Influence of Ni ¹³⁺ ions irradiation on the microstructure, mechanical and tribological properties of Mo-S-Ti composite films

In this study high energy nickel ions bombardment was used to simulate the neutron irradiation on Mo-S-Ti composite films prepared by magnetron sputtering, and the influence of heavy ion bombardment on the microstructure, mechanical and tribological properties of film was investigated as function of Ni ions incident fluence up to 11.8 × 10 ¹⁴ Ni ¹³⁺ /cm ² . The structural evolution of bulk film after irradiation was investigated using transmission electron microscopy (TEM). TEM results indicate that the mostly defects of films after Ni ¹³⁺ irradiation are the amorphization of the MoS ₂ crystals and the damage peak mainly happened inside 1.2 μm–1.6 μm deep in films. The nano-indentation tests show an obvious irradiation hardening of irradiated films. Particularly, the hardness of Mo-S-Ti films under irradiation with ion fluence of 5.88 × 10 ¹⁴ Ni ¹³⁺ /cm ² reaches up to 12.74 GPa, and corresponding elastic recovery ratio (d _elastic /d _max ) increases up to 65%. Benefiting from the enhanced mechanical properties and unchanged S/Mo of irradiated composite film, the highly distorted MoS ₂ phases caused by ion irradiation exhibits a structural transformation under the induction of a rotating shear stress, from disordering to finely-aligned (002) basal planes in parallel to the shearing direction, which results in low friction coefficient in vacuum sliding conditions.