Enhancement Of Tribological Performance Research Articles

Tribological studies of epoxy and its composite coatings on steel in dry and lubricated sliding

Industrial lubricants are invariably used with additives (with high sulfur and phosphorous contents) for tribological performance enhancement. However, these additives are environmentally very harmful. Hence, there is an urgent need to find alternate solutions for enhancing the tribological performance of lubricants and components without the use of harmful additives. The objective of this work is to investigate the feasibility of using polymer composite coatings in enhancing the tribological properties of steel surfaces in dry and base oil lubricated conditions. Pure epoxy and its composite (with 10 wt-% of graphene or graphite powder) films were coated onto steel substrates and tested under dry and base oil lubricated conditions. Friction and wear experiments were conducted on a ball on cylinder tribometer between polymer/composite coated cylindrical steel surface (shaft) and an uncoated steel ball as the counterface. Tests were conducted at various normal loads and speeds. In dry condition at 3 N load and 0.63 m s− 1 sliding speed, the wear life of epoxy was increased by five times and coefficient of friction was nearly the same (0.18) on inclusion of graphene nanoparticle. In lubricated case, epoxy/graphene composite coating performed eight times and more than five times better than pure epoxy and epoxy/graphite respectively.

Surface Modified UHMWPE Particles by Direct Fluorination Blended with Polyurethane for Enhancing its Wear-Resistant Performance

In this study, Ultra-high molecular weight polyethylene (UHMWPE) particles were surface treated by F2/N2 and F2/O2/N2 two direct fluorination routes. A great number of polar groups are grafted on the surface of UHMWPE particles after direct fluorination confirmed by FT-IR and X-ray photoelectron spectroscopy (XPS) characterization. Two kinds of surface modified UHMWPE particles were blended with thermoplastic polyurethane (TPU) by dissolving in solvent. The scanning electron microscope (SEM) demonstrates that the interfacial interaction degree between the two polymer phases is correlated with the chemical composition of a fluorinated surface layer. The TPU composite with the UHMWPE particle treated by F2/O2/N2 route obtains excellent tribological performance enhancement with significant decrease in wear loss, ranging from 192.9 mm3 to 97.8 mm3, about 49.3% reduction compared with the virgin TPU.

The wear-resistance of composite depending on the interfacial interaction between thermoplastic polyurethane and fluorinated UHMWPE particles with or without oxygen

Abstract Ultra-high-molecular-weight polyethylene (UHMWPE) particle surface modified by direct fluorination was used as the wear-resistant filler incorporated into thermoplastic polyurethane (TPU) to prepare the high wear-resistant composite. In this study, UHMWPE particles were surface modified by direct fluorination using fluorine–nitrogen or fluorine–oxygen–nitrogen reactive fluoride mixture. The results of ATR-FTIR and X-ray photoelectron spectroscopy indicate that a large number of polar groups are covalently bonded on the surface of UHMWPE particles after direct fluorination. Larger quantities of oxygen-containing groups on the surface layer are introduced by fluorine–oxygen–nitrogen modified process. Two kinds of surface modified UHMWPE particles were solution blended with one polyester-type TPU. The scanning electron microscope and mechanical properties of composites indicate that the interfacial interaction between the two components is dependent on the chemical structure of the fluorinated surface layer on the particles. The composite with oxy-fluorine-functionalized UHMWPE particles obtains more excellent tribological performance enhancement with significant decrease in wear loss of about 62.7% reduction in compared with virgin TPU. This composite exhibits stronger interfacial adhesion than that with UHMWPE particles only modified by fluorine–nitrogen due to more chemical bonding interaction forming between the two polymer component interfaces.

Effect of SiC particle impact nano-texturing on tribological performance of 304L stainless steel

Abstract Topographical features on sliding contact surfaces are known to have a significant impact on friction and wear. Indeed, various forms of surface texturing are being used to improve and/or control the tribological performance of sliding surfaces. In this paper, the effect of random surface texturing produced by a mechanical impact process is studied for friction and wear behavior of 304L stainless steel (SS) under dry and marginal oil lubrication. The surface processing was applied to 304L SS flat specimens and tested under reciprocating ball-on-flat sliding contact, with a 440C stainless steel ball. Under dry contact, the impact textured surface exhibited two order of magnitude lower wear than the isotropically ground surface of the same material. After 1500 s of sliding and wearing through of the processed surface layer following occurring of scuffing, the impact textured surface underwent a transition in wear and friction behavior. Under marginal oil lubrication, however, no such transition occurred, and the wear for the impact textured surface was consistently two orders of magnitude lower than that for the ground material. Mechanisms for the tribological performance enhancement are proposed.

Surface Layer Modification of 6061 Al Alloy by Friction Stir Processing and Second Phase Hard Particles for Improved Friction and Wear Performance

This paper presents the results of the study on mechanical and tribological performance enhancement of 6061 aluminum alloys by incorporation of B4C particle via friction stir processing (FSP). The incorporation of B4C particles reduced friction by 30% and reduced wear by two orders of magnitude compared to unprocessed base material. FSP alone without particles addition did not have a significant effect on the tribological behavior of the aluminum alloy studied.

Enhancement of Tribological Performance via Innovative Tooling Design for Extrusion Processes

A novel design of extrusion tooling is proposed. This process segments the traditional die set into three separate pieces, a punch, a wall die, and a bottom die. Additionally, the wall die is given the freedom to move along the axis of the punch and a high pressure lubricant is supplied to the interface between the wall and bottom dies. Preliminary tests of the segmented tooling show that, if the tribological conditions are severe enough, the forming load will decrease in comparison to a conventional extrusion system.

A composite with excellent tribological performance derived from oxy-fluorinated UHMWPE particle/polyurethane

The thermoplastic polyurethane (TPU)/UHMWPE composite with good compatibility and strong interfacial adhesion is achieved by using direct fluorination surface modification technology. The obtained composite has excellent tribological performance enhancement efficiency with significant decrease in wear volume loss and friction coefficient.

Magnetron reactively sputtered Ti-DLC coatings on HNBR rubber: The influence of substrate bias

In this study, Ti-containing diamond-like carbon (Ti-DLC) coatings have been deposited on HNBR (hydrogenated nitrile butadiene) rubber and also on Si wafer as reference via unbalanced magnetron reactive sputtering from a Ti target in C 2H 2/Ar plasma. The deposition rates of coatings on rubber and Si wafer were about the same. Columnar structures resulting from a rough interface were often observed in the coatings deposited on rubbers. Only at a high bias voltage of − 300 V the coating on HNBR rubber became column-free whereas a bias voltage of − 100 V could already restrain the columnar structure and thus produced dense and smooth coatings on Si wafer. A segmented morphology of the coatings on HNBR rubber is formed as a result of the large difference in thermal expansion between the coating and HNBR rubber. The crack network that separates the patches plays an important role in maintaining the coating flexibility. The size of the patches reduces with increasing bias voltage and thus the variation of deposition temperature. A high bias voltage enhances the hardness of Ti-coating and the rubber-coating adhesion, and guarantees a good tribological performance. When sliding against ø6 mm 100Cr6 steel ball counterpart, very low coefficients of friction were achieved (< 0.25 for the coated rubber versus > 1.3 for the uncoated). The Ti-DLC coating can be considered as a promising material for the enhancement of tribological performance of rubbers.

Effect of carbon fibers surface treatment on tribological performance of polyurethane (PU) composite coating

The carbon fibers (CF) were pre-treated in two different ways: no pre-treatment, and activation in HNO 3 plus application of toluene-2,4-diisocyanate (TDI). Carbon fibers have been introduced into polyurethane (PU) composite coatings. The tribological behaviors of the polyurethane composite coating filled with CF or TDI-modified CF (TDI-CF) were studied using a ring-on-block wear tester under dry sliding, and the worn surfaces of the filled PU coatings and transfer films formed on the surface of the counterpart ring sliding against the PU coating were investigated by SEM and optical microscope (OM), respectively. Owing to the effective improvement of the interfacial adhesion between the CF and polyurethane matrix, compared with the cases of untreated CF, the employment of low content TDI-CF provided the PU coating with much higher tribological performance enhancement efficiency. The investigations of the frictional surfaces showed that low content TDI-CF was able to enhance the adhesion of the transfer films of the PU coating to the surface of counterpart ring, so they significantly reduced the wear of the PU coating.

Effect of nano-Al2O3 surface treatment on the tribological performance of phenolic composite coating

To overcome the disadvantages generated by the loosened nano-particle agglomerates dispersed in polymer composites, a chemical grafting method was applied to modify nano-Al2O3 by covalently bonding toluene-2, 4-diisocyanate (TDI) onto the particles. The tribological behaviors of the phenolic composite coating filled with nano-Al2O3 or toluene-2, 4-diisocyanate treated Al2O3 (TDI-Al2O3) were studied using a ring-on-block wear tester under dry sliding, and the worn surfaces of the filled phenolic coating and transfer films formed on the surface of the counterpart ring sliding against the composite coating were investigated by SEM and optical microscope (OM), respectively. Owing to the effective improvement of the interfacial adhesion between the nano-Al2O3 and phenolic matrix, compared with the cases of untreated nano-Al2O3, the employment of TDI modified nano-Al2O3 (TDI-Al2O3) provided the phenolic coating with much higher tribological performance enhancement efficiency. Compared with other filled phenolic coating, 3 wt.% TDI-Al2O3 reinforced phenolic coating has the lowest frictional property and the highest wear resistance. Furthermore, we studied effect of sliding speed and applied load on the friction and wear behaviors of the phenolic coating filled with 3 wt.% nano-Al2O3 or TDI-Al2O3. The results showed that the friction coefficient of the composite coating reinforced with different fillers decreased with increasing sliding speed and applied load, and the anti-wear behavior of the coating filled with 3.0 wt.% TDI-Al2O3 was the best under 320 N and at a speed of 3.0 m/s. The investigations of the frictional surfaces showed that low content nano-Al2O3 or TDI-Al2O3 was able to enhance the adhesion of the transfer films of the phenolic coating to the surface of counterpart ring, so they significantly reduced the wear of the phenolic coating. FTIR and TGA analyses indicated that the surface of Al2O3 was coated with TDI through the covalent bond between the hydroxy groups of Al2O3 and –OCN groups of TDI.

Tribological improvements of ion implanted technological alloys: Plasma immersion vs. conventional ion implantation

This work reports a comparative investigation on tribological performance enhancement induced by nitrogen Plasma Immersion Ion Implantation (PI3) and conventional Nitrogen Ion Implantation (I2) on Ti and Al based alloys. The study has been carried out on the basis of the surface modification produced by both treatment techniques, in terms of the implanted nitrogen in-depth profiles, and its effect on surface hardening and wear resistance increase of the treated samples.Under the experimental conditions described, PI3 Ti-based alloys treated samples evidenced slightly better tribological performance than those subjected to I2 treatments. In the case of Al alloys, however, PI3 caused strong detrimental modification on the treated samples as revealed in the increase by a factor 100 of its surface roughness. Consequently, different criteria should be deemed in order to establish the adequacy of one or other technique, not only taking into account set up costs but also considering specific applications.

Effect of particle surface treatment on the tribological performance of epoxy based nanocomposites

To overcome the disadvantages generated by the loosened nanoparticle agglomerates dispersed in polymer composites, an irradiation grafting method was applied to modify nanosilica by covalently bonding polyacrylamide (PAAM) onto the particles. When the grafted nanosilica was added to epoxy, the curing kinetics of the matrix was accelerated. Moreover, the grafting PAAM can take part in the curing of epoxy so that chemical bonding was established between the nanometer fillers and the matrix. Sliding wear tests of the materials demonstrated that the frictional coefficient and the specific wear rate of nanosilica/epoxy composites are lower than those of the unfilled epoxy. With a rise in nominal load, both frictional coefficient and wear rate of the composites decrease, suggesting a wear mechanism different from that involved in wearing of epoxy. Grafted nanosilica reinforced composites have the lowest frictional property and the highest wear resistance of the examined composites. Compared with the cases of microsized silica and untreated nanosilica, the employment of grafted nanosilica provided the composites with much higher tribological performance enhancement efficiency.

Improvement of Tribological Performance of Epoxy by the Addition of Irradiation Grafted Nano-Inorganic Particles

To develop wear resistant nanocomposite coating materials, the authors of the present work treated nanosilica first by introducing a certain amount of grafting polymers onto the particles in terms of an irradiation technique. Through irradiation grafting, the nanoparticle agglomerates turn into a nanocomposite microstructure (comprised of the nanoparticles and the grafted, homopolymerized secondary polymer), which in turn built up a strong interfacial interaction with the surrounding epoxy matrix through chain entanglement and chemical bonding during the subsequent mixing and consolidation. The experimental results indicated that the addition of the grafted nanosilica into epoxy significantly reduced wear rate and frictional coefficient of the matrix at low filler loading. Compared with the cases of microsized silica and untreated nanosilica, the employment of grafted nanosilica provided composites with much higher tribological performance enhancement efficiency. Unlike the approaches for manufacturing of other types of nanocomposites, the current method is characterized by many advantages, such as simple, low cost, easy to be controlled, and broader applicability.

Improvement of Tribological Performance of Epoxy by the Addition of Irradiation Grafted Nano-Inorganic Particles

To develop wear resistant nanocomposite coating materials, the authors of the present work treated nanosilica first by introducing a certain amount of grafting polymers onto the particles in terms of an irradiation technique. Through irradiation grafting, the nanoparticle agglomerates turn into a nanocomposite microstructure (comprised of the nanoparticles and the grafted, homopolymerized secondary polymer), which in turn built up a strong interfacial interaction with the surrounding epoxy matrix through chain entanglement and chemical bonding during the subsequent mixing and consolidation. The experimental results indicated that the addition of the grafted nanosilica into epoxy significantly reduced wear rate and frictional coefficient of the matrix at low filler loading. Compared with the cases of microsized silica and untreated nanosilica, the employment of grafted nanosilica provided composites with much higher tribological performance enhancement efficiency. Unlike the approaches for manufacturing of other types of nanocomposites, the current method is characterized by many advantages, such as simple, low cost, easy to be controlled, and broader applicability.

Tribological performance enhancement of amorphous hard carbon films on AISI 52100 bearing steel

Hard carbon films synthesized on disks of hardened AISI 52100 steel by Ar + beam sputtering were simultaneously bombarded by Ne + at energy of 200 eV. Characteristics such as the surface morphology and structure, the film-substrate interface, and the hardness have been investigated. Transmission electron microscopy and Auger electron spectroscopy revealed that the films consisted of carbon atoms in an amorphous structure. Hard carbon films exhibited a smooth surface and a high microhardness of 1900 kgf mm −2. Tribological experiments on the films were performed with a ball-on-disk tribometer without lubrication in a room-temperature atmosphere, except for the experiment at 107 °C. The curves of friction coefficient and the scanning electron microscopy pictures indicated that the hard carbon films had an excellent wear resistance. The wear coefficients and antiwear numbers confirmed that, as the wear load did not surpass 10 N, the wear of the films was mild, which showed a drastic reduction in the wear compared with AISI 52100 steel without hard carbon films.