Effect of Heat Treatment on Tribological Behavior of Electroless Ni-B-Mo Coatings at Different Operating Temperatures

The present work aims to characterize the tribological behavior of electroless Ni-B-Mo coatings in their as-plated and heat treated conditions deposited on AISI 1040 steel. Heat treatment temperatures considered are 350 °C, 400 °C and 450 °C. Friction and wear tests are carried out at room (25 °C) and elevated temperatures of 100 °C, 300 °C and 500 °C. The as-deposited Ni-B-Mo coatings show a high wear rate compared to the heat treated ones at room as well as elevated temperatures. The wear rate of the heat treated coatings at high temperatures does not show a significant variation which is indicative of their high thermal stability. A similar result is also observed for the coefficient of friction of the heat treated Ni-B-Mo coatings. Analysis of worn specimens at 500 °C indicates the formation of protective tribo-oxide layers and occurrence of microstructural changes due to the in-situ heat treatment effect resulting from the high operating temperatures. The wear debris also significantly affects the tribological mechanisms of the coatings at high operating temperatures.