Elevated temperature tribological behavior of NiMoAl-Ag-WS2-hBN coatings deposited by cold spray

Abstract

The current research work evaluates the tribological performance of cold sprayed coatings, namely NiMoAl-10 wt % Ag (NA), NiMoAl-10 wt % WS2 (NW), NiMoAl-5 wt. % Ag-5 wt. % WS2 (NAW), and NiMoAl-5 wt. % Ag-5 wt. % WS2-5 wt. % h-BN (NAWB) in extended working regime of temperature from room temperature RT (25 °C) to 800 °C. As a counter face material alumina ball of diameter 6.2 mm was chosen. The hardness of the said coating (NA) was recorded as 390 HV0.5. The addition of WS2 in NiMoAl matrix increases the hardness of the coating (NW) to 445 HV0.5. For the designated coating (NAW) hardness decreased to 410 HV0.5, due to combined addition of silver and WS2. The addition of 5 wt % h-BN in the designated coating (NAWB) further reduced the hardness of the coating and attain the hardness value to 364 HV0.5. The addition of solid lubricants (Ag, WS2 and h-BN) significantly reduced the coefficient of friction (COF) and wear rate as a result the formulated coating (NAWB) has demonstrated the lowest COF and wear rate across all testing temperatures. The COF value decreased from 0.3 at RT to 0.14 at 800 °C showing continuous decline as temperature increased. The superior tribological properties shown by the coating (NAWB) has been credited to addition of h-BN in the coating along with tribo induced various oxides (NiMoO4, NiO, MoO3, and WO3), silver molybdates creation through tribo-chemical reactions and their synergistic action at elevated temperatures. These compounds continuously protect the mating surfaces and inhibit the direct contact, enhance the tribological characteristics by forming protective tribo-layers during sliding. This suggests that such composite coatings are promising for applications requiring high-temperature wear resistance and low friction. © 2025 Elsevier B.V.