Tribological behavior of autocatalytic Ni–P–B coatings at elevated temperatures

Abstract

Ni–P–B coatings are produced directly on surface of carbon steel (AISI 1040) using electroless plating technique. The effects of temperature on the friction and wear behavior of Ni–P–B alloy coatings have been investigated. Tribological tests are conducted at four temperatures (30, 100, 300 and 500\xa0°C) under constant load and sliding speed in a pin-on-disk apparatus. Results show that Ni–P–B coatings sustain the elevated temperatures with minimal effect on friction and wear performances. Ni–P–B coating is found to exhibit the maximum hardness among the binary Ni–P and Ni–B coatings with as-deposited hardness reaching around 700HV. Heat treatment increases the hardness as well as wear resistance by precipitation of boride and phosphide phases of nickel. Room temperature test shows mostly adhesive wear pattern but finally, it leads to a mixture of abrasive–adhesive wear mechanism. Friction and wear of Ni–P–B is overall governed by the formation of oxidative layer, mechanically mixed layer with iron (from ferrous counter face), wear mechanism, phase transformation and changes in microstructure during elevated wear test. Phase transformation and corresponding micro-structural changes occurring during elevated test duration help in providing better wear resistance to the coating.