Friction and wear of Ni alloy-Ag-Ni doped hBN self-lubricating composites from room temperature to 800 °C

Abstract The current investigation explores the potential of Ni-doped hBN (hBN-O-Ni) as a solid lubricant in conjunction with Ag in improving the tribological performance of Ni alloy-Ag-hBN composites containing a fixed amount of silver (10 wt%) and different amounts (2, 4, 6, and 8 wt%) of hBN from room temperature to 800 °C by carrying out tests under a fixed load of 5 N and speed of 0.5 m/s using a ball-on-disk tribometer. The study also intends to determine the occurrence of any synergistic action between Ag and a hybrid nanomaterial (Ni-doped hBN) in achieving low friction and low wear properties over an extended range of temperatures. The results indicate that the composite having 4 wt% hBN exhibited the lowest wear-rate among all the materials, whereas the composite having 8 wt% hBN displayed the lowest coefficient of friction at all the temperatures under the condition of load and sliding speed used in the present study. The composite having 8 wt% hBN attained the lowest coefficient of friction (∼0.18) at 800 °C due to synergistic action between silver molybdates and hBN. At low temperatures, Ag and hBN provided lubrication, whereas at high temperatures lubricious oxides (NiO, NiMoO4, and MoO3), silver molybdates (Ag2MoO4, Ag2Mo2O7), and hBN contributed to lowering the coefficient of friction as well as wear-rate.