Synthesis and friction behavior of chemically vapor deposited composite coatings containing discrete TiN and MoS₂ phases

Composite coatings containing discrete crystalline phases of TiN and MoS₂ were deposited on Si, graphite, and Ti-6Al-4V alloy substrates by simultaneous chemical vapor deposition. MoF₆ and H₂S were utilized as the precursors for MoS₂ formation, while Ti((CH₃)₂N)₄ and NH₃ were used for TiN deposition. The composition and microstructure of the coatings were investigated by X-ray diffraction, Auger electron spectroscopy, and transmission electron microscopy. The molar ratios of TiN and MoS₂ in the composite microstructure could be controlled by adjusting the MoF₆ concentration in the reagent mixture. Encouraging friction and wear characteristics against silicon nitride were obtained for a composite coating which was rich in MoS₂ at the coating surface, with TiN as the major phase near the substrate interface. Friction coefficients at room temperature in air were typically in the range of 0.07 to 0.3. The friction coefficients remained comparable at 573 K, but increased to 0.7 to 1.0 at 673 K. A friction coefficient value of ∼0.3 was, however, obtained from a composite coating tested at 973 K.