High temperature tribological properties of Ni-based self-lubricating coatings deposited by atmospheric plasma spray

Abstract Friction and wear characteristics of atmospheric plasma sprayed Ni-Al–Ag–MoS 2 , Ni-Al-Ag-MoS 2 -5 wt% hBN and Ni-Al-Ag-MoS 2 -10 wt% hBN coatings were examined against alumina ball at a constant load of 5 N and sliding velocity of 0.3 m/s from room temperature (RT) to 800 °C using a high temperature tribometer. The hardness of coatings was found to decrease from 182 HV 0.2 to 164 HV 0.2 with addition of 5 wt% hBN which further decreased to 155 HV 0.2 for 10 wt% hBN. Both the friction coefficient and the wear rate were found to decrease with increasing temperature from RT to 800 °C for all the coatings. However, the coating containing 5 wt% hBN showed a consistently lower coefficient friction and wear rate in comparison to other coatings. The coefficient of friction for Ni-Al-Ag-MoS 2 -5 wt% hBN coating decreased from 0.5 to 0.23 with an increase in temperature from RT to 800 °C. The observed behavior has been attributed to the presence of NiO, AgMo x O y in the tribo-layer and the synergistic action of hBN which helped Ag and MoS 2 in enhancing the friction and wear performance of coatings.