Evaluation of tribological characteristics for HVOF deposited Ni based self-lubricating coatings with different h-BN composition

Abstract

The tribological behaviour of High Velocity Oxygen Fuel (HVOF) thermal spray deposited coatings, namely Ni-Al-Ag-MoS2 (NAMB0), Ni-Al-Ag-MoS2–5 wt. % h-BN (NAMB5), Ni-Al-Ag-MoS2–7.5 wt% h-BN (NAMB7.5) and Ni-Al-Ag-MoS2–10 wt% h-BN (NAMB10), on Inconel 718 as substrate material were assessed against an alumina ball as a counterface. The tests were performed using a rotary tribometer under “ball on disc configuration” at various testing loads of 5, 10, 15, 20 N and a fixed sliding speed of 0.5 m/s at room temperature (RT) of 25 °C. The weight percent of MoS2 and Ag as a solid lubricant were kept constant whereas h-BN wt% was varied in the coated samples i.e. 0, 5, 7.5 and 10 wt. According to test results, as the load increases from 5 to 15 N, both coefficient of friction (COF) and wear rate exhibit a decreasing trend in nature, thereafter, by increasing the load up to 20 N, the reverse action is evident. However, the coating having 7.5 wt% h-BN along with MoS2 and Ag has revealed the best tribological behaviour under the investigational parameters. The observed behaviour has been attributed to the synergistic effect of Ag, MoS2 and h-BN and optimum content of h-BN in NAMB7.5 coatings enhances the tribological performance to its apex. © 2023 Elsevier B.V.