| The bit balling phenomenon of PDC bit during the exploitation of oil and gas resources is a common problem to be solved.Polytetrafluoroethylene(PTFE)has excellent self-lubricating properties,high temperature stability and chemical stability.It is commonly used in the preparation of hydrophobic coatings.It is suitable for surface modification of PDC bit,but a further improvement of hydrophobicity and wear resistance is needed.In this paper,three kinds of composite coatings of carbon fiber,graphene and polyphenylene sulfide modified polytetrafluoroethylene were prepared on a 35 CrMo steel substrate by one-step spraying method.The surface of the coatings and the wear tracks were observed by scanning electron microscopy and laser confocal microscopy.The two-dimensional morphology,three-dimensional morphology and the static contact angles of different composite coatings were measured,and the effects of filler type and proportion on the hydrophobicity and wear resistance of the modified PTFE composite coating were investigated.The main research results include:(1)Carbon fiber can effectively improve the tribological properties and hydrophobicity of the CF/PTFE composite coating.When the mass fraction of carbon fiber is 20%,the friction coefficient of CF/PTFE composite coating reaches the minimum value of 0.17±0.01,the wear rate also reaches the minimum value and the wear rate of pure PTFE coating is reduced by 29.7%.The main wear mechanism is adhesive wear and abrasive wear.At this time,the contact angle of the CF/PTFE composite coating was increased to 122.0 ° ± 2.0 °,showing excellent hydrophobicity.The transfer of fluorine from the inner layer of the coating to the outer layer in the CF/PTFE composite coating may be responsible for its excellent hydrophobicity.The carbon fiber inside the PTFE coating prevents large-area damage to the composite coating,and continuous and uniform transfer film on the counterpart may be an important cause of reduced wear.(2)Graphene modified PTFE composite coating has good tribological properties and hydrophobicity.When the graphene mass fraction is 3%,the friction coefficient of the composite coating is reduced to 0.11 ± 0.01 and is the lowest,and the wear rate is reduced by 63.8% compared with the pure PTFE coating.It has been found that a uniform and continuous transfer film adhered to the counterpart contributes to a reduction in wear rate and a better wear resistance of the GE/PTFE composite coating.The contact angle of the 3% GE/PTFE composite coating increased to 125.1 ° ± 1.8 °,showing good hydrophobicity.The analysis is considered to be because the graphene is uniformly dispersed in PTFE and forms a crosslinked structure,which increases the surface roughness of the composite coating,and the wear surface of the composite coating after the friction and wear test also exhibits good hydrophobicity,which proves that the composite coating The hydrophobicity of the layer has excellent maintenance,which is positive for the durability of the composite coating and its longevity.(3)The proper amount of polyphenylene sulfide can improve the tribological properties of the PPS/PTFE composite coating,but has little effect on the hydrophobicity.When the mass fraction of polyphenylene sulfide is 10%,the friction coefficient of the PPS/PTFE composite coating is reduced to 0.11 ± 0.01,and the wear rate is reduced by 75.6% compared to the wear rate of the pure PTFE coating.With the increase of the mass fraction of polyphenylene sulfide,the wear mechanism of PPS/PTFE composite coating is mainly due to the wear of abrasive grains and adhesive wear.Polyphenylene sulfide has little effect on the hydrophobic properties of PPS/PTFE composite coatings.The contact angles of polyphenylene sulfide modified polytetrafluoroethylene composite coatings with different mass fractions differ by about 3°,indicating PPS/PTFE composite coating.The hydrophobicity of the layer is more affected by the nature of the polytetrafluoroethylene itself. |
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