Adaptive tribological performance of porous ticn-mos2 composite coatings in response to fluctuating humidity conditions

Abstract

To improve the friction and wear performance of coatings in aerospace engineering under wet and dry alternating conditions, the porous hard TiCN coating was prepared by a combination of multi-arc ion plating and oblique angle deposition. The study found that when the titanium target current was reduced from 80 A to 60 A, the pore size of the porous TiCN coating increased from 0.30 μm to 0.93 μm. In comparison to the low hardness of stainless steel substrate of 3.4 GPa, the hardness of TiCN coatings with pore sizes of 0.93 and 0.30 μm rose to 10 and 22 GPa, respectively. The existence of pores can effectively improve the hydrophilicity of the coatings. However, as the pore size increased, the anti-wear lifetime of the coatings were also decrease. This process was followed by ultrasonication and hydrogen reduction of (NH4)2MoS4 to infuse MoS2 directly into the pores to fabricate the TiCN-MoS2 composite coatings. The findings revealed MoS2 atomic sheets are randomly embedded in the pores of the TiCN coating. In a stable humidity environment, as the relative humidity increased, the friction coefficient of the TiCN-MoS2 porous composite coating increased and the anti-wear lifetime decreased. In addition, the anti-wear lifetime of the TiCN-MoS2 porous composite coating at 20 % relative humidity environment is 128,322 laps, which exceeded the 38,099 laps of the dense TiCN-MoS2 composite coating. This proved that the porous composite coating had better anti-wear lifetime due to the continuous release of MoS2 in the pores under low humidity conditions. The tribological behavior of the porous composite coatings was systematically investigated under alternating humidity conditions, with a comparison against the dense TiCN-MoS2 composite coatings. The porous composite coatings possessed better self-adaptation under alternating humidity conditions, with coefficients of friction of 0.05 and 0.15 at 10 % and 70 % RH air, respectively. A detailed discussion was conducted on the relationship between tribofilm composition and tribological properties under different humidity environments.