Effect of MoS2/PTFE coatings on performance of Si3N4/TiC ceramics in dry sliding against WC/Co

To enhance the tribological performance of Si₃N₄/TiC ceramics, MoS₂/PTFE composite coatings were deposited on the ceramic substrate through spraying method. The micrographs and basic properties of the MoS₂/PTFE coated samples were investigated. Dry sliding friction experiments against WC/Co ball were performed with the coated ceramics and traditional ones. These results showed that the composite coatings could significantly reduce the friction coefficient of ceramics, and protect the substrate from adhesion wear. The primary tribological mechanisms of the coated ceramics were abrasive wear, coating spalling and delamination, and the tribological property was transited from slight wear to serious wear with the increase of load because of the lower surface hardness and shear strength. The possible mechanisms for the effects of MoS₂/PTFE composite coatings on the friction performance of ceramics were discussed.     

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.     

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.     

Friction and wear characteristics of ceramic particle filled polytetrafluoroethylene composites under oil-lubricated conditions

Five kinds of polytetrafluoroethylene (PTFE)-based composites were prepared: PTFE, PTFE + 30 vol % SiC, PTFE + 30 vol % Si₃N₄, PTFE + 30 vol % BN, and PTFE + 30 vol % B₂O₃. The friction and wear properties of these ceramic particle filled PTFE composites sliding against GCr15 bearing steel under both dry and liquid paraffin lubricated conditions were studied by using an MHK-500 ring-block wear tester. The worn surfaces and the transfer films formed on the surface of the GCr15 bearing steel of these PTFE composites were investigated by using a scanning electron microscope (SEM)and an optical microscope, respectively. The experimental results show that the ceramic particles of SiC, Si₃N₄, BN, and B₂O₃ can greatly reduce the wear of the PTFE composites; the wear-reducing action of Si₃N₄ is the most effective, that of SiC is the next most effective, then the BN, and that of B₂O₃ is the worst. We found that B₂O₃ reduces the friction coefficient of the PTFE composite but SiC, Si₃N₄, and BN increase the friction coefficients of the PTFE composites. However, the friction and wear properties of the ceramic particle filled PTFE composites can be greatly improved by lubrication with liquid paraffin, and the friction coefficients of the PTFE composites can be decreased by 1 order of magnitude. Under lubrication of liquid paraffin the friction coefficients of these ceramic particle filled PTFE composites decrease with an increase of load, but the wear of the PTFE composites increases with a load increase. The variations of the friction coefficients with load for these ceramic particle filled PTFE composites under lubrication of liquid paraffin can be properly described by the relationship between the friction coefficient (μ) and the simplified Sommerfeld variable N/P as given here. The investigations of the frictional surfaces show that the ceramic particles SiC, Si₃N₄, BN, and B₂O₃ enhance the adhesion of the transfer films of the PTFE composites to the surface of GCr15 bearing steel, so they greatly reduce the wear of the PTFE composites. However, the transfer of the PTFE composites onto the surface of the GCr15 bearing steel can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. Meanwhile, the interactions between the liquid paraffin and the PTFE composites, especially the absorption of liquid paraffin into the surface layers of the PTFE composites, create some cracks on the worn surfaces of the ceramic particle filled PTFE composites; the creation and development of these cracks reduces the load-supporting capacity of the PTFE composites. This leads to the deterioration of the friction and wear properties of the PTFE composites under higher loads in liquid paraffin lubrication. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2611–2619, 1999     

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).     

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.     

Ni-P复合镀层摩擦磨损性能的研究

采用化学复合镀在碳钢基体上共沉积（Ni-P）-SiC和（Ni-P）-PTFE两种复合镀层,重点研究了两种复合镀层在相同对磨条件下的摩擦磨损性能及磨损机理表现形式,并与化学镀镍磷层进行对比。结果表明,本实验条件下所制备的（Ni-P）-SiC和（Ni-P）-PTFE两类复合镀层分别具有优异的耐磨和减磨性能,均能对所镀覆基体材料起到良好的保护作用;对磨实验过程中主要出现磨料磨损、粘着磨损和氧化磨损三种磨损方式,而且磨损方式不同,镀层的摩擦磨损性能表现也不尽相同。     

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 behaviour of TiB2-HfC ceramic tool material under dry sliding condition

In order to disclose friction and wear mechanism of TiB₂-HfC ceramic, tribological behaviour of TiB₂-HfC ceramic sliding against YG8, 316 stainless steel (316) and TA2 were investigated. Friction coefficients between TiB₂-HfC ceramics and these materials decreased not only with an increase of sliding speed but also with an increase of normal load, respectively. Wear rates of TiB₂-HfC ceramics sliding against these materials increased with an increase of sliding speed as well as with an increase of normal load, respectively. B₂O₃, TiO₂ and HfO₂ formed in TiB₂-HfC ceramics sliding against these materials. In addition, intergranular and transgranular microcracks and WO₃ appeared in the worn surface after the ceramic slid against YG8; lamellar structures like fish scale, areas of exposed grains, pits, Fe_xO_y and Cr₂O₃ existed in the worn surface after the ceramic slid against 316; ribbon-like structures, areas of exposed grains, wear particles and furrows existed in the worn surface after the ceramic slid against TA2. Besides oxidation wear, abrasive wear played an important role in TiB₂-HfC ceramic sliding against YG8, while adhesive wear and abrasive wear played a dominant role in TiB₂-HfC ceramic sliding against 316 or TA2.     

Wear properties and microstructures of alumina matrix composite ceramics used for drawing dies

The alumina matrix ceramics used for drawing dies were prepared by hot-press sintering method. The ceramics materials were made of Al₂O₃/TiC, Al₂O₃/(W,Ti)C and Al₂O₃/Ti(C,N). Mechanical and friction properties of these materials were tested and measured. The experiments for testing friction properties were carried on wear and tear machine. Mechanisms of frictions were analyzed with scanning electron microscope. Results showed that the alumina matrix composite ceramics have good physical and mechanical properties for used as drawing dies. Measured friction coefficients of alumina matrix composite ceramics showed a trend of decline and kept the value of 0.4–0.5 with the rotating speed of 550 rpm. Alumina matrix composite ceramics have smaller wear rate, while the wear rates of Al₂O₃/TiC and Al₂O₃/(W,Ti)C decrease gradually with a rising rotation speed. The wear of alumina matrix ceramics was severe at deformation zone. The primary wear behaviors of alumina matrix ceramics are scraping and furrowing. Even though the mechanisms for wear different, abrasive and adhesive wear were found to be the predominant wear mechanisms for the ceramic drawing die.     

Applicability of DLC and WC/C low friction coatings on Al2O3/TiCN mixed ceramic cutting tools for dry machining of hardened 52100 steel

The present work examines the applicability of DLC and WC/C low friction coatings on Al₂O₃/TiCN based mixed ceramic cutting tools for the dry and hard turning of AISI 52100 steel (62 HRC). The characterization of coated tools reveals that the coatings retain very low values of surface roughness, whereas the DLC coating exhibits much higher microhardness when compared to the WC/C coating. On the other hand, the WC/C coating exhibit a coarse surface morphology virtually due to the tungsten doping. Later, continuous turning tests were executed with the help of coated and uncoated cutting tools under dry cutting conditions, and their performance was investigated in terms of machining forces, cutting temperature and tool wear. Coating delamination by flaking and peeling is quite prominent in the case of both the coatings; however, it is less severe for the WC/C coated tool. The coatings help to reduce machining forces, cutting temperatures and tool wear, but the performance of coated tools converge towards uncoated tool as the cutting speed, and feed rate is increased. Both the coatings prevent the development of cracks near the cutting edge with WC/C coating exhibiting superior wear behavior basically due to its multilayered structure and better thermal stability. Moreover, the tested low friction coatings don't serve as thermal barriers and only the lubrication generated due to graphitization at the chip-tool interface is mostly responsible for the improved machining performance.     

Tribological properties and cutting performance of boron and silicon doped diamond films on Co-cemented tungsten carbide inserts

Boron and silicon doped diamond films are deposited on the cobalt cemented tungsten carbide (WC-Co) substrate by using a bias-enhanced hot filament chemical vapor deposition (HFCVD) apparatus. Acetone, hydrogen gas, trimethyl borate (C₃H₉BO₃) and tetraethoxysilane (C₈H₂₀O₄Si) are used as source materials. The tribological properties of boron-doped (B-doped), silicon-doped (Si-doped) diamond films are examined by using a ball-on-plate type rotating tribometer with silicon nitride ceramic as the counterpart in ambient air. To evaluate the cutting performance, comparative cutting tests are conducted using as-received WC-Co, undoped and doped diamond coated inserts, with high silicon aluminum alloy materials as the workpiece. Friction tests suggest that the Si-doped diamond films present the lowest friction coefficient and wear rate among all tested diamond films because of its diamond grain refinement effect. The B-doped diamond films exhibit a larger grain size and a rougher surface but a lower friction coefficient than that of undoped ones. The average friction coefficient of Si-doped, B-doped and undoped diamond films in stable regime is 0.143, 0.193 and 0.233, respectively. The cutting results demonstrate that boron doping can improve the wear resistance of diamond films and the adhesive strength of diamond films to the substrates. Si-doped diamond coated inserts show relatively poor cutting performance than undoped ones due to its thinner film thickness. B-doped and Si-doped diamond films may have tremendous potential for mechanical application.     

Effect of self-developed graphene lubricant on tribological behaviour of silicon carbide/silicon nitride interface

The research presented in this paper aims to investigate the effectiveness of different surface roughness and lubrication conditions on the interfacial tribological properties between silicon carbide (SiC) and silicon nitride (Si₃N₄) ceramics, particularly for providing insight into the mechanisms of how graphene reduces the friction and wear rate. The worn groove topography and surface composition were characterised in detail with 3D laser measuring microscopy and X-ray photoelectron spectroscopy. The tribological test results on the UMT-TriboLab show that a smooth initial surface is more likely to obtain a low friction coefficient and wear rate under water lubrication. The proper initial surface roughness for SiC and Si₃N₄ ceramics is approximately Ra 10?nm, and it will be lower in an alcohol or graphene aqueous solution. A large load does not worsen the tribological behaviour of a Si₃N₄ ball sliding against a SiC disk, and it reduces the friction coefficient and wear rate. Among the five lubrication states of dry friction, dry graphene lubrication, water lubrication, graphene solution lubrication, and self-developed graphene lubrication, the self-developed graphene lubricant can exhibit an ultra-low friction coefficient of 0.009 and ultra-low wear rate of 1.69?×?10^?7?mm³/N·m. The excellent tribological property of the graphene-coated ceramic surface helps the prepared lubricant to decrease the friction coefficient effectively. Furthermore, the graphene film can protect the SiC from being oxidised by water under the tribo-activated action, and therefore, lead to ultra-low wear rate under low friction condition. Alcohol improves the tribological property of the self-developed graphene lubricant, mainly because of the good wettability between graphene and ethanol. The self-developed graphene lubricant can be applied in water-lubricated ceramic bearings and motorised precision spindles.     

Tribological behavior of carbon nanotube and polytetrafluoroethylene filled polyimide composites under different lubricated conditions

The friction and wear behavior of polyimide (PI) composites reinforced with carbon nanotube (CNT) and polytetrafluoroethylene (PTFE) were comparatively evaluated under dry sliding, water‐, oil‐ or alkali‐lubricated condition. The wear mechanisms of the composites were also discussed. Results indicate that, when comparison with the dry friction situation, PI‐based composites results lower friction coefficients and wear rates under oil‐ or alkali‐lubricated condition. The lowest wear rate of the CNT/PTFE/PI composite is recorded as 1.2 × 10⁻⁶ mm³/Nm during the composite sliding in alkali, which is only about 40% of the value sliding under dry friction condition. The worn surface of neat PI under dry sliding is characterized by severe adhesive wear, whereas abrasive wear is the main character for CNT/PTFE/PI composites. The worn surfaces of CNT/PTFE/PI composites sliding in oil or alkali lubricated condition are smoother than those under dry or water condition. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Microstructure and tribological behavior of Ti3C2Tx MXene reinforced chemically bonded silicate ceramic coatings

MXenes – In recent decades, great attention has been paid to the fast-growing two-dimensional (2D) transition metal carbides and nitrides, in terms of their prominent mechanical and electrical properties. The tribological essence of MXene has not yet been entirely investigated, although researches on MXene were conducted in all aspects of its applications. Hence, a newly compound 2D MXene (Ti₃C₂T_x) is exploited to reinforce the wear resistance of the chemically bonded silicate ceramic coatings, which are utilized to protect component surfaces under severe conditions. The structural features, hardness, and tribological behaviors of the targeted coatings are investigated and analyzed. Results show that the micro-hardness of the coatings increases to 156.9 HV_0.5 when added 1.2 wt% MXene. The increment of microhardness extraordinarily reaches 33.3%, compared with the original. The coating with 1.2 wt% MXene also indicates a 31.6% decrement of the coefficient of friction (COF) and a 73% reduction of the wear rate respectively. Furthermore, fatigue is found to be the main reason of the wear mechanism, through exploring the surface morphologies of wear traces and counterpart balls.     

Repair of spline shaft by laser-cladding coarse TiC reinforced Ni-based coating: Process,microstructure and properties

To repair the surface defects of spline shaft and improve wear resistance, the coarse TiC reinforced Ni-based composite coatings were fabricated on the spline shaft surface by laser cladding with six types of precursors containing Ni45, coarse TiC, and fine TiN powder. The effects of ceramic content and fine TiN addition on the formability, microstructure, and mechanical properties of the coatings were studied comprehensively. In TiC reinforced Ni-based coatings 1–3 without fine TiN addition, the porosity decreased from 20.415 % to 0.571 % with the increase of TiC concentration. The coatings mainly consist of CrB, Cr7C3, Cr23C6, coarse TiC, and γ-Ni. With the addition of fine TiN, the length of the ceramic phases in coatings 1#–3# decreased slightly, while volume fraction and porosity increased. Moreover, the ring-shaped Ti (C, N) phases were also detected at the edges of both undissolved TiC and TiN particles, which improved the bonding force between ceramics and matrix. Besides, these ceramics inhibited the generation of columnar crystals and eliminated the heat-affected zone. The performance test results show that the coating 3# with 30 wt% TiC and 6 wt% TiN exhibits the best wear resistance despite slightly decreased hardness, and its friction coefficient of 0.409 and wear rate of 42.44 × 10⁻⁶ mm³ N⁻¹·m⁻¹ are, respectively, 0.667 and 0.307 times those of the substrate. Based on the additive/subtractive hybrid manufacturing technology, the optimized coatings were ground to obtain the finishing surface, which indicates that the coarse TiC reinforced coating can be employed in repairing the damaged parts.     

Friction and wear characteristics of PTFE composites filled with metal oxides under lubrication by oil

Four kinds of polytetrafluoroethylene(PTFE)-based composites, such as pure PTFE, PTFE+30%(v)PbO, PTFE+30%(v)Pb₃O₄, and PTFE+30%(v)Cu₂O composite, were prepared. The friction and wear properties of these metal oxides filled PTFE composites sliding against GCr15 bearing steel in both dry and lubricated conditions were studied by using an MHK-500 ring-block wear tester. Then the worn surfaces of these PTFE composites and the transfer films of these PTFE composites formed on the surface of GCr15 bearing steel were examined by using a Scanning Electron Microscope (SEM) and an Optical Microscope, respectively. Experimental results show that the friction and wear properties of these metal oxide-filled PTFE composites can be greatly improved by liquid paraffin lubrication, and the friction coefficients can be decreased by one order of magnitude. Meanwhile, the interactions between liquid paraffin and metal oxide-filled PTFE composites, especially the absorption of liquid paraffin into the surface layers of these PTFE composites, reduce the mechanical strength and the load-carrying capacity of these metal oxide-filled PTFE composites. This leads to the deterioration of the friction and wear properties of these PTFE composites. Investigations of the frictional surfaces show that Pb₃O₄, Cu₂O, and PbO enhance the adhesion of the transfer films to the surface of GCr15-bearing steel, and thus promote the transfer of the PTFE composites onto the surface of GCr15-bearing steel. Therefore, they greatly reduce the wear of the PTFE composites. However, the transfer of these PTFE composites onto the counterfaces can be greatly reduced by lubrication with liquid paraffin. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 85–93, 1997     

Hard machining performance of PVD AlCrN coated Al2O3/TiCN ceramic inserts as a function of thin film thickness

In the present work, AlCrN coating was deposited on Al₂O₃/TiCN ceramic inserts with varying thin film thickness using physical vapor deposition (PVD) technique. The thickness, surface morphology, chemical composition, hardness and adhesion strength of the coating to the substrate were characterized by field-emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), micro-indentations and scratch tests respectively. The machining performance of uncoated and coated tools was investigated in hard turning of AISI 52100 steel (62 HRC) under dry environment. The cutting behavior was analyzed in terms of machining forces, tool temperature, wear, friction and chip morphology. Further, a 3D finite element model with hybrid friction criterion has been adopted to support the experimental findings. The results revealed that coating/substrate adhesion and edge radius were the deciding criteria for the machining performance of coated tools with 3 µm coating thickness tool exhibiting best turning performance on Al₂O₃/TiCN mixed ceramic insert.     

Friction and wear characteristics of copper and its compound-filled PTFE composites under oil-lubricated conditions

Four kinds of polytetrafluoroethylene (PTFE)-based composites, such as pure PTFE, PTFE + 30(v)%Cu, PTFE + 30(v)%Cu₂O, and PTFE + 30(v)%CuS composite, were prepared. Then the friction and wear properties of the PTFE composites filled with Cu, Cu₂O, or CuS sliding against GCr15-bearing steel under both dry and liquid paraffin-lubricated conditions were studied by using an MHK-500 ring-block wear tester. Finally, the worn surfaces and the transfer films of these PTFE composites formed on the surface of GCr15-bearing steel were investigated by using a scanning electron microscope (SEM) and an optical microscope, respectively. Experimental results show that the antiwear properties of these PTFE composites can be greatly improved by filling Cu, Cu₂O, or CuS to PTFE, and the wear of these PTFE composites can be decreased by two orders of magnitude compared to that of pure PTFE under dry friction conditions. Meanwhile, CuS increases the friction coefficient of the PTFE composite, but Cu and Cu₂O reduce the friction coefficients of the PTFE composites. However, the friction and wear properties of Cu, Cu₂O, or CuS-filled PTFE composites can be greatly improved by lubrication with liquid paraffin. The friction coefficients of these PTFE composites can be decreased by one order of magnitude compared to those under dry friction conditions, while the wear of these PTFE composites can be decreased by one to two orders of magnitude. The PTFE + 30(v)%Cu composite exhibits excellent friction and wear-reducing properties under higher loads in liquid paraffin-lubricated conditions, so the PTFE + 30(v)%Cu composite is much more suitable for application under oil-lubricated conditions in practice. Optical microscope investigation of transfer films shows that Cu, Cu₂O, and CuS enhance the adhesion of the transfer films to the surface of GCr15-bearing steel, so they greatly reduce the wear of the PTFE composites. However, the transfer of the PTFE composites onto the surface of GCr15-bearing steel can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. SEM examination of worn surfaces shows that the interaction between liquid paraffin and the PTFE composites, especially the absorption of liquid paraffin into the surface layers of the PTFE composites, creates some cracks on the worn surfaces of Cu₂O or CuS-filled PTFE composites, the creation and development of the cracks reduces the load-carrying capacity of the PTFE composites; this leads to the deterioration of the friction and wear properties of the PTFE composites under higher loads in liquid paraffin lubrication. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1455–1464, 1998     

Microstructural,mechanical and tribological properties of suspension plasma sprayed YSZ/h-BN composite coating

Brittleness, relative high friction coefficient and wear rate limit the applications of ceramic coatings as wear-resistant layers. However, because embedding additives with ceramic matrix has demonstrated to be an effective way to improve coating performances, different contents and size of h-BN were added into an YSZ suspension. Afterwards, the YSZ/h-BN composite coatings were manufactured by suspension plasma spray and their tribological analysis indicated that: i) the reduction of the friction coefficient and wear rate can be achieved by incorporating h-BN into YSZ coating. ii) finer h-BN particle is more helpful to enhance the tribological properties of the coating. iii) the optimum content is dependent on h-BN particle sizes. iv) when the contents and the size of the h-BN inclusion increase, the probability distribution of the micro-hardness can become bi-modal. Three worn surface conditions were summarized and their wear mechanisms were discussed as well.