The Experts below are selected from a list of 135 Experts worldwide ranked by ideXlab platform
Liping Wang - One of the best experts on this subject based on the ideXlab platform.
-
Tailoring the mechanical and tribological properties of B4C/a-C Coatings by controlling the boron carbide content
Surface & Coatings Technology, 2017Co-Authors: Dongqing He, Lunlin Shang, Zhibin Lu, Guangan Zhang, Liping WangAbstract:Abstract Boron carbide doped DLC Coating can combine the property superiority of these two materials to create high-performance Carbon-Based Coating, while the final property of the composite Coating is strongly dependent on the proportion of Coating components. The aim of this study was to investigate the effect of boron carbide content on the mechanical and tribological properties of the magnetron sputtered B4C/a-C Coatings, as well as the relevant low friction mechanism. It was found that both the carbon matrix and introduced boron carbide were amorphous and the composite Coating exhibited typical columnar structure. Appropriate doping of boron carbide significantly enhanced Coating hardness, toughness as well as the adhesion strength and carrying ability, and all of them reached the optimal value when the B concentration was 2.92 at.%. It was also found that the B4C/a-C Coating with B 2.92 at.% exhibited the lowest steady friction coefficient about 0.05 and highest wear resistance at 20% RH. None of boric acid was formed on the sliding interface under the tested humidity range. Thus, the improved tribological properties were mainly attributed to the enhanced mechanical properties and friction-induced formation of an intact graphitized carbon transfer layer on the counterpart under specific humidity condition.
-
Preparation, Characterization, and Properties of Novel Carbon-Based nc-CrC/a-C(Al) Nanocomposite Coating
Tribology Transactions, 2014Co-Authors: Hao Chen, Shengguo Zhou, Liping WangAbstract:A novel Carbon-Based nc-CrC/a-C(Al) nanocomposite Coating was fabricated by combination of metallic Cr and Al doping via a multifunctional magnetron sputtering system. The composition and structure of the as-fabricated Coating were investigated by X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). This confirmed that the typical nanocrystallite/amorphous microstructure architecture can be achieved by codoping Cr and Al in the amorphous carbon matrix. A nano-indenter, interferometer, and ball-on-disc tribometer were used to test the hardness, internal stress, and tribological properties. The results show that the Carbon-Based nc-CrC/a-C(Al) nanocomposite Coating possesses superior mechanical properties with low internal stress and relatively high hardness as well as strong adhesion strength. Remarkably, the as-fabricated Carbon-Based Coating can achieve low friction and antiwear performance with a friction coefficient of 0.05 and w...
-
Testing Atmosphere Effect on Friction and Wear Behaviors of Duplex TiC/a-C(Al) Nanocomposite Carbon-Based Coating
Tribology Letters, 2012Co-Authors: Shengguo Zhou, Liping Wang, Qunji XueAbstract:Due to strongly tribological atmosphere sensitivity of Carbon-Based Coatings, it is of extreme significance to investigate their friction and wear behaviors in different atmospheres. In this letter, duplex nc-TiC/a-C(Al) nanocomposite Carbon-Based Coating coupled with high hardness, low internal stress and high adhesion strength was successfully fabricated using magnetron sputtering process. The friction and wear behaviors of as-fabricated Coating were evaluated in dry N2, humid N2, air, dry O2, and humid O2 atmospheres, respectively. Results show that the as-fabricated Coating possesses very high friction and wear due to the strong covalent bond interactions at the sliding interface caused by the free σ-bonds on the Coating surface in dry N2 atmosphere. Whereas the free σ-bonds can be efficiently terminated and passivated by water and/or oxygen molecules to weaken the strong covalent bond interactions to result in low friction and wear of Coating in humid N2, air, dry O2, and humid O2 atmospheres. The compact and homogeneous carbonaceous tribo-layer on the counterpart is mainly responsible for the lowest friction and wear of Coating in humid N2 atmosphere. Whereas the tribo-layer can be restrained to a certain extent by the tribo-chemical reaction, especially it results in a nearly negligible carbonaceous tribo-layer on the counterpart in dry O2 atmosphere, which is mainly responsible for largely increased friction and wear of Coating.
-
Tribo-pair dependence of friction and wear moisture sensitivity for a-C:Si:Al Carbon-Based Coating
Journal of Non-Crystalline Solids, 2012Co-Authors: Shengguo Zhou, Liping Wang, Qunji XueAbstract:Abstract Providing a low, predictable and stable friction as well as low wear for mechanical components across a wide range from dry to wet atmosphere is of great importance in many engineering applications, the urgent challenge is to control tribological moisture sensitivity of their protective Coatings. In this paper, the a-C:Si:Al Carbon-Based Coating was fabricated successfully using multifunctional magnetron sputtering system. The microstructure and mechanical properties of as-fabricated Coating were investigated; especially the friction and wear of Coating sliding against Si 3 N 4 , SiO 2 , GCr15, brass and aluminum counterparts were evaluated under different relative humidity atmospheres. Results showed that the as-fabricated a-C:Si:Al Carbon-Based Coating presented typical amorphous microstructure and good combined mechanical properties. Under low relative humidity conditions, the graphitized carbon tribo-layers on the contact surfaces were responsible for low friction; under high relative humidity conditions, the low shear strength colloidal silica on the contact surfaces induced by tribo-chemical reaction were mainly responsible for low friction. In particular, the lowest tribological moisture sensitivity can be achieved by the a-C:Si:Al/SiO 2 pair, which was mainly attributed to the formation of tribo-layers on the contact surfaces induced by the graphitization and tribo-chemical reaction under different relative humidity conditions. These indicate that the a-C:Si:Al Carbon-Based Coating might be a good candidate as low tribological moisture sensitivity material in engineering applications.
-
duplex doped nanocomposite carbon based Coating with self lubricating performance
Diamond and Related Materials, 2012Co-Authors: Shengguo Zhou, Liping WangAbstract:Abstract Nanocomposite TiC/a-C and TiC/a-C:Al Carbon-Based Coatings were fabricated on stainless steel and silicon wafer substrates. X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used to investigate the composition and structure of as-fabricated Coatings. Nanoindenter, interferometer, scratch tester and ball-on-disc tribometer were used to evaluate the mechanical and tribological properties. Results showed that the TiC nanocrystallites were formed and uniformly dispersed in the amorphous carbon matrix by incorporating strong-carbide-forming Ti metal while the size of TiC grain and surface roughness were decreased by co-incorporating weak-carbide-forming Al metal. Particularly, the co-incorporation of Al could drastically diminish the magnitude of internal stress, improve adhesion strength and maintain relatively high hardness for as-fabricated Coating. As a result, the duplex doped nc-TiC/a-C:Al Coating achieved lower friction coefficient and specific wear rate compared to simplex Ti-doped nc-TiC/a-C Coating. Mechanism analysis revealed that the improved self-lubricating and anti-wear performances of this nc-TiC/a-C:Al Coating were mainly attributed to the good combining mechanical properties and easily formed continuous and compacted graphitized interlayer on the contact area.
Shengguo Zhou - One of the best experts on this subject based on the ideXlab platform.
-
Preparation, Characterization, and Properties of Novel Carbon-Based nc-CrC/a-C(Al) Nanocomposite Coating
Tribology Transactions, 2014Co-Authors: Hao Chen, Shengguo Zhou, Liping WangAbstract:A novel Carbon-Based nc-CrC/a-C(Al) nanocomposite Coating was fabricated by combination of metallic Cr and Al doping via a multifunctional magnetron sputtering system. The composition and structure of the as-fabricated Coating were investigated by X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). This confirmed that the typical nanocrystallite/amorphous microstructure architecture can be achieved by codoping Cr and Al in the amorphous carbon matrix. A nano-indenter, interferometer, and ball-on-disc tribometer were used to test the hardness, internal stress, and tribological properties. The results show that the Carbon-Based nc-CrC/a-C(Al) nanocomposite Coating possesses superior mechanical properties with low internal stress and relatively high hardness as well as strong adhesion strength. Remarkably, the as-fabricated Carbon-Based Coating can achieve low friction and antiwear performance with a friction coefficient of 0.05 and w...
-
Testing Atmosphere Effect on Friction and Wear Behaviors of Duplex TiC/a-C(Al) Nanocomposite Carbon-Based Coating
Tribology Letters, 2012Co-Authors: Shengguo Zhou, Liping Wang, Qunji XueAbstract:Due to strongly tribological atmosphere sensitivity of Carbon-Based Coatings, it is of extreme significance to investigate their friction and wear behaviors in different atmospheres. In this letter, duplex nc-TiC/a-C(Al) nanocomposite Carbon-Based Coating coupled with high hardness, low internal stress and high adhesion strength was successfully fabricated using magnetron sputtering process. The friction and wear behaviors of as-fabricated Coating were evaluated in dry N2, humid N2, air, dry O2, and humid O2 atmospheres, respectively. Results show that the as-fabricated Coating possesses very high friction and wear due to the strong covalent bond interactions at the sliding interface caused by the free σ-bonds on the Coating surface in dry N2 atmosphere. Whereas the free σ-bonds can be efficiently terminated and passivated by water and/or oxygen molecules to weaken the strong covalent bond interactions to result in low friction and wear of Coating in humid N2, air, dry O2, and humid O2 atmospheres. The compact and homogeneous carbonaceous tribo-layer on the counterpart is mainly responsible for the lowest friction and wear of Coating in humid N2 atmosphere. Whereas the tribo-layer can be restrained to a certain extent by the tribo-chemical reaction, especially it results in a nearly negligible carbonaceous tribo-layer on the counterpart in dry O2 atmosphere, which is mainly responsible for largely increased friction and wear of Coating.
-
Tribo-pair dependence of friction and wear moisture sensitivity for a-C:Si:Al Carbon-Based Coating
Journal of Non-Crystalline Solids, 2012Co-Authors: Shengguo Zhou, Liping Wang, Qunji XueAbstract:Abstract Providing a low, predictable and stable friction as well as low wear for mechanical components across a wide range from dry to wet atmosphere is of great importance in many engineering applications, the urgent challenge is to control tribological moisture sensitivity of their protective Coatings. In this paper, the a-C:Si:Al Carbon-Based Coating was fabricated successfully using multifunctional magnetron sputtering system. The microstructure and mechanical properties of as-fabricated Coating were investigated; especially the friction and wear of Coating sliding against Si 3 N 4 , SiO 2 , GCr15, brass and aluminum counterparts were evaluated under different relative humidity atmospheres. Results showed that the as-fabricated a-C:Si:Al Carbon-Based Coating presented typical amorphous microstructure and good combined mechanical properties. Under low relative humidity conditions, the graphitized carbon tribo-layers on the contact surfaces were responsible for low friction; under high relative humidity conditions, the low shear strength colloidal silica on the contact surfaces induced by tribo-chemical reaction were mainly responsible for low friction. In particular, the lowest tribological moisture sensitivity can be achieved by the a-C:Si:Al/SiO 2 pair, which was mainly attributed to the formation of tribo-layers on the contact surfaces induced by the graphitization and tribo-chemical reaction under different relative humidity conditions. These indicate that the a-C:Si:Al Carbon-Based Coating might be a good candidate as low tribological moisture sensitivity material in engineering applications.
-
duplex doped nanocomposite carbon based Coating with self lubricating performance
Diamond and Related Materials, 2012Co-Authors: Shengguo Zhou, Liping WangAbstract:Abstract Nanocomposite TiC/a-C and TiC/a-C:Al Carbon-Based Coatings were fabricated on stainless steel and silicon wafer substrates. X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used to investigate the composition and structure of as-fabricated Coatings. Nanoindenter, interferometer, scratch tester and ball-on-disc tribometer were used to evaluate the mechanical and tribological properties. Results showed that the TiC nanocrystallites were formed and uniformly dispersed in the amorphous carbon matrix by incorporating strong-carbide-forming Ti metal while the size of TiC grain and surface roughness were decreased by co-incorporating weak-carbide-forming Al metal. Particularly, the co-incorporation of Al could drastically diminish the magnitude of internal stress, improve adhesion strength and maintain relatively high hardness for as-fabricated Coating. As a result, the duplex doped nc-TiC/a-C:Al Coating achieved lower friction coefficient and specific wear rate compared to simplex Ti-doped nc-TiC/a-C Coating. Mechanism analysis revealed that the improved self-lubricating and anti-wear performances of this nc-TiC/a-C:Al Coating were mainly attributed to the good combining mechanical properties and easily formed continuous and compacted graphitized interlayer on the contact area.
-
Achieving Low Tribological Moisture Sensitivity by a-C:Si:Al Carbon-Based Coating
Tribology Letters, 2011Co-Authors: Shengguo Zhou, Liping Wang, Qunji XueAbstract:Owing to the requirements of the stable operation for mechanical components, the urgent challenges are to control tribological moisture sensitivity of protective Coatings. In this letter, a-C:Si and a-C:Si:Al Carbon-Based Coatings were successfully fabricated via magnetron sputtering Si, Al, and C. The microstructure, mechanical properties, and tribological moisture sensitivity of as-fabricated Carbon-Based Coatings were comparatively investigated. Results showed that the as-fabricated a-C:Si and a-C:Si:Al Coatings were dominated by typical amorphous structure. The co-introduction of Al could effectively relax internal stress and improve adhesive strength as well as maintain the moderately high hardness for the as-fabricated Coating. The striking improvement in tribological moisture sensitivity of a-C:Si:Al Carbon-Based Coating was mainly attributed to the superior mechanical properties and the formation of continuously compacted graphitized tribofilm under low relative humidity condition as well as low shear strength colloidal silica tribofilm under high relative humidity condition. The good balance between the hardness and toughness, low internal stress, and superior low tribological moisture sensitivity of a-C:Si:Al Coating make it a good candidate for solid lubricating Coating in engineering applications.
Papken Eh. Hovsepian - One of the best experts on this subject based on the ideXlab platform.
-
Friction and wear behaviour of Mo–W doped Carbon-Based Coating during boundary lubricated sliding
Applied Surface Science, 2016Co-Authors: Papken Eh. Hovsepian, Paranjayee Mandal, Arutiun P. Ehiasarian, György Sáfrán, Roel Tietema, Dave DoerwaldAbstract:Abstract A molybdenum and tungsten doped Carbon-Based Coating (Mo–W–C) was developed in order to provide low friction in boundary lubricated sliding condition at ambient and at high temperature. The Mo–W–C Coating showed the lowest friction coefficient among a number of commercially available state-of-the-art DLC Coatings at ambient temperature. At elevated temperature (200 °C), Mo–W–C Coating showed a significant reduction in friction coefficient with sliding distance in contrast to DLC Coatings. Raman spectroscopy revealed the importance of combined Mo and W doping for achieving low friction at both ambient and high temperature. The significant decrease in friction and wear rate was attributed to the presence of graphitic carbon debris (from Coating) and ‘in situ’ formed metal sulphides (WS2 and MoS2, where metals were supplied from Coating and sulphur from engine oil) in the transfer layer.
-
Wear mechanism of Mo-W doped Carbon-Based Coating during boundary lubricated sliding
2015Co-Authors: Paranjayee Mandal, Arutiun P. Ehiasarian, Papken Eh. HovsepianAbstract:The high temperature tribological applications of state-of-the-art diamond-like-carbon (DLC) Coatings in automotive industry are often compromised due to their poor adhesion strength and low thermal stability. A molybdenum and tungsten doped Carbon-Based Coating (Mo−W−C) is developed in order to overcome these limitations and to enhance tribological performance during boundary lubricated sliding at ambient and elevated temperature. The Coating was deposited utilising HIPIMS technology. Mo−W−C Coating showed lowest mean friction coefficient (µ=0.033) compared to a number of commercially available state-of-the-art DLC Coatings when pin-on-disc experiments were carried out at ambient temperature. Similarly at 200°C, a significant reduction in friction coefficient was observed for Mo−W−C Coating with increase in sliding distance unlike DLC Coating. Raman spectroscopy revealed importance of combined Mo and W doping and tribochemically reactive wear mechanism of Mo−W−C Coating during sliding. The significant decrease in friction and wear rate was attributed to the presence of graphitic carbon particles (from Coating) and 'in-situ' formed metal sulphides (WS2 and MoS2, where metals from Coating and sulphur from oil) in transfer layer.
-
Tribological behaviour of Mo − W doped Carbon-Based Coating at ambient condition
Tribology International, 2015Co-Authors: Paranjayee Mandal, Arutiun P. Ehiasarian, Papken Eh. HovsepianAbstract:Poor adhesion strength and low thermal stability often restrict the tribological applications of the state-of-the-art diamond-like-carbon Coatings in automotive industry. A novel Carbon-Based Coating doped with molybdenum and tungsten (Mo–W–C) is deposited using the advantages of HIPIMS to overcome these limitations and to provide enhanced tribological performance. Low friction (µ=0.335 against steel counterpart) and high wear resistance (Kc=3.87×10−16 m3 N−1 m−1) are observed after 7.5 km sliding distance and the Coating remains intact within the wear track after sliding. It is concluded that the tribological performance of Mo–W–C Coating at ambient condition excels due to its dense microstructure, interfacial adhesion strength and in-situ formation of solid lubricants such as graphitic carbon particles, MoO3 and Magneli phase oxides of molybdenum and tungsten in the transfer layer during sliding.
-
Isothermal and dynamic oxidation behaviour of Mo–W doped Carbon-Based Coating
Applied Surface Science, 2015Co-Authors: Paranjayee Mandal, Arutiun P. Ehiasarian, Papken Eh. HovsepianAbstract:Abstract The oxidation behaviour of Mo–W doped Carbon-Based Coating (Mo–W–C) is investigated in elevated temperature (400–1000 °C). Strong metallurgical bond between Mo–W–C Coating and substrate prevents any sort of delamination during heat-treatment. Isothermal oxidation tests show initial growth of metal oxides at 500 °C, however graphitic nature of the as-deposited Coating is preserved. The oxidation progresses with further rise in temperature and the substrate is eventually exposed at 700 °C. The performance of Mo–W–C Coating is compared with a state-of-the-art DLC(Cr/Cr–WC/W:C–H/a:C–H) Coating, which shows preliminary oxidation at 400 °C and local delamination of the Coating at 500 °C leading to substrate exposure. The graphitisation starts at 400 °C and the diamond-like structure is completely converted into the graphite-like structure at 500 °C. Dynamic oxidation behaviour of both the Coatings is investigated using Thermo-gravimetric analysis carried out with a slow heating rate of 1 °C/min from ambient temperature to 1000 °C. Mo–W–C Coating resists oxidation up to ∼800 °C whereas delamination of DLC(Cr/Cr–WC/W:C–H/a:C–H) Coating is observed beyond ∼380 °C. In summary, Mo–W–C Coating provides improved oxidation resistance at elevated temperature compared to DLC(Cr/Cr–WC/W:C–H/a:C–H) Coating.
Paranjayee Mandal - One of the best experts on this subject based on the ideXlab platform.
-
Friction and wear behaviour of Mo–W doped Carbon-Based Coating during boundary lubricated sliding
Applied Surface Science, 2016Co-Authors: Papken Eh. Hovsepian, Paranjayee Mandal, Arutiun P. Ehiasarian, György Sáfrán, Roel Tietema, Dave DoerwaldAbstract:Abstract A molybdenum and tungsten doped Carbon-Based Coating (Mo–W–C) was developed in order to provide low friction in boundary lubricated sliding condition at ambient and at high temperature. The Mo–W–C Coating showed the lowest friction coefficient among a number of commercially available state-of-the-art DLC Coatings at ambient temperature. At elevated temperature (200 °C), Mo–W–C Coating showed a significant reduction in friction coefficient with sliding distance in contrast to DLC Coatings. Raman spectroscopy revealed the importance of combined Mo and W doping for achieving low friction at both ambient and high temperature. The significant decrease in friction and wear rate was attributed to the presence of graphitic carbon debris (from Coating) and ‘in situ’ formed metal sulphides (WS2 and MoS2, where metals were supplied from Coating and sulphur from engine oil) in the transfer layer.
-
Wear mechanism of Mo-W doped Carbon-Based Coating during boundary lubricated sliding
2015Co-Authors: Paranjayee Mandal, Arutiun P. Ehiasarian, Papken Eh. HovsepianAbstract:The high temperature tribological applications of state-of-the-art diamond-like-carbon (DLC) Coatings in automotive industry are often compromised due to their poor adhesion strength and low thermal stability. A molybdenum and tungsten doped Carbon-Based Coating (Mo−W−C) is developed in order to overcome these limitations and to enhance tribological performance during boundary lubricated sliding at ambient and elevated temperature. The Coating was deposited utilising HIPIMS technology. Mo−W−C Coating showed lowest mean friction coefficient (µ=0.033) compared to a number of commercially available state-of-the-art DLC Coatings when pin-on-disc experiments were carried out at ambient temperature. Similarly at 200°C, a significant reduction in friction coefficient was observed for Mo−W−C Coating with increase in sliding distance unlike DLC Coating. Raman spectroscopy revealed importance of combined Mo and W doping and tribochemically reactive wear mechanism of Mo−W−C Coating during sliding. The significant decrease in friction and wear rate was attributed to the presence of graphitic carbon particles (from Coating) and 'in-situ' formed metal sulphides (WS2 and MoS2, where metals from Coating and sulphur from oil) in transfer layer.
-
Tribological behaviour of Mo − W doped Carbon-Based Coating at ambient condition
Tribology International, 2015Co-Authors: Paranjayee Mandal, Arutiun P. Ehiasarian, Papken Eh. HovsepianAbstract:Poor adhesion strength and low thermal stability often restrict the tribological applications of the state-of-the-art diamond-like-carbon Coatings in automotive industry. A novel Carbon-Based Coating doped with molybdenum and tungsten (Mo–W–C) is deposited using the advantages of HIPIMS to overcome these limitations and to provide enhanced tribological performance. Low friction (µ=0.335 against steel counterpart) and high wear resistance (Kc=3.87×10−16 m3 N−1 m−1) are observed after 7.5 km sliding distance and the Coating remains intact within the wear track after sliding. It is concluded that the tribological performance of Mo–W–C Coating at ambient condition excels due to its dense microstructure, interfacial adhesion strength and in-situ formation of solid lubricants such as graphitic carbon particles, MoO3 and Magneli phase oxides of molybdenum and tungsten in the transfer layer during sliding.
-
Isothermal and dynamic oxidation behaviour of Mo–W doped Carbon-Based Coating
Applied Surface Science, 2015Co-Authors: Paranjayee Mandal, Arutiun P. Ehiasarian, Papken Eh. HovsepianAbstract:Abstract The oxidation behaviour of Mo–W doped Carbon-Based Coating (Mo–W–C) is investigated in elevated temperature (400–1000 °C). Strong metallurgical bond between Mo–W–C Coating and substrate prevents any sort of delamination during heat-treatment. Isothermal oxidation tests show initial growth of metal oxides at 500 °C, however graphitic nature of the as-deposited Coating is preserved. The oxidation progresses with further rise in temperature and the substrate is eventually exposed at 700 °C. The performance of Mo–W–C Coating is compared with a state-of-the-art DLC(Cr/Cr–WC/W:C–H/a:C–H) Coating, which shows preliminary oxidation at 400 °C and local delamination of the Coating at 500 °C leading to substrate exposure. The graphitisation starts at 400 °C and the diamond-like structure is completely converted into the graphite-like structure at 500 °C. Dynamic oxidation behaviour of both the Coatings is investigated using Thermo-gravimetric analysis carried out with a slow heating rate of 1 °C/min from ambient temperature to 1000 °C. Mo–W–C Coating resists oxidation up to ∼800 °C whereas delamination of DLC(Cr/Cr–WC/W:C–H/a:C–H) Coating is observed beyond ∼380 °C. In summary, Mo–W–C Coating provides improved oxidation resistance at elevated temperature compared to DLC(Cr/Cr–WC/W:C–H/a:C–H) Coating.
-
Tribological study of novel metal-doped Carbon-Based Coatings with enhanced thermal stability.
2015Co-Authors: Paranjayee MandalAbstract:Low friction and high temperature wear resistant PVD Coatings are in high demand for use on engine components, which operate in extreme environment. Diamond-like-carbon (DLC) Coatings are extensively used for this purpose due to their excellent tribological properties. However, DLC degrades at high temperature and pressure conditions leading to significant increase in friction and wear rate even in the presence of lubricant. To withstand high working temperature and simultaneously maintain improved tribological properties in lubricated condition at ambient and at high temperature, both the transitional metals Mo and W are simultaneously introduced in a Carbon-Based Coating (Mo-W-C) for the first time utilising the benefits of smart material combination and High Power Impulse Magnetron Sputtering (HIPIMS).This research includes development of Mo-W-C Coating and investigation of thermal stability and tribological properties at ambient and high temperatures. The as-deposited Mo-W-C Coating contains nanocrystalline almost X-ray amorphous structure and show dense microstructure, good adhesion with substrate (Lc -80 N) and high hardness (-17 GPa). During boundary lubricated sliding (commercially available engine oil without friction modifier used as lubricant) at ambient temperature, Mo-W-C Coating outperforms commercially available state-of-the-art DLC Coatings by providing significantly low friction (u- 0.03 - 0.05) and excellent wear resistance (no measurable wear). When lubricated sliding tests are carried out at 200°C, Mo-W-C Coating provides low friction similar to ambient temperature, whereas degradation of DLC Coating properties fails to maintain low friction coefficient.A range of surface analyses techniques reveal "in-situ" formation of solid lubricants (WS2 and M0S2) at the tribo-contacts due to tribochemically reactive wear mechanism at ambient and high temperature. Mo-W-C Coating reacts with EP additives present in the engine oil during sliding to form WS2 and M0S2. This mechanism is believed to be the key-factor for low friction properties of Mo-W-C Coating and presence of graphitic carbon particles further benefits the friction behaviour. It is observed that low friction is achieved mostly due to formation of WS2 at ambient temperature, whereas formation of both WS2 and M0S2 significantly decreases the friction of Mo-W-C Coating at high temperature. This further indicates importance of combined Mo and W doping over single-metal doping into Carbon-Based Coatings.Isothermal oxidation tests indicate that Mo-W-C Coating preserves it's as-deposited graphitic nature up to 500°C, whereas local delamination of DLC Coating leads to substrate exposure and loss of its diamond-like structure at the same temperature. Further, thermo-gravimetric tests confirm excellent thermal stability of Mo-W-C Coating compared to DLC. Mo-W-C Coating resists oxidation up to ~800°C and no Coating delamination is observed due to retained Coating integrity and its strong adhesion with substrate. On the other hand, state-of-the-art DLC Coating starts to delaminate beyond ~380°C.The test results confirm that Mo-W-C Coating sustains high working temperature and simultaneously maintains improved tribological properties during boundary lubricated condition at ambient and high temperature. Thus Mo-W-C Coating is a suitable candidate for low friction and high temperature wear resistant applications compared to commercially available state-of-the-art DLC Coatings.
Qunji Xue - One of the best experts on this subject based on the ideXlab platform.
-
Testing Atmosphere Effect on Friction and Wear Behaviors of Duplex TiC/a-C(Al) Nanocomposite Carbon-Based Coating
Tribology Letters, 2012Co-Authors: Shengguo Zhou, Liping Wang, Qunji XueAbstract:Due to strongly tribological atmosphere sensitivity of Carbon-Based Coatings, it is of extreme significance to investigate their friction and wear behaviors in different atmospheres. In this letter, duplex nc-TiC/a-C(Al) nanocomposite Carbon-Based Coating coupled with high hardness, low internal stress and high adhesion strength was successfully fabricated using magnetron sputtering process. The friction and wear behaviors of as-fabricated Coating were evaluated in dry N2, humid N2, air, dry O2, and humid O2 atmospheres, respectively. Results show that the as-fabricated Coating possesses very high friction and wear due to the strong covalent bond interactions at the sliding interface caused by the free σ-bonds on the Coating surface in dry N2 atmosphere. Whereas the free σ-bonds can be efficiently terminated and passivated by water and/or oxygen molecules to weaken the strong covalent bond interactions to result in low friction and wear of Coating in humid N2, air, dry O2, and humid O2 atmospheres. The compact and homogeneous carbonaceous tribo-layer on the counterpart is mainly responsible for the lowest friction and wear of Coating in humid N2 atmosphere. Whereas the tribo-layer can be restrained to a certain extent by the tribo-chemical reaction, especially it results in a nearly negligible carbonaceous tribo-layer on the counterpart in dry O2 atmosphere, which is mainly responsible for largely increased friction and wear of Coating.
-
Tribo-pair dependence of friction and wear moisture sensitivity for a-C:Si:Al Carbon-Based Coating
Journal of Non-Crystalline Solids, 2012Co-Authors: Shengguo Zhou, Liping Wang, Qunji XueAbstract:Abstract Providing a low, predictable and stable friction as well as low wear for mechanical components across a wide range from dry to wet atmosphere is of great importance in many engineering applications, the urgent challenge is to control tribological moisture sensitivity of their protective Coatings. In this paper, the a-C:Si:Al Carbon-Based Coating was fabricated successfully using multifunctional magnetron sputtering system. The microstructure and mechanical properties of as-fabricated Coating were investigated; especially the friction and wear of Coating sliding against Si 3 N 4 , SiO 2 , GCr15, brass and aluminum counterparts were evaluated under different relative humidity atmospheres. Results showed that the as-fabricated a-C:Si:Al Carbon-Based Coating presented typical amorphous microstructure and good combined mechanical properties. Under low relative humidity conditions, the graphitized carbon tribo-layers on the contact surfaces were responsible for low friction; under high relative humidity conditions, the low shear strength colloidal silica on the contact surfaces induced by tribo-chemical reaction were mainly responsible for low friction. In particular, the lowest tribological moisture sensitivity can be achieved by the a-C:Si:Al/SiO 2 pair, which was mainly attributed to the formation of tribo-layers on the contact surfaces induced by the graphitization and tribo-chemical reaction under different relative humidity conditions. These indicate that the a-C:Si:Al Carbon-Based Coating might be a good candidate as low tribological moisture sensitivity material in engineering applications.
-
Achieving Low Tribological Moisture Sensitivity by a-C:Si:Al Carbon-Based Coating
Tribology Letters, 2011Co-Authors: Shengguo Zhou, Liping Wang, Qunji XueAbstract:Owing to the requirements of the stable operation for mechanical components, the urgent challenges are to control tribological moisture sensitivity of protective Coatings. In this letter, a-C:Si and a-C:Si:Al Carbon-Based Coatings were successfully fabricated via magnetron sputtering Si, Al, and C. The microstructure, mechanical properties, and tribological moisture sensitivity of as-fabricated Carbon-Based Coatings were comparatively investigated. Results showed that the as-fabricated a-C:Si and a-C:Si:Al Coatings were dominated by typical amorphous structure. The co-introduction of Al could effectively relax internal stress and improve adhesive strength as well as maintain the moderately high hardness for the as-fabricated Coating. The striking improvement in tribological moisture sensitivity of a-C:Si:Al Carbon-Based Coating was mainly attributed to the superior mechanical properties and the formation of continuously compacted graphitized tribofilm under low relative humidity condition as well as low shear strength colloidal silica tribofilm under high relative humidity condition. The good balance between the hardness and toughness, low internal stress, and superior low tribological moisture sensitivity of a-C:Si:Al Coating make it a good candidate for solid lubricating Coating in engineering applications.