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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]

Adhesive wear is one of the major reasons for short tool life during machining titanium alloys. This study presents a new kind of low adhesive wear TaO functional coating prepared by magnetron sputtering. The composite coating is composed by two layers of a solid solution TiAlTaN in bottom and a TaO (Ta 2 O 5 or TaO x ) on top. Tool life of the TiAlTaN/TaO coatings is increased more than triple the TiAlTaN single coating by titanium cutting experiments. Cutting performance of commercial TiAlN-based coated tool is increased 267% after coating the TaO on the surface. Friction and wear between the coatings and Ti6Al4V counterpart have been conducted. The results show that both the friction coefficient of the coatings (from 1.05 to 0.82) and surface roughness (from 12.2 ± 0.6 to 7.1 ± 0.1 nm) are decreased by increasing TaO thickness from 0 to 150 nm. The adhesive bonds between coating and titanium also reduce with increasing the TaO thickness. This leads to the significantly reduction of the adhesion at the cutting tool tip after coated the TaO coating. This is because that the titanium is not easy to bind with the TaO coating by the calculated positive interaction energy between the Ta 2 O 5 surface and pure Ti. [ABSTRACT FROM AUTHOR]

Research on the relationship of microstructure and properties of coated tools such as TiAlN and TiAlSiN plays a key role in obtaining the needed cutting performance in titanium machining. In this study, three kinds of coatings of TiAlN, TiAlSiN monolayer and TiAlN/TiAlSiN composite multilayer have been fabricated by magnetron sputtering method. It is found that the coating structure changes from columnar growth to nanocrystal growth by doping Si element. The TiAlN/TiAlSiN coating is composed by a coarse columnar TiAlN bottom layer and a fine nanocrystalline TiAlSiN top layer. Premature spalling problem (Lc2) is improved by forming the TiAlN/TiAlSiN multilayer structure. Titanium cutting experiment shows that the major wear mechanism of these coated tools is adhesive wear and chipping. The TiAlSiN coated tool has the longest cutting distance at various cutting speeds in these three kinds of coatings. This is because less built-up edge and chipping are generated at the cutting edge due to the dense nanocrystal structure, high hardness and good oxidation resistance of TiAlSiN coating. Therefore, the TiAlSiN coating with dense structure, high hardness and good oxidation resistance is recommended to use in high speed turning titanium. [ABSTRACT FROM AUTHOR]

Rotational speed has an important influence on the performance of coating materials. The a-C:Ta composite coatings were prepared by controlling the substrate rotational speed during deposition process using PVD technique. The results showed that the coating transformed from dense structure to columnar structure. Due to the changes of deposition time and the vapor incident angle of the sputtering ions, the sp2 hybrid structure increased and the C–Ta bonds contents decreased as a function of the rotational speed, which led to the improvement of adhesion force. The average friction coefficient of the composite coatings did not fluctuate significantly for the amorphous carbon matrix and the transfer films formed during friction, while the wear rates were gradually increased. The sample at 0.5 rpm possessed the lowest wear rate, which was mainly associated with the cooperative behavior of the dense structure and the formation of TaC nanoclusters in the composite coating. [ABSTRACT FROM AUTHOR]

The high-throughput preparation of MoS 2 -(Cr, Nb, Ti, Al, V) composite coatings was achieved by multi-targets co-sputtering method. Based on the obtained friction coefficient of 236 samples as the criterion, four samples with the largest difference in friction coefficient were screened out for further detailed investigations. The results demonstrated that high metal doping amount can dense the coating and reduce the particle size. As the doping content increased, the coating transformed from nanocrystalline to amorphous structure. Consequently, MoS 2 -(Cr, Nb, Ti, Al, V) composite coatings with high doping levels presented higher hardness and better atmospheric tribological properties. Moreover, the Cr and Al dopants can better inhibit the oxidation of MoS 2 than Nb, Ti and V dopants owing to the denser oxide films. • More than two hundreds of doped MoS 2 coatings are prepared by high throughput preparation. • The coatings with high doping contents own higher hardness and better tribological properties. • As the doping content increases, the coating transform from nanocrystalline to amorphous structure. • The Cr and Al dopants can better inhibit the oxidation of MoS 2 than Nb, Ti and V dopants. • The P8 sample owns a friction coefficient of about 0.03 and wear rate of 3.16 × 10−7 mm3/(N.•m). [ABSTRACT FROM AUTHOR]