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Diamond-like carbon (DLC) coatings, as an excellent wear-resistant and low friction material, have been successfully applied as the surface protection and lubrication of various components. Recently, its application in the pipe fittings has gradually attracted the attention of the industry. In this paper, a plasma enhanced chemical vapor deposition (PECVD) technology was used to deposit a thick Si/Si-DLC/DLC multilayer composite coating inside a high aspect ratio pipe. The experimental results showed that the structures and properties of coatings strongly depended on deposition pressures. As the deposition pressure increased, the average thickness of the coating increased from 17 μm (50 mTorr) to 21.2 μm (110 mTorr) and its uniformity deviation continued to decreased until the pressure exceeded 100 mTorr, which reached the minimum value of 35.3%. When the deposition pressure rose, the coating hardness peaked at about 18.11 GPa (70 mTorr), and then it decreased to 14.86 GPa (110 mTorr). The friction coefficient and wear rate of the coating first decreased to 0.12 and 7.37 × 10−9 mm3/Nm (70 mTorr), respectively, and then slightly increased as the deposition pressure increased. In addition, the DLC coating we deposited also achieved a high adhesion strength of about 32 N (70 mTorr). In summary, the coating prepared at 70 mTorr had the best overall performance and was promised to be applied in pipeline protection industry. Unlabelled Image • Thick Si/Si-DLC/DLC multilayer coatings were deposited inside of long pipes by PECVD method. • The thickness and uniformity of the coating increase as the deposition pressure increases. • The coating prepared at 70 mTorr has the best tribological and mechanical performance • The main wear mechanism of thick DLC coatings is plowing and flaking. [ABSTRACT FROM AUTHOR]

Abstract Coating oxidation performance is a major concern in modern machining and other high temperature applications. This study presents TiAlCrN composite coatings with different Cr content prepared on a magnetron sputtering device. SEM, AFM and XRD were used to determine the structure of the coatings. It was found that the coatings show a solid solution of B1-NaCl face-centered cubic structure with [200] preferential orientation. As the Cr content increases, the particle size and roughness of the coating increase slightly, while the hardness of the coating decreases. Oxidation tests revealed that no significant oxidation occurs in all coatings below 800 °C. However, as the oxidation temperature increases to 1000 °C, the Ti 0.32 Al 0.38 Cr 0.30 N coating undergoes severe oxidation and the Ti 0.17 Al 0.19 Cr 0.64 N coating remains good. The oxide scale of the coatings after oxidation test is analysis by XPS depth profiling in details. XPS results revealed that the oxide scale of the Ti 0.32 Al 0.38 Cr 0.30 N coating changes from a dense Al rich oxide layer (800 °C) to a loose and discontinuous Ti Al rich oxide layer (1000 °C), which is the main reason for its poor oxidation resistance. However, the Ti 0.17 Al 0.19 Cr 0.64 N coating shows a top loose Ti Al rich oxide layer and a dense bottom Cr Al rich oxide layer. The presence of this dense and continuous Cr Al rich oxide layer can limit the rapid diffusion of Ti atoms to the surface while preventing the oxygen atoms from diffusing into the interior, which is the key to excellent oxidation resistance of the Ti 0.17 Al 0.19 Cr 0.64 N coatings. Highlights • The oxide scale of TiAlCrN coating was characterized by XPS depth profiling. • As the chromium content increases, the oxidation resistance of the TiAlCrN coating increases. • The excellent oxidation resistance strongly depended on the compact Cr Al rich oxide layer. • The presence of the Cr Al rich oxide layer can limit the rapid diffusion of Ti atoms to the surface. [ABSTRACT FROM AUTHOR]

High surface quality coatings play an important role in producing high precision coating tools for micromachining. This study focuses on the improvement of the coating surface quality by layered design method. The layered TiAlTaN/Ta coatings have been prepared by magnetron sputtering. SEM and AFM results revealed that the continuous growth of the columnar TiAlTaN crystals can be interrupted by layered design. The columnar crystal size of TiAlTaN coating decreased with the decreasing bilayer thickness. The coating surface roughness also gradually decreased from 36.6 ± 1.2 to 11.54 ± 0.6 to 8.9 ± 0.1 nm. Nanoidentation results showed an increasing coating hardness from 16 GPa to 20 GPa with decreasing bilayer thickness. Friction and wear test revealed that the coating friction coefficient increases from 0.70 to 0.93, then decreases to 0.62 with decreasing bilayer thickness. The layered method can improve mechanical and friction properties, meanwhile reducing surface roughness, which makes it a potentially promising method for fabricating high precision micromachining coating tools. [ABSTRACT FROM AUTHOR]

To improve the adaptability of GLC coatings in aqueous environment, a dense structure for GLC coatings was designed and constructed by nitrogen doping via PVD technique. The nitrogen content was tailored via tuning the nitrogen flow rate to optimize the tribological performances of the N-doped GLC coatings in water as well as to investigate the effects of different nitrogen contents. And the optimal nitrogen flow rate was 5 sccm. The results implied the nitrogen doping favored the increase of adhesion strength. The dense structure built by nitrogen doping entitled the N-GLC coatings to improved wear resistance in water and enhanced aqueous-adaptability, because the corrosion by water can be effectively inhibited compared with the column-structured nitrogen-free GLC coatings via PVD. [Display omitted] • The nitrogen modified GLC coatings with dense structure and better adhesion strength were constructed via PVD technique. • The nitrogen contents in the N-doped GLC coatings can be tailored by tuning the nitrogen flow rate in the PVD process. • The nitrogen-free GLC coating was failed in water environment, while the N-GLC coating with 5 sccm flow rate showed a lowest wear rate of 2.47 × 10-8 mm3/Nm. • The nitrogen doping contributed to the densification of the coatings and thus improved their aqueous-adaptability. [ABSTRACT FROM AUTHOR]