Influence of functional graphene as filler on the tribological behaviors of Nomex fabric/phenolic composite

Graphene and polystyrene functionalized graphene (PS-graphene) had been synthesized, and were employed as fillers to improve the anti-wear property and load-carrying capacity of Nomex fabric/phenolic composites. Pin-on-disk type wear tests show that the friction coefficients and wear rates for both graphene and PS-graphene filled fabric/phenolic composites were reduced, when compared with unfilled fabric composite. Moreover, it was found that the 2 wt% PS-graphene filled Nomex fabric/phenolic composites exhibited the optimal tribological properties. The enhancement on the wear property of graphene and PS-graphene filled Nomex fabric composite was mainly due to the self-lubrication of graphene and the easy-formed transfer film on the counterpart pin. We also investigated the effect of filler content, applied load, and sliding speed on the tribological properties of the Nomex fabric/phenolic composites.     

Enhanced wear resistance of hybrid PTFE/Kevlar fabric/phenolic composite by cryogenic treatment

Hybrid PTFE/Kevlar fabric was treated by cryogenic approach. The untreated or cryo-treated fabric was incorporated into fabric/phenolic composite for friction and wear tests. It was found that the wear resistance of the fabric/phenolic composite was improved after cryo-treatment, although the friction coefficient increased to a certain extent. SEM observations showed that the roughness of hybrid fabric increased by cryo-treatment, which may enhance the mechanical interlocking of the phenolic resin on the fiber surface. Enhanced fiber/resin adhesion was considered to contribute to the improved wear resistance of cryo-treated fabric/phenolic composite.     

Effect of sillimanite particle reinforcement on dry sliding wear behaviour of aluminium alloy composite

Abstract

The effect of sillimanite reinforcement on the dry sliding wear behaviour of aluminium silicon alloy (BS LM6) composite was investigated using a pin-on-disc sliding wear test machine. The composite specimens were prepared using the liquid metallurgy technique and 10 wt-% of sillimanite particles were incorporated in the matrix alloy. Sliding wear tests were conducted at applied pressures between 0.2 and 1.6 MPa and speeds of 1.89, 3.96 and 5.55 m s^-1. The matrix alloy was also prepared and tested under identical conditions in order to enable comparison. It was observed that the sillimanite reinforced composite exhibited a lower wear rate than the matrix alloy. Increase in applied load increased the wear rate while increase in speed exhibited the reverse effect. The seizure pressure of the composite was significantly higher than that of the matrix alloy. The temperature rise near the contacting surface and the coefficient of friction were less in the composite than in the matrix alloy. SEM micrographs of the worn surface and subsurface were used to predict the nature of the wear mechanism.     

Influence of copper and molybdenum on dry sliding wear behaviour of sintered plain carbon steel

Study of wear behaviour of sintered low alloy steels is required to ascertain their applications for wear resistance. In the present work the influence of copper and molybdenum on wear behaviour of plain carbon steel (Fe–0.5%C) using pin-on-disk arrangement has been addressed. Atomized iron (Fe), graphite (C), copper (Cu) and molybdenum (Mo) elemental powders were suitably weighed and thoroughly mixed in a pot mill to yield the alloy powders of Fe–0.5%C, Fe–0.5%C–2%Cu and Fe–0.5%C–2%Mo. Admixed alloy powders were then compacted and sintered for obtaining preforms of aspect ratio (height/diameter) 1.3 and diameter 25 mm. The sintered preforms were then hot extruded and subsequently machined to obtain wear test specimens of diameter 6 mm and height 50 mm. Using Design of Experiment software, the sliding wear experiments were planned and conducted on a pin-on-disk tribometer. It has been found that there is a substantial improvement in wear resistance of the P/M plain carbon steel by the addition Mo rather than Cu. However coefficient of friction is higher due to presence of hard microstructural phases. Delamination wear is found predominant for both the alloy steels. Empirical correlations for mass loss and coefficient of friction with respect to load/speed have been developed for the alloy steels.     

Dry sliding wear behavior of heat treated hybrid metal matrix composite using Taguchi techniques

Dry sliding wear behavior of zinc based alloy and composite reinforced with SiCp (9 wt%) and Gr (3 wt%) fabricated by stir casting method was investigated. Heat treatment (HT) and aging of the specimen were carried out, followed by water quenching. Wear behavior was evaluated using pin on disc apparatus. Taguchi technique was used to estimate the parameters affecting the wear significantly. The effect of HT was that it reduced the microcracks, residual stresses and improved the distribution of microconstituents. The influence of various parameters like applied load, sliding speed and sliding distance on wear behavior was investigated by means and analysis of variance (ANOVA). Further, correlation between the parameters was determined by multiple linear regression equation for each response. It was observed that the applied load significantly influenced the wear volume loss (WVL), followed by sliding speed implying that increase in either applied load or sliding speed increases the WVL. Whereas for composites, sliding distance showed a negative influence on wear indicating that increase in sliding distance reduces WVL due to the presence of reinforcements. The wear mechanism of the worn out specimen was analyzed using scanning electron microscopy. The analysis shows that the formation and retention of ceramic mixed mechanical layer (CMML) plays a major role in the dry sliding wear resistance.     

Effect of inter-ply sliding on the quality of multilayer interlock dry fabric preforms

Forming thick, complex shapes with several layers is needed in high technology fields. During forming, defects can occur and have to be taken into account because they can significantly affect the mechanical performance of the part. This experimental study shows that, when working with dry fabric forming, the type and number of defects is a function of the punch geometry, the process parameters, the orientation of the fabric with respect to the punch and the inter-ply friction. Inter-ply friction has a huge effect on the quality of the preform when inter-ply sliding occurs. This inter-ply friction leads to several overhanging yarn shocks that generate high tangential forces, which inhibit the relative sliding of plies. In addition, to reduce the number and amplitude of defects, the layers subjected to severe defects can be placed in the inner position where they are subjected to the compression applied by the upper layers.     

Changes to near-surface region of PTFE during dry sliding against steel

PTFE specimens were slid against an EN24 disc. The unworn and worn surfaces as well as the wear debris were examined by X-ray diffraction. Sliding was found to introduce (i) shrinkage of the unit cell, (ii) enlargement of crystallites and (iii) residual stresses in the slid PTFE surface. No conformational changes in the 15₇ helix could be observed due to sliding. The wear debris was found to be 1 m thick warped laminates.     

Research on thermal properties of Nomex/Viscose FR fibre blended fabric

Thermal properties of fabrics made of Nomex 462 and Lenzing Viscose FR (Flame-retardant) fibres were analysed. After vertical burning, Limiting Oxygen Index (LOI) and Thermal Gravity (TG) tests it was discovered that the blended material compared favorable with the 100% Nomex goods in thermal behaviours. Among the seven fabric groups with various ratios of the two components, Sample No. 6 with the blended ratio of 80/20 (Nomex/Lenzing Viscose FR) demonstrated excellent thermal properties, in which case the LOI value was the highest and damaged length in vertical burning test the shortest. By blending Nomex and Viscose FR filaments to produce flameproof fabric may be an economical choice because of the lower price of the later component.     

Mechanical and sliding wear properties of multi-layered laminates from glass fabric/graphite/epoxy composites

Multi-layered laminates of bi-directionally woven E-glass fabric/epoxy with different loading of graphite particles were made by hand layup followed by compression molding. Tensile and flexural behaviors, impact strength, hardness and density of these laminates were determined. Wear behaviors of these composites were investigated by a pin-on-disc wear test apparatus. Specific wear rates of these composites strongly depend on their filler content and applied normal loads. The hybrid composite containing 3 wt% of graphite exhibits the optimum mechanical and wear performances. A further increase in the graphite content increases the specific wear rate and deteriorates the mechanical behavior. The lowest (σ e)⁻¹ factor (the reciprocal of the product of tensile strength and elongation at break) signifies the lowest specific wear rate. The results of the morphology study of the wear test specimens support the results of the wear test.     

Friction and wear of Synfluo 180XF wax and nano-Al2O3 filled Nomex fabric composites

Nomex fabric composites filled with the particulates of Synfluo 180XF wax (SFW) and nano-Al₂O₃ was prepared by dip-coating of Nomex fabric in a phenolic resin containing particulates to be incorporated and the successive curing. The friction and wear performance of the pure and filled Nomex fabric composites sliding against AISI-1045 steel in a pin-on-disk configuration were evaluated on a Xuanwu-III high temperature friction and wear tester. The microstructure of the composites, and the morphologies of the worn surfaces and the morphologies of counterpart steel pins were analyzed by means of scanning electron microscopy. And the elemental plane distribution of Al on the cross-section of the Nomex fabric composites filled with nano-Al₂O₃ was analyzed with an energy dispersive X-ray analyzer (EDAX). The results showed that the addition of Synfluo 180XF wax in composites have the potential to increase wear resistance and friction reduction of Nomex fabric composites, and the addition of the nano-Al₂O₃ with the optimum mass fraction in composites can improve the anti-wear ability of the composites. Besides the self-properties of the filler, the character of the microstructure of the Nomex fabric composites filled with different particles, coupled with the character of the transfer film, largely accounts for the improved anti-wear and friction-reducing abilities of the filled Nomex fabric composites as compared with the unfilled one.     

银-二硫化钼复合材料滑动电磨损机理的研究

采用粉末冶金方法制备银-二硫化钼复合材料,研究了材料在滑动电磨损状态下的摩擦系数、磨损量和接触电压降变化情况,探讨了电磨损发生过程的机理.研究表明:与纯机械磨损相比,电磨损过程中材料的摩擦系数差别不大;在电磨损过程中发生阳极侵蚀现象,材料从阳极向阴极发生转移,正刷的磨损量大于负刷,纯机械磨损量在二者之间;磨损过程中由于正刷侧的二硫化钼膜厚度大于负刷,以及正刷微观导电点的数量少于负刷,使得正刷的接触电压降高于负刷.     

Friction and wear behaviors of B4C/6061Al composite

The friction and wear behaviors of B₄C/6061Al composite were studied by considering the effect of sliding time, applied load, sliding velocity and heat treatment. The results show that, when the sliding time, applied load and sliding velocity reach critical values (namely 120 min, 30 N and 240 r min⁻¹, respectively), the mass loss and friction coefficient (COF) increase significantly. Severe delamination wear is the main wear mechanism after sliding for 120 min and under an applied load of 30 N. While fretting wear happens at a sliding velocity of 240 r min⁻¹. After solution-treated at 550 °C for 1 h and then aged at 180 °C for 15 h, the composite shows the highest wear resistance owing to the precipitation of β″ (Mg₂Si) phases in the matrix and the strong interface bonding between B₄C particles and the matrix alloy.     

Influence of reinforcement volume fraction on sliding wear behaviour of SHS derived ferrous based metal matrix composite

Abstract

Steel matrix composites reinforced with (W,Ti)C particles were processed by directaddition of an innovative powder to molten 0.4 wt-%Clow alloy steel.Thispowder was producedusing a self-propagatinghightemperature synthesis(SHS) reaction and consisted of a dispersion of fine (W,Ti)C particles (5-10 μm) in an iron binder. Dry unidirectional sliding wear behaviour ofthe compositematerialanditsunreinforced counterpartwas investigated atroomtemperature against a white cast iron counterface. In situ monitoring of wear and friction, in conjunction with electron microscopy, has been used tointerpretwearscar microstructures observed intermsofwear mechanisms. Wear experimentswere performedat a sliding speed of 1.5 m s^-1 at different test loads. It was found that the wear resistance of the composite material was superior to that of their unreinforced counterparts over the entire range of loading employed during this investigation. The unreinforced base alloy exhibited a transition from mild to severe wear at a load of approximately 70 N. No such transition was found to occur for the composite materials. Instead, after a transient period of running in wear, steady state conditions were observed. At the highest level of carbide addition this transient period did not occur and the composite wore in a regime of mild wear over the full spectrum of loading utilised.     

Effect of sliding condition and wear surface state on the tribological behaviour of SiCp/Cu composite

Abstract

The present work was undertaken to investigate the effect of sliding condition and wear surface state on the dry sliding wear behaviour of SiC_p/Cu composite. Three kinds of sliding conditions, namely continuous sliding, interrupted sliding, and interrupted and cleaning sliding were employed. It was observed that a compact mechanically mixed layer (MML) was present on the worn surface of the composite, which effectively decreased the wear loss of the sliding pair. The new running in period of the interrupted tests led to breakage of the MML. Sufficient sliding and entrapment of wear debris in the contact region were two important preconditions for the formation of an MML. Therefore, continuous sliding or long period sliding is favoured to extend the life of this dry tribosystem.     

Sliding wear performance of metallic laser coatings against composite PTFE seals

Laser coatings are frequently used in applications where they slide against various elastomeric and polymeric seals or guide bands in different environments. Examples of such applications include hydraulics, maritime propulsion systems and components in pulp & paper industry. In this study highly corrosion resistant Inconel 625 (DIN Mat. No. 2.4856) and Thermanit 2509 super duplex stainless steel (～1.4501) coatings manufactured by novel coaxial hot‐wire laser cladding technique are tested in dry conditions at room temperature against various composite polytetrafluoroethylene (PTFE) seals. Despite only small difference in coating surface hardness, ～1.4501 and 2.4856 show significant differences in wear and friction performance against various seals. For instance, ～1.4501 is superior to 2.4856 against glass fiber and MoS₂ reinforced PTFE in terms of wear resistance and friction characteristics, whereas 2.4856 performs better against bronze reinforced PTFE seal. The reference Stellite laser coating, which is the hardest counter surface in this study, exhibits the best wear behavior against all the seal materials tested. The differences in wear performances are explained by cohesive and adhesive wear mechanisms.     

Interlaminar fracture properties of weft-knitted/woven fabric interply hybrid composite materials

An experimental study has been undertaken to characterize the delamination behavior and tensile properties of interply hybrid laminated composites reinforced by interlock weft-knitted and woven glass fiber preform fabrics. The hybrid composites, comprising the alternate layers of interlock and uniweave fabrics, were compared to interlock knitted (only) and uniweave (only) composites with respect to delamination and tensile performances. Mode-I double cantilever beam and mode-II end-notched flexure tests were carried out to assess the interlaminar fracture toughness using aluminum-strip stiffened specimens. The mode-I and mode-II interlaminar fracture toughness values, G _IC and G _IIC, for the hybrid composite were about three and two times higher than that for the uniweave composite, respectively. The tensile strength and modulus of the hybrid composite were 315 MPa and 12.8 GPa in the wale direction, respectively, demonstrating that the strength and modulus were found to be slightly lower than those of the uniweave composite, and significantly improved in comparison with the interlock knitted composites.     

Microstructure and dry sliding wear behavior of hot-extruded AlSiCuPb bearing alloys

The microstructures, mechanical properties and dry wear behavior of hot-extruded AlSiCuPb bearing alloys have been studied. It showed that the hot-extruded AlSiCuPb alloys possessed microstructures with uniformly distributed lead particles and fine broken grains of silicon, and exhibited further improved mechanical properties in comparison to the stir cast ones. With increasing the lead content, the wear rate decreased greatly and wear rate-load curves took different form for extruded bearing alloys containing 20% and 25% lead. Optical observation revealed the reason was formation of a black compact film of lubricant covering almost the entire worn surface of specimens at highly applied load level. This film is a mixture of different constituents containing the elements Al, Si, O, Fe and Pb.