-Cu-P demonstrates higher corrosion potential (E corr −302 mV) and lower corrosion current (i corr 1.83 × 10−5 mA cm−2) which imply superior corrosion resistance compared to the other duplex coatings. In the heat-treated state, the Ni-P/Ni-Mo-P duplex coating generally exhibits better corrosion resistance when compared to the other two types of duplex coatings.