Tribological properties of MoS2/C coatings with different carbon contents (44.7–84.3 at.%) deposited by magnetron sputtering were systematically investigated under atmospheric environment. During tribological tests, the coating with the least MoS2 content exhibited the lowest friction coefficient and wear rate, while coating with the most MoS2 showed the worst performance. To understand friction and wear mechanism, multiple analytical tools such as SEM, EDS, Raman, XPS and TEM were applied to investigate the composition and structure. TEM and SEM characteristics proved that the tribofilm with multilayered structure was formed on the tribopair. The C-rich layer adhered to the tribopair and the top layer was well-ordered MoS2 tribofilm, and the dominated amorphous MoS2 was found between the two layers. It suggested that the shear plane was mainly made of well-ordered MoS2 transfer film, while carbon improved the mechanical properties of the coatings, served as a lubricant and also inhibited the oxidation of MoS2.

•The nanocomposite V–Al–C coatings were deposited.•Structure evolution of V–Al–C coatings upon annealing temperature was studied.•The pure V2AlC MAX phase was obtained after annealing beyond 700 °C.•The correlation between the structure and mechanical properties was established.•Toughness and tribological properties were optimized with structure evolution.V2AlC belongs to a family of ternary nano-laminate alloys known as the MAX phases, which exhibit a unique combination of metallic and ceramic properties. In this work V–Al–C coatings with deposited (V,Al)2C nano-crystallines and amorphous phase were magnetron sputtered from V2AlC compound target. The subsequent vacuum annealing for 1 h was carried out at 600 °C, 700 °C and 800 °C, respectively. The crystallization of V2AlC MAX phase was detected by annealing at 600 °C. Meanwhile, a small amount of amorphous carbon phase appeared. Further increasing annealing temperature to 700 °C led to a complete transformation from amorphous V–Al–C phase to V2AlC phase, as well as a significant increase in the amorphous carbon content. It was noticed that the crystallinity of V2AlC phase was significantly enhanced and amorphous carbon was almost disappeared after annealing at 800 °C. The coating toughness became better with the increase in the content of V2AlC MAX phase. The optimized mechanical and tribological properties of the annealed V–Al–C coatings were further discussed in terms of the microstructure evolution.

TiN coatings were deposited using a hybrid home-made high power impulse magnetron sputtering (HIPIMS) technique at room temperature. The effects of substrate negative bias voltage on the deposition rate, composition, crystal structure, surface morphology, microstructure and mechanical properties were investigated. The results revealed that with the increase in bias voltage from −50 to −400 V, TiN coatings exhibited a trend of densification and the crystal structure gradually evolved from (111) orientation to (200) orientation. The growth rate decreased from about 12.2 nm to 7.8 nm per minute with the coating densification. When the bias voltage was −300 V, the minimum surface roughness value of 10.1 nm was obtained, and the hardness and Young's modulus of TiN coatings reached the maximum value of 17.4 GPa and 263.8 GPa, respectively. Meanwhile, the highest adhesion of 59 N was obtained between coating and substrate.

Due to the excellent corrosion resistance and high irradiation damage resistance, Ti2AlC MAX phase is considered as a candidate for applications as corrosion resistant and irradiation resistant protective coating. MAX phase coatings can be fabricated through firstly depositing a coating containing the three elements M, A, and X close to stoichiometry of the MAX phases using physical vapor deposition, followed by heat treatment in vacuum. In this work, Ti–Al–C coating was prepared on austenitic stainless steels by reactive DC magnetron sputtering with a compound Ti50Al50 target, and CH4 used as the reactive gas. It was found that the as-deposited coating is mainly composed of Ti3AlC antiperovskite phase with supersaturated solid solution of Al. Additionally, the ratio of Ti/Al remained the same as that of the target composition. Nevertheless, a thicker thermally grown Ti2AlC MAX phase coating was obtained after being annealed at 800 °C in vacuum for 1 h. Meanwhile, the ratio of Ti/Al became close to stoichiometry of Ti2AlC MAX phases. It can be understood that owing to the higher activity of Al, it diffused quickly into the substrate during annealing, and then more stable Ti2AlC MAX phases transformed from the Ti3AlC antiperovskite phase.

•The oxidation of Ti2AlC coating at 750 °C in air and pure water vapor was studied.•Ti2AlC coating improves the oxidation resistance of the substrate alloy.•The scale formed on Ti2AlC coating exhibits a four-layered microstructure in air.•No distinct oxide scale formed on the Ti2AlC coating in pure water vapor.The scale behavior of Ti2AlC coating at 750 °C in air and pure water vapor was investigated. A four-layered scale, a thick TiO2 and Al2O3 mix oxide outer layer, followed by a thin α-(Al, Cr)2O3 sublayer, a thick Fe2O3 and TiO2 mix oxide mid-layer and a thin Al2O3-rich oxide inner layer in sequence, developed on the Ti2AlC coatings in air. Whereas internal oxidation occurred, no distinct oxide scale formed on the Ti2AlC coating in the case of the oxidation in pure water vapor. The Ti2AlC coating improved the oxidation resistance of 316LSS in air, especially in wet air.

•MoS2-Ti composite coatings were deposited by a novel hybrid HIPIMS system.•Doping Ti enabled MoS2 coatings to grow into a dense amorphous structure.•Ti reacting with O to form titanium oxides inhibited the oxidation of MoS2.•Doped Ti improved the tribological behavior of pure MoS2 coating in ambient air.•The mechanism was discussed in terms of higher coating hardness and adhesion.The MoS2-Ti composite coatings were deposited by a hybrid high power impulse magnetron sputtering (HIPIMS) source of Ti combined with a direct current magnetron sputtering (DC-MS) source of MoS2. The composition, microstructure, mechanical and tribological behaviors of the MoS2-Ti composite coatings were investigated using the various analytical techniques (XPS, SEM, XRD, TEM, nano-indentation, scratch and ball-on-disk test). The results showed that doping Ti using HIPIMS technique enabled MoS2 coatings to grow in the form of a dense amorphous structure. The crystallization degree of the MoS2-Ti composite coatings decreased with the increase of doped titanium content. Ti reacting with O to form titanium oxides in the surface inhibited the oxidation of MoS2. The hardness and adhesion of the composite coatings reached its maximum within a certain range of Ti content. Doped Ti improved the tribological properties of pure MoS2 coatings in the atmospheric environment. The coefficient of friction (COF) decreased with the increase of Ti content. The lowest average COF at 0.04 and the wear rate at 10− 7 mm3 N− 1 m− 1 were achieved at the optimum of Ti content at 13.5 at.%. The improved tribological property was discussed in terms of the obtained higher hardness and better adhesion of the composite coatings combined with inhibition of MoS2 oxidation.