Comparative Study of Tribological Properties of Polyphenylene Sulfide (PPS), Polyethersulfone (PES), and Polysulfone (PSU)

The tribological properties of polyphenylene sulfide (PPS), polyethersulfone (PES) and polysulfone (PSU), which have similar molecular structures, were investigated using an end-face contact tribometer and a reciprocating tribometer. The thermomechanical behavior of the polymers was analyzed using dynamic mechanical analysis (DMA). PPS exhibited a maximum friction coefficient with increasing load and sliding speed, while the friction coefficients of PES and PSU decreased only slightly. The wear rate of PPS was much lower than that of PES and PSU under high loads and speeds. It is suggested that the main factors influencing the friction and wear properties of the neat polymers are their condensed state and heat resistance. Amorphous PES and PSU showed liquid-like behavior and very low friction when the frictional surface was in the molten-flow state. The macromolecular crystals of crystallizable PPS give it some solid-like behavior and load-carrying capacity; hence PPS exhibited lower wear than PES and PSU.     

Studies on wettability, mechanical and tribological properties of the polyurethane composites filled with talc

A series of polyurethane (PU)/talc composites modified by a high molecular weight hydroxyl-terminated polydimethylsiloxane (HTPDMS) were prepared. The effect of the talc content on the mechanical, wettability and tribological properties of the PU composites was studied. Tensile strength of the PU composites reached to the maximum after adding 5% talc. The water contact angles (CA) of the original surfaces and worn surfaces of the polyurethane composites were measured. The experimental results indicated that the contact angles of the worn surface increased after friction. The friction and wear experiments were tested on a MRH-3 model ring-on-block test rig at different sliding speeds and loads under dry sliding and water lubrication. Experimental results revealed that the talc contributed to largely improve the tribological properties of the PU composites. The coefficient of friction (COF) of the composites increased with increasing talc. Scanning electron microscopic (SEM) investigations showed that the worn surfaces of the talc filled PU composites were smoother than pure polyurethane under given load and sliding speed.     

Effects of Aramid Fiber and Polytetrafluoroethylene on the Mechanical and Tribological Properties of Polyimide Composites in a Vacuum

Polyimide composites filled with aramid fiber (AF) and polytetrafluoroethylene (PTFE) were prepared by hot press molding. The thermal, mechanical, and tribological properties of the composites were studied systematically. The friction and wear behavior, sliding against GCr15 steel balls, were evaluated in a ground-based wear in space simulation facility using a ball-on-disk tribosystem. The morphologies of the worn surfaces during the sliding process of the composites were analyzed by scanning electron microscopy to reveal the wear mechanism. It was found that the heat-resisting performance and the hardness of the composites were minimally affected by the additives. The flexural strength of polyimide/AF/PTFE (PI-3) decreased when PTFE was added. The wear resistance increased and the coefficient of friction decreased due to the effect of both fillers. In vacuum, the friction coefficients of polyimide (PI-1), polyimide/AF (PI-2), and PI-3 increased slightly with sliding velocity, while the opposite results were obtained in air. With the increase of air pressure the friction coefficients of the samples increased.     

Self-Lubricating Ultrahigh Molecular Weight Polyethylene Thin Films with Excellent Wear Resistance at Light Friction Loads on Glass and Silicon

Thin films of ultrahigh molecular weight polyethylene (UHMWPE) were prepared on glass and silicon using a dip-coating technique, followed by removal of the decahydronaphthalene solvent at 140?°C for 20?hours and cooling in the oven in air. The wetting ability of the films was investigated by a contact angle method. The tribological behavior of the films was investigated using a ball-on-disk configuration in reciprocating mode. The reciprocating frequency of 4?Hz and single sliding distance of 5?mm used corresponded to a sliding speed of 40?mm/s. The counterface was a GCr15 steel ball with diameter of 3?mm and the normal frictional loads were 10–300?g. The worn surfaces on the films and wear scars on the steel ball were observed and analyzed by scanning electron microscopy (SEM). It was found that the surface morphologies of the films on glass and silicon were different, which is ascribed to the difference in thermal conductivity of the glass and silicon. Evaporation of the solution caused micro-orifices in the films on glass. The water contacting angle of about 87° on the films on the two substrates was similar to that of bulk UHMWPE. Their friction coefficient of about 0.1–0.2 indicated the films were self-lubricating. The wear life of the films decreased quickly with the increase of friction load. At light friction loads, the films showed excellent wear resistance. Extrusion was believed to be the main wear mechanism of the films.     

Friction and Wear Behavior of Polyamide 66/Poly(vinylidene fluoride) Blends

The tribological performance of PA66 and PVDF blends was investigated by a block‐on ring sliding friction and wear tester. The appropriate amount of PVDF can decrease the friction coefficient and improve the wear resistance of PA66. Moreover, the appropriate amount of PA66 can improve the wear resistance of PVDF. SEM analysis shows that PVDF is noncompatible with PA66, and the blend presents a two‐phase structure. A smooth worn surface is a main reason for improving the frictional and wear properties of the PA66/PVDF blend. Besides, slight debris is an important factor in improving the wear resistance of the PA66/PVDF blend. FT‐IR analysis shows that the oxidation and degradation behavior of PVDF is effectively controlled in the PA66/PVDF blends. Therefore, the blend of PA66 and PVDF is a potential polymer material for tribological applications.     

Friction and wear of rare earths modified carbon fibers filled PTFE composite under dry sliding condition

Carbon fibers (CF) were surface treated with air-oxidation and rare earths (RE), respectively. The friction and wear properties of polytetrafluoroethylene (PTFE) composites filled with differently surface treated carbon fibers, sliding against GCr15 steel under dry sliding condition, were investigated on a block-on-ring M-2000 tribometer. Experimental results revealed that RE treatment largely reduced the friction and wear of CF reinforced PTFE (CF/PTFE) composites. The RE treated composite exhibited the lowest friction and wear under dry sliding. Scanning electron microscopy (SEM) investigation of worn surfaces and transfer films of CF/PTFE composites showed that RE treated CF/PTFE composites had the smoothest worn surface under given load and sliding speed, and a continuous and uniform transfer film formed on the counterface. X-ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that the oxygen concentration was obviously increased after RE treatment, and more carboxyl groups were introduced onto CF surfaces after RE treatment. The increase in the amount of oxygen-containing groups increased the interfacial adhesion between CF and PTFE matrix, and accordingly increased the tribological properties of the composite.     

Ultraviolet or Atomic Oxygen Effects on Tribological Properties of the Carbon Fibers/Polyimide Composites

Carbon fibers-reinforced polyimide composites (CF-PI) were fabricated by means of a hot press molding technique. To contrast the effects of ultraviolet and atomic oxygen irradiation under high vacuum on the tribological properties of CF-PI composites, the friction and wear properties of the composites sliding against GCr15 steel ball before and after irradiation were conducted in high vacuum on a ball-on-disk test rig. The experimental results revealed that CF-PI composites exhibited higher modulus and lower coefficient of friction and worn rate value than pure polyimide under high vacuum. However, the coefficient of friction of composites increased and the worn rate value decreased after ultraviolet or atomic oxygen irradiation, which slightly affected the tribological properties of CF-PI composites. The chemical composition of the composites changed after irradiation was inspected by X-ray photoelectron spectroscopy. Microstructure of the worn surfaces of the tested composites was investigated by scanning electron microscopy to reveal the wear mechanism.     

Tribological Behavior of Fluorinated and Nonfluorinated Polyimide Films

In this study a series of polyimide (PI) films were synthesized from fluorinated and nonfluorinated monomers which contained diamines and dianhydrides. The influence of fluorine-containing groups on the glass transition temperature (T _g) and tribological properties of the PI films was investigated. The wear mechanism for the different kinds of PI polymers was comparatively discussed. T _g was characterized by dynamic mechanical analysis and the tribological changes were evaluated by friction and wear tests as well as scanning electron microscopy (SEM) analysis of the worn surfaces. Fourier transform infrared (FTIR) has been used to study the structures of the PI polymers. Experimental results indicated that the fluorine groups influenced the thermal behavior (T _g) of the PI films. Nonfluorinated PI films have lower friction coefficient and wear rate compared with the fluorinated ones. It was also found that the tribological properties of the PI films were closely related with the applied load. The friction coefficients and wear rates reduced with increasing the applied load.     

Tribological behaviors of lanthanum-based phosphonate 3-aminopropyltriethoxysilane self-assembled films

Lanthanum-based thin films deposited on the phosphonate 3-aminopropyltriethoxysilane (APTES) self-assembled monolayer (SAM) were prepared on the hydroxylated glass substrate by a self-assembling process from specially formulated solution. Chemical compositions of the films and chemical state of the elements were detected by X-ray photoelectron spectrometry (XPS). The thickness of the films was determined with an ellipsometer, while the morphologies of the original and worn surfaces of the samples were analyzed by means of atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively. The tribological properties of the films sliding against GCr15 steel ball were evaluated on a UMT-2MT reciprocating friction and wear tester. As the results, the target film was obtained and reaction may have taken place between the film and the glass substrate. The tribological results show that lanthanum-based thin films are superior in reducing friction and resisting wear compared with APTES-SAM and phosphorylated APTES-SAM. SEM observation of the morphologies of worn surfaces indicates that the wear of APTES-SAM and the phosphorylated APTES-SAM is characteristic of brittle fracture and severe abrasion. Differently, slight abrasion and micro-crack dominate the wear of lanthanum-based thin films. The superior friction reduction and wear resistance of lanthanum-based thin films are attributed to the enhanced load-carrying capacity of the inorganic lanthanum particles in the lanthanum-based thin films as well as good adhesion of the films to the substrate.     

Tribological Properties of Hydroxyl-Terminated Liquid Nitrile Rubber-Modified Polyurethane/Epoxy Interpenetrating Polymer Network Composites

A series of castor oil-based polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites modified by two kinds of hydroxy-terminated liquid nitrile rubber (HTLN) was prepared. A systematic investigation of the tribological properties of the two kinds of HTLN-modified PU/EP IPN composites was carried out through a pin-on-disk arrangement under dry sliding conditions. Experimental results revealed that the incorporation of HTLN can improve the friction and wear properties of PU/EP IPN significantly. Both the friction coefficient and wear loss decreased with increasing content of HTLN. The worn surfaces of the samples were analyzed using scanning electron microscope and a three-dimensional (3D) noncontact surface-mapping profiler; the results showed that the worn surfaces of the PU/EP IPN composites became smooth when the HTLN was added. The mechanisms for the improvement of tribological properties are discussed.     

Development and characterization of alkali treated abaca fiber reinforced friction composites

Abaca fibers show tremendous potential as reinforcing components in composite materials. The purpose of this study is to investigate the effect of abaca fiber content on physical, mechanical and tribological properties of abaca fiber reinforced friction composites. The friction composites were fabricated by a compression molder and investigated using a friction test machine. The experiment results show that surface treatment of abaca fibers could improve the mechanical properties of abaca fiber and interface bonding strength of the abaca fiber and composite matrix. Density of friction composites decreased with the increasing of abaca fiber content (0 wt%–4 wt%). The different content of abaca fibers had less effect on hardness of specimens, whereas large of impact strength. The specimen F3 with 3 wt% abaca fibers had the lowest wear rate and possessed the best wear resistance, followed by specimen F4 with 4 wt% abaca fibers. The worn surface morphologies were observed using the Scanning Electron Microscopy for study the tribological behavior and wear mechanism. The results show that a large amount of secondary contact plateaus presented on the worn surface of specimen F3 which had relatively smooth worn surface.     

Tribological aspects in nanostructuring burnishing of structural steels

The paper studies tribological aspects of nanostructuring burnishing of steels. The efficiency of the process in improving the tribological properties of steels is assessed as regards the choice of an indenter material and lubricant-coolant reasoning from the friction coefficient at the “indenter-treated part” contact and from the absence of adhesive bond and fatigue microcracks. It is shown that synthetic diamond and dense boron nitride are promising indenter materials for nanostructuring burnishing of corrosion-resistant 20X13 steel and cement 20X steel. It is demonstrated that nanostructuring burnishing increases the wear resistance of structural steels under abrasive action and sliding friction in different media (lubricant, water, air, and argon) due to suppressed processes of microcutting, plastic edging, fatigue and oxidation wear, and adhesive bonding.     

The Mechanical and Tribological Properties of Aramid (Twaron) Fabric/Polytetrafluoroethylene Composites

A series of composites with Twaron fabric as reinforcement and polytetrafluoroethylene (PTFE) as matrix were fabricated with various contents of PTFE, viz. 30, 40, 50, 60, and 70 vol%. The Rockwell hardness and tensile strength of the composites were tested according to the corresponding standards. The composites were also evaluated for their tribological behaviors on an MPX-2000A friction and wear tester. The worn surface and wear debris of the composites were observed by scanning electron microscopy (SEM) and the mechanism is discussed. The PTFE content in the composites had a great influence on both the mechanical and tribological properties. The composite with 40 vol% PTFE provided the proper wetting of the fibers and the best load transfer efficiency and, hence, showed the best mechanical properties and tribological behaviors.     

Mechanical and Tribological Properties of Self-Reinforced Polyphenylene Sulfide Composites

25%, 50%, and 75% polyphenylene sulfide (PPS) long fiber reinforced PPS resin were prepared by a hot pressing method. Neat resin PPS and PPS fiber samples were also prepared to compare with the self-reinforced PPS composites. The reinforcing fibers were preheat treated at 240°C for 24 h. The tribological properties of the self-reinforced PPS composites against an AISI 1045 steel ring were determined by a block on ring type friction tester. Differential scanning calorimetry (DSC) results indicated that a higher degree of crystallinity was retained in the self-reinforced PPS composites than in neat PPS resin after hot pressing. Therefore, the addition of PPS fiber improved both the mechanical and tribological properties of PPS resin significantly. Dynamic mechanical analysis (DMA) demonstrated that the PPS fibers increased the glass transition temperature (Tg) of the PPS resin. SEM images of the fracture surfaces indicated that the toughness of the samples increased with increasing PPS fiber content. Additionally, PPS fibers improved the tribological properties of PPS resin by significantly reducing the friction coefficient and wear rate.     

Tribological Properties of Poly(Para-Phenylene Sulfide) and its Carbon Fiber Composites with Water Lubrication

Tribological properties of poly(para-phenylene sulfide) (PPS) with different molecular mass were studied. PPS properties were compared with the same properties of its carbon fiber-filled plastics. For the interpretation of tribological test results an especial role was assigned to the load capacity of materials. The concept of load capacity permits consideration of different tribological dependencies as phase diagrams. The structure of the samples was characterized by X-ray diffraction and differential scanning calorimetry techniques.     

Friction and Wear Behaviors of Surface-Modified Carbon Fabric/Epoxy Resin Composites

Carbon fabric (CF) was pretreated by air-plasma bombardment and then further modified by deposition of polydopamine on the surface of the pretreated CF. Epoxy resin composites reinforced by unmodified or surface-modified carbon fabric were fabricated. The friction and wear behaviors of the resulting composites were evaluated in a ring-on-block contact mode. The flexural strength and Rockwell hardness of the composites were also evaluated. The morphologies of the worn surfaces of the unmodified and modified composites were analyzed by scanning electron microscopy. The surface treatment increased the surface roughness and changed the surface topography of the CF, which contributed to enhancing the interfacial adhesion of the composites and thus improved the mechanical properties and tribo-performance. The friction and wear properties of both the unfilled and filled composites were highly dependent on the load and sliding velocity. Moreover, the results were supplemented with scanning electron micrographs to help understand the possible wear mechanisms.     

Synthesis and tribological properties of AA5052-base insitu composites

Abstract

It is important to optimize the properties of a material for a particular application, hence, to find the suitable material for tribological applications, the wear and friction behaviour of AA5052 in situ composites with different kind of reinforcements have been investigated. For present study, three in situ formed composites have been produced with different reinforcements namely Al₃Zr, ZrB₂ and combination of both (Al₃Zr + ZrB₂) by direct melt reaction (DMR) technique. The as-cast composites and base alloy have been characterized by X-ray diffraction (XRD), optical microscopy, electron microscopy, tensile testing, hardness and dry sliding wear and friction tests. XRD results indicate the successful formation of second phase reinforcement particles in all composites. Wear test results indicate that the cumulative volume loss increases with an increase in sliding distance while coefficient of friction shows a fluctuating tendency, whereas with increasing applied load, wear rate shows an increasing trend while coefficient of friction shows decreasing trend. The variation of wear rate with composites indicates that the composite with multiple reinforcement (Al₃Zr + ZrB₂) has lowest wear rate among all as-cast composites and base alloy, while coefficient of friction is higher. The responsible mechanisms concerned with wear and friction results have been discussed in detail with the help of the observation on worn surface analysis by scanning electron microscope (SEM) and 3D-profilometer. All tribological results have been correlated with the microstructural properties, strength parameters and bulk hardness of the composites.     

Characterization and tribological investigation of SiO2 and La2O3 sol–gel films

Thin films of SiO₂ and La₂O₃ were prepared on a glass substrate by a dip-coating process from specially formulated sols. The tribological properties of the resulting thin films sliding against a Si₃N₄ ball were evaluated on a one-way reciprocating friction and wear tester. The morphologies of the unworn and worn surfaces of the films were examined by an atomic force microscope (AFM) and a scanning electron microscope (SEM). La₂O₃ shows the best tribological performance. The coefficient of friction is about 0.1 and the wear life is over 5000 sliding passes both under higher (3 N) and lower load (1 N). The SiO₂ film derived from a specially formulated aqueous solution shows much better performance in resisting wear and reducing friction than the one derived from an ethanol solution. The wear mechanisms of the films are discussed based on SEM observation of the worn surface morphologies. SEM observation of the morphologies of worn surfaces indicates that the worn surface of La₂O₃ is too slight to be observed by SEM. The wear of SiO₂ derived from TEOS solution is the characteristic of delaminating, which is responsible for the abrupt failure of the film. The wear of SiO₂ derived from aqueous solution is the characteristic of fracture. Brittle fracture and severe abrasion dominate the wear of glass substrate.     

Tribological behaviors of self-assembled 3-aminopropyltriethoxysilane films on silicon

3-Aminopropyltriethoxysilane (APTES) thin films were prepared on the hydroxylated silicon substrate by a self-assembling process from formulated solution. Chemical compositions of the films were detected by X-ray photoelectron spectrometry (XPS). The thickness of the films was determined with an ellipsometer, while the morphologies of the original and worn surfaces of the samples were analyzed by means of atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively. The tribological properties of APTES thin films sliding against GCr15 steel ball were evaluated on a UMT-2MT reciprocating friction and wear tester. It was found that the macroscopic friction coefficients for coating times more than 1 h ranged from 0.177 to 0.3 whereas the value for short coating time was as high as 0.8. It was also found that the tribological behaviors of APTES films were sensitive to normal load and sliding velocity. SEM observation of the morphologies of worn surfaces indicates that the wear of silicon is characteristic of brittle fracture and severe abrasion. Differently, abrasion and micro-crack dominate the wear of APTES–SAM. The superior friction reduction and wear resistance of APTES films compared to the silicon substrate are attributed to good adhesion of the films to the substrate.     

Study on the Tribological Properties of Carbon Fabric Reinforced Phenolic Composites Filled with Nano-Al2O3

Carbon fabric reinforced phenolic (CFRP) composites filled with nano-Al₂O₃ were prepared by a dip-coating and heat molding process and the tribological properties of the resulting composites under different sliding conditions were investigated systematically on a block-on-ring test rig. The worn surfaces were observed in a scanning electron microscope (SEM) to understand the mechanism. Nano-Al₂O₃ particles, as the filler, were effective in reducing the friction coefficient and wear rate of the CFRP composites. The steady state friction coefficient of the CFRP composites filled with 4 wt.% nano-Al₂O₃ particles was about 65.5% of that of unfilled CFRP composites, and the wear rate, in this case, was about 74.7% of that of unfilled CFRP composites. Tribological tests under different sliding conditions revealed that the filled CFRP composites seemed to be more suitable than unfilled CFRP composites for tribological applications under higher sliding speed and load. Moreover, the wear resistances of the unfilled and filled CFRP composites were found to be related to the stability of the transfer film on the counterface.