Effect of bias voltage on structure, mechanical properties and tribological performance (against simulated lunar dust) of NiCrMoAl thin films deposited by DC magnetron sputtering

As lunar exploration missions progress, the wear failure of moving parts due to lunar dust has become a critical concern. This study focuses on the development of NiCrMoAl thin films deposited on 304 stainless steel substrates via magnetron sputtering, investigating the impact of bias voltages (-100 V, -300 V, -500 V) on their structure and tribological properties in simulated lunar dust environments. The results indicate that the hardness of the base material is 8.7 GPa. When the bias voltage is -100 V, the film surface is smooth with a nano-hardness of 20.6 GPa. Increasing the bias voltage to -300 V, enhances nano-hardness to 27.6 GPa due to decreased defect density and denser structure from ion bombardment. However, at -500 V, stress accumulation leads to micro-cracks, reducing hardness to 19 GPa. The results showed that the friction coefficients of the matrix and the samples prepared under three different bias voltages were stable within the range of 0.4 – 0.7. Among them, the friction coefficients were more stable when the bias voltages were -100 V and -300 V. When the bias voltage was -300 V, the wear rate of the sample was the lowest, reaching 0.33 × 10 - 4 mm 3 /(N·m). In tests with simulated lunar dust at varying concentrations, the -300 V samples displayed excellent tribological properties with a friction coefficient fixed between 0.5 – 0.6 and a wear rate maintained below 0.6 × 10 - 4 mm 3 /(N·m) under different lunar dust concentrations.