Friction behavior of TiN–MoS2/PTFE composite coatings in dry sliding against SiC

To improve the dry friction behavior of traditional hard coatings, MoS₂/PTFE lubricating coatings were prepared on the PVD TiN-coated cemented carbide using spray method. The influences of MoS₂/PTFE lubricating coatings on the primary characteristics of TiN coatings were investigated. Reciprocating sliding tests were carried out with the TiN–MoS₂/PTFE coated specimen (T-M-P) under dry sliding conditions, and the tribological behaviors were compared to those of the TiN-coated one (T-N). The test results indicated that the adhesion force of coatings with substrate for T-M-P specimen increased, the surface micro-hardness, roughness and friction coefficient significantly decreased. Meanwhile, the surface adhesions and abrasion grooves of T-M-P specimen were reduced, and the main wear forms of T-M-P were abrasion wear and coating delamination. The MoS₂/PTFE lubricating coatings can be considered effective to improve the friction properties of traditional hard coatings.     

Friction behavior of PTFE-coated Si3N4/TiC ceramics fabricated by spray technique under dry friction

PTFE coatings were deposited on the Si₃N₄/TiC ceramic substrate by using spray technology. The surface and cross-section micrographs, adhesive force of coatings with substrate, surface roughness and micro-hardness of the coated ceramics were examined. The friction and wear behaviors of ceramic samples with and without coatings were investigated through carrying out dry sliding friction tests against WC/Co ball. The test results indicated that the coated ceramics exhibited rougher surface and lower micro-hardness, and the PTFE coatings can significantly reduce the surface friction and adhesive wear of ceramics. The friction performance of PTFE-coated sample was affected by applied load due to the lower surface hardness and shear strength of coatings, and the main wear failure mechanisms were abrasion wear, coating delamination and flaking. It can be considered that deposition of PTFE coatings is a promising approach to improve the friction and wear behavior of ceramic substrate.     

Effect of specimen orientation and heat treatment on electroless Ni-PTFE-MoS<Subscript>2</Subscript> composite coatings

In this study, the effects of simultaneous co-deposition of polytetrafluoroethylene (PTFE) and MoS₂ particles on tribological properties of electroless nickel (EN) coating were studied. The influences of specimen orientation and heat treatment on EN-PTFE-MoS₂ composite coatings were also investigated. Scanning electron microscopy was used to study the morphology of coatings and the distributions of the lubricant particles in the deposits. Chemical analyses of coatings were done by electron dispersive spectrometry. The phases of the coatings were identified by X-ray diffraction utilizing CuKα radiation. Wear and friction properties of the coatings were also determined by pin-on-disk wear tester. The wear investigations showed that the EN-PTFE-MoS₂ composite coating performs better than EN-PTFE and EN-MoS₂ coatings in terms of friction coefficient and wear resistance. PTFE and MoS₂ contents of the EN-PTFE-MoS₂ coating were increased by changing the specimen orientation from vertical to horizontal configuration, which leads to enhancement in tribological properties of the coating. After heat treatment, the wear rate of EN matrix composite coating decreased with corresponding change in phase structure.     

Enhanced tribological properties of Y/MoS2 composite coatings prepared by chemical vapor deposition

Chemical vapor deposition (CVD) is an efficient approach to prepare coatings on complex cutting tools. However, MoS₂ with self-lubrication ability and excellent tribological properties fabricated by CVD have been rarely reported in literature. The aim of this study was to deposit pure MoS₂ coatings and yttrium (Y) doped MoS₂ (Y/MoS₂) composite coatings on cemented carbide blades coated with titanium nitride by CVD. The structural and mechanical properties of the coatings were examined by scanning electron microscopy (SEM) and nanoindentation, respectively. The results demonstrated that the microstructure of Y/MoS₂ composite coatings was denser than that of the pure MoS₂ coating. The hardness and the adhesional properties were significantly enhanced for the Y/MoS₂ composite coatings. The tribological performance of the as-deposited coatings were investigated under atmospheric environment. Y/MoS₂ compostite coatings demonstrated an enhanced tribological performance with a stable and low coefficient of friction (COF) over the entire sliding time. In contrast, the COF of pure MoS₂ coating dramatically increased to value above 0.3 after a sliding time of only 30 min. Additionally, the Y/MoS₂ composite coatings showed a decreased wear rate (8.36 ± 0.29 × 10⁻⁷ mm³/Nm) compared to the pure MoS₂ coatings (3.41 ± 0.48 × 10⁻⁵ mm³/Nm) thus reflecting an improvement by two order of magnitude.     

Wear and corrosion properties of electroless nickel composite coatings with PTFE and/or MoS2 particles

This study focuses on the effect of co-deposition of PTFE and/or MoS₂ particles on the morphology, wear, and corrosion properties of electroless nickel coating. The composite coating of EN–PTFE–MoS₂ was heat treated at different temperatures for hardness investigations. The surface morphology of coatings was characterized by scanning electron microscopy. Pin-on-disk and potentiodynamic polarization tests were used to study the tribological and corrosion properties of the coatings, respectively. Results of hardness analysis revealed that the hardness of electroless nickel coatings was increased by the heat treatment, and its maximum was gained at 400°C. Wear investigations showed that simultaneous co-deposition of the PTFE and MoS₂ particles into the nickel coating increased the wear resistance of the coating by about 30% and reduced the average value of friction coefficient to 0.25 from 0.65. Corrosion studies illustrated that simultaneous co-deposition of the PTFE and MoS₂ particles led to reduction in corrosion resistance by 10 and 5 times that of EN coating in brine and acidic solution, respectively.     

Mechanical and tribological properties of polyoxymethylene modified with nanoparticles and solid lubricants

Polyoxymethylene (POM) composites modified with nanoparticles, polytetrafluoroethylene (PTFE) and MoS₂ were prepared by a twin‐screw extruder. The effect of nanoparticles and solid lubricant PTFE/MoS₂ on mechanical and tribological properties of the composites were studied. Tribological tests were conducted on an Amsler friction and wear tester using a block‐on‐ring arrangement under dry sliding and oil lubricated conditions, respectively. The results showed that generally speaking POM nanocomposites had better stiffness and tribological properties than corresponding POM composites attributed to the high surface energy of nanoparticles, except that the tensile strength of three composites and dry‐sliding tribological properties of POM/3%Al₂O₃ nanocomposite decreased due to the agglomeration of nanoparticles. Tribological properties differed under dry sliding and oil lubricated conditions. The friction coefficient and wear volume of POM nanocomposites under oil lubricated condition decreased significantly. The increased deformation resistance supported the increased wear resistance of POM nanocomposites. POM/PTFE/MoS₂/3%Al₂O₃ nanocomposite had the best mechanical and tribological properties of all three composites, which was attributed to the synergistic effect of nanoparticles and PTFE/MoS₂. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Tribological properties of polyimide coatings filled with PTFE and surface‐modified nano‐Si3N4

Polyimide (PI) coatings filled with PTFE and nano‐Si₃N₄ were prepared by a spraying technique and successive curing. Nano‐Si₃N₄ particles were modified by grafting 3‐aminopropyltriethoxysilane to improve their dispersion in the as‐prepared coatings. Friction and wear performances and wear mechanisms of the coatings were evaluated. The results show that the incorporations of PTFE and modified nano‐Si₃N₄ particles greatly improve the friction reduction and wear resistance of PI coating. The friction and wear performance of the composite coating is significantly affected by the filler mass fraction and sliding conditions. PI coating incorporated with 20 wt % PTFE and 5 wt % modified nano‐Si₃N₄ displays the best tribological properties. Its wear rate is more than one order of magnitude lower and its friction coefficient is over two times smaller than that of the unfilled PI coating. Differences in the friction and wear behaviors of the hybrid coatings as a function of filler or sliding condition are attributed to the filler dispersion, the characteristic of transfer film formed on the counterpart ball and the wear mechanism of the coating under different sliding conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40410.     

Tribological behavior of the polyamide composite coating filled with different fillers under dry sliding

The polyamide (PA) composite coating filled with the particles of microsized MoS₂, microsized graphite, and nano‐Al₂O₃, respectively, were prepared by flame spraying. The friction and wear characteristics of the PA coating and composite coating filled with the varied content of filler under dry sliding against stainless steel were comparatively investigated using a block‐ring tester. The morphologies of the worn surfaces and transfer films on the counterpart steel ring were observed on a scanning electron microscope. The result showed that the addition of fillers to the composite coatings changed significantly the friction coefficient and wear rate of the coatings. The composite coatings filled with a low level content of fillers showed lower wear rate than did pure PA coating under dry sliding; especially the MoS₂/PA composite coating had the lowest wear rate among these composite coatings. The composite coatings with a high level content of fillers had higher wear rate than did pure PA coating, except of the Al₂O₃/PA composite coating. The bonding strengths between the polymer matrix and fillers changed with the content of the fillers, which accounted for the differences in the tribological properties of the composite coatings filled with the varied content fillers. On the other hand, the difference in the friction and wear behaviors of the composite coatings and pure coating were attributed to the difference in their worn surface morphologies and transfer film characteristics. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

YSZ/MoS2 self-lubricating coating fabricated by thermal spraying and hydrothermal reaction

Thermal sprayed ceramic coatings have extensively been used in components to protect them against friction and wear. However, the poor lubricating ability severely limits their application. Herein, yttria-stabilized zirconia (YSZ)/MoS₂ composite coatings were successfully fabricated on steel substrate with the combination of thermal spraying technology and hydrothermal reaction. Results show that the synthetic MoS₂ powders are composed of numbers of ultra-thin sheets (about 7 ~ 8?nm), and the sheet has obvious lamellar structure. After vacuum impregnation and hydrothermal reaction, numbers of MoS₂ powders, look like flowers, generate inside the plasma sprayed YSZ coating. Moreover, the growing point of the MoS₂ flower is the intrinsic micro-pores of YSZ coating. The friction and wear tests under high vacuum environment indicate that the composite coating has an extremely long lifetime (>?100,000 cycles) and possesses a low friction coefficient less than 0.1, which is lower by about 0.15 times than that of YSZ coating. Meanwhile, the composite shows an extremely low wear rate (2.30?×?10^?7 mm³ N^?1 m^?1) and causes slight wear damage to the counterpart. The excellent lubricant and wear-resistant ability are attributed to the formation of MoS₂ transfer films and the ultra-smooth of the worn surfaces of hybrid coatings.     

Comparison of structure and tribological properties of MoS2-Ti films deposited by biased-dc and pulsed-dc

A closed field unbalanced magnetron sputter (Teer-CFUBMS/550) system was used for the deposition of MoS₂-Ti composite coatings on steel substrate (AISI D2) using biased-dc and pulsed-dc. The tribological properties of MoS₂-Ti coatings were characterized by pin-on-disc wear tester under atmospheric conditions. Structural analysis was pointed out using X-ray diffraction and SEM-EDS. The microstructure and chemical composition of MoS₂-Ti films are very strongly influenced by the sputtering process conditions. While X-ray diffraction pattern of films deposited using pulsed-dc shows mainly (0 0 2) reflections, the films deposited by dc-bias exhibit random orientation being both (0 0 2) and (1 0 0) reflections. Tribological performance of the films deposited using both techniques were compared in view of both crystallographic orientation and Ti content.     

Study on the Friction and Wear Behaviors of Modified PA66 Composites

The wear-resistant polyamide 66 (PA66) composites were prepared and the mechanical properties, friction and wear properties were inspected. Results show that GF, PTFE and MoS₂ can improve the mechanical, friction and wear properties of PA66 composites. PTFE is more effective on the friction and wear properties than MoS₂ when GF is 30%wt. The best effect of the modification is 35%wt GF when both PTFE and MoS₂ were added. Friction coefficient first increase, then reduce to be stable as sliding time increases. Friction coefficient and wear mass loss increase as load increases. The main wear mechanisms are fatigue and abrasion wears.     

Effect of MoS2 content on friction and wear properties of Mo and S co-doped CrN coatings at 25–600 °C

With increasingly harsh working environments for mechanical systems and the rapid development of various high-tech industries, requirements for the stable operation of mechanical systems are increasing in a wide temperature range. Mo and S co-doped CrN coatings with different MoS₂ contents were prepared via unbalanced magnetron sputtering to provide better friction properties to the coatings at high temperatures. Scanning electron microscopy and nanoindentation were adopted to analyze the microstructure and mechanical performance. The mechanical performance of the coatings was enhanced by increasing the MoS₂ content, however, excessive MoS₂ reduced the mechanical properties of the coatings. Besides, the adhesion of the coatings first increased and then decreased rapidly with the increase of the MoS₂ content. In addition, the residual stress of the coating first decreased and then increased upon increasing the MoS₂ content. The high-temperature tribological behavior of the coatings was measured from room temperature (25 °C) to 600 °C. The CrN/MoS₂-0.6A coating was found to exhibit low friction and wear coefficient at room temperature and relatively good comprehensive properties at high temperature. This study provides a feasible design for engineering applications and lays the foundations for the preparation of coatings with superior high-temperature friction properties.     

Effect of Annealing Temperature and Alumina Particles on Mechanical and Tribological Properties of Ni-P-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Composite Coatings

In this study, the effect of annealing temperature and alumina particles on micro-hardness, corrosion, wear, and friction of Ni-P-Al₂O₃ composites coating is studied. The electroless nickel composite coating with various alumina particle content is deposited on a mild steel substrate. The corrosion behaviour and tribological behaviour (wear and friction) of the composite coated samples are investigated and compared with Ni-P coated samples. The micro-hardness, wear resistance, and corrosion resistance of the composite coating improved significantly after heat treatment (400 °C) and in the presence of alumina particles. The composite coating deposited with alumina particle concentration of 10 g/L in an electroless bath and heat treated at 400 °C shows excellent results compared to Ni-P, as-deposited Ni-P-Al₂O₃ coating and coatings heat treated at different annealing temperature (200 °C, 300 °C, and 500 °C). Microstructure changes and composition of the composite coatings due to incorporation of alumina particles and heat treatment are studied with the help of SEM (scanning electron microscopy), EDX (energy dispersive X-ray analysis and XRD (X-ray diffraction analysis).     

Synergistic effect of surface textures and DLC coatings for enhancing friction and wear performances of Si3N4/TiC ceramic

To enhance the tribological properties of Si₃N₄ based ceramics, surface textures of dimples combined with DLC coatings are fabricated on Si₃N₄/TiC ceramic surface by nanosecond laser and plasma enhanced chemical vapor deposition (PECVD). The dry friction and wear performances are evaluated by unidirectional sliding friction tests using a rotary ball-on-disk tribometer. Results reveal that the friction and wear properties of Si₃N₄/TiC ceramics are significantly enhanced by DLC coatings or dimpled textures, and the DLC coatings combined with dimpled textures show the best efficiency in reducing friction, adhesion and wear. This improvement can be explained by the synergistic effect of DLC coatings and surface textures, and the synergistic mechanisms are attributed to the formation of lubrication film and secondary lubrication, debris capture of dimpled textures, increased surface hardness and mechanical interlocking effect, and reduced contact area.     

Enhancement of mechanical and tribological properties in ring‐opening metathesis polymerization functionalized molybdenum disulfide/polydicyclopentadiene nanocomposites

This study focuses on the possibility of improving performance properties of polydicyclopentadiene (PDCPD) nanocomposites for engineering applications using nanoparticles. In this article, molybdenum disulfide/polydicyclopentadiene (MoS₂/PDCPD) nanocomposites have been prepared by in situ ring‐opening metathesis polymerization using reaction injecting molding (RIM) process. To enhance the interfacial adhesion between the fillers and PDCPD matrix, the surface modified MoS₂ nanoparticles hybridized with dialkyldithiophosphate (PyDDP) were successfully prepared by in situ surface grafting method. The effect of low MoS₂ loadings (<3 wt %) on the mechanical and tribological behaviors of PDCPD was evaluated. The results indicated that the friction coefficient of the MoS₂/PDCPD nanocomposites was obviously decreased and the wear resistance of nanocomposites was greatly improved by the addition of PyDDP‐hybridized MoS₂ nanoparticles; meanwhile, the mechanical properties were also enhanced. The MoS₂/PDCPD nanocomposites filled with 1 wt % PyDDP‐hybridized MoS₂ exhibited the best mechanical and anti‐wear properties. The friction coefficient was shown to decrease by more than 40% compared to pure PDCPD by incorporating just 1 wt % hybridized MoS₂ nanoparticles, and modest increase in modulus and strength was also observed. The reinforcing and wear‐resistant mechanisms of MoS₂/PDCPD nanocomposites were investigated and discussed by scanning electron microscopy. The well interfacial compatibility between the particle/matrix interfaces played an important role for the improved mechanical and tribological properties of MoS₂/PDCPD nanocomposites in very low MoS₂ loadings. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Ni-P-PTFE自润滑镀层的耐磨性能及其增强机理研究

采用化学复合镀技术将纳米聚四氟乙烯(PTFE)微粒沉积到化学镀Ni-P镀层中。扫描电镜(SEM)表明:镀层内PTFE微粒分散均匀,与Ni-P镀层结合紧密。摩擦磨损实验表明:在100N作用下,Ni-P-PTFE镀层的摩擦因数约为0.03,具有良好的摩擦学性能。热处理后的摩擦磨损实验表明:经热处理后,镀层仍具有较低的摩擦因数和良好的耐磨性能。     

Tribological properties of porous PPS/PTFE composite filled with mesopore titanium oxide whisker

Nano‐micro hierarchical porous polyphenylene sulfide/polytetrafluoroethylene (PPS/PTFE) composites were prepared by mold‐leaching and vacuum melting process under high temperature condition. The tribological behaviors of porous PPS/PTFE composites and the synergism as a result of incorporation of both micro‐porogen (NaCl) and mesoporous TiO₂ whiskers were investigated. The effects of mesoporous TiO₂ whiskers and nonperforated TiO₂ whiskers on the friction and wear properties of PPS/PTFE composites were comparatively studied, respectively. Results indicated that the wear rate of porous PPS/PTFE composites with 30 wt % NaCl and 7 wt % mesoporous TiO₂ whiskers obtained the lowest values under the load of 100 N. Compared with pure PPS, the wear resistance of nano‐micro porous PPS/PTFE composite was enhanced by 6.45 × 10³ times, showing outstanding wear resistance. During sliding condition, grease could be squeezed through the nano‐micro pores under the coupling effect of load and friction heat, and formed a lubricanting layer on friction surface, providing self‐lubricating effect and high wear resistance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Microstructure,thermal, physico–mechanical and tribological characteristics of molybdenum disulphide‐filled polyamide 66/carbon black composites

With an objective to investigate the influence of molybdenum disulphide (MoS₂) on physico–mechanical and tribological properties of polyamide 66 (PA 66), was compounded with MoS₂ in the presence of carbon black (CB). The compounded material was injection molded to make test specimens to evaluate physico–mechanical, thermal, and tribological (wear, friction, and laser etching) characteristics. It was found that tensile strength, percentage elongation at break, and tensile modulus of PA 66/CB/MoS₂ composite increased linearly with increase in MoS₂ content. The impact strength of the PA 66 matrix increased from 37.2 to 43.2 J/m with an increase in MoS₂ content. The wear behavior of PA 66/CB/MoS₂ composites have been investigated under dry sliding conditions at different normal loads, sliding distances, and sliding velocities at room temperature. It was found that the introduction of MoS₂ in the presence of CB has certainly reduced the friction, wear behavior of PA 66 with improvement in laser etching resistance. MoS₂ could increase the adhesion between the transfer film and the counterface surface. The ability of the synergistic fillers in helping the formation of thin, uniform, and continuous transfer film would contribute to enhance the wear resistance of PA 66 composites. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Tribological performance of DLC-coated ceramics against cemented carbide under dry sliding conditions

In order to improve the tribological behavior of Si₃N₄/TiC ceramics, DLC coating was fabricated on the ceramic surface through magnetron sputtering technology. The surface and cross-section micrographs, the adhesion between coating and substrate, the surface roughness and microhardness of the DLC-coated ceramics were investigated. Reciprocating friction tests sliding against cemented carbide ball were conducted under dry sliding conditions. The test results indicated that the DLC coating possessed superior tribological performance, which was conductive to decreasing the friction coefficient and enhancing the wear resistance of ceramics. The primary mechanisms responsible for performance improvement of the DLC-coated ceramics were attributed to the combined effects of low shear stress, excellent adhesion with substrate, high microhardness and good surface roughness. It was believed that the DLC coating was efficient in improving the load-carrying capacity and expanding the application area of ceramic materials.     

Tribological properties of the polyacrylate/PTFE coating modified by POSS in the space environment

The irradiation conditions in the low earth orbit (LEO) severely inhibit the development of polymeric materials for solid lubrication coatings used on the external surfaces of spacecraft. To solve the problem, octavinyl polyhedral oligomeric silsesquioxanes (OvPOSS) were covalently grafted onto poly(methyl/butyl methacrylate) composites (PMB). The results showed that the appropriate incorporation of OvPOSS (10 wt %) significantly reduced the friction coefficient and improved the wear resistance of the OvPOSS/PMB composite coatings. Furthermore, the impact of OvPOSS on the tribological properties of PMB/polytetrafluoroethylene (PTFE) lubrication coatings in the space environment was investigated. In particular, the degradations, mass losses, surface morphologies, and chemical compositions of POSS/PMB/PTEF composite coatings were characterized under ultraviolet (UV), electric irradiation (EI), and atomic oxygen (AO). The results indicated that OvPOSS provides numerous Si O Si bonds in the polymer matrix that improve the resistance to UV and EI. Besides, a passivating SiO₂ layer was formed to prevent further erosion and degradation of the underlying PMB and PTFE components during AO irradiation. Particularly, the wear resistance of OvPOSS/PMB/PTFE coatings under AO irradiation increased significantly compared with the pristine PMB/PTFE coating. Overall, our results indicate that POSS-containing composites are a good prospective material for space application in the LEO. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48730.