Effect of fiber orientation on friction and wear of fiber reinforced polymeric composites

The friction and wear behavior of composites (i.e. uniaxially oriented graphite fiber-epoxy, Kevlar fiber-epoxy and biaxially oriented glass fiber-MoS₂-polytetrafluoroethylene (PTFE)) was investigated as a function of varying fiber orientations with respect to the sliding direction. In graphite fiber-epoxy composites, both wear and friction coefficients were minimum when the orientation of the fibers was normal to the sliding surface. In Kevlar-epoxy composites when the fibers were oriented normal to the surface and the sliding direction, the wear rate was also minimum but the friction coefficient was the highest. In glass fiber-MoS₂-PTFE composites wear was minimum when the largest fraction of fibers was oriented normal to the sliding surface.     

Investigation on solid particle erosion behaviour of polyetherimide and its composites

The present investigation reports about, the solid particle erosion behaviour of randomly oriented short E-glass, carbon fibre and solid lubricants (PTFE, graphite, MoS₂) filled polyetherimide (PEI) composites. The erosion rates (ERs) of these composites have been evaluated at different impingement angles (15–90°) and impact velocities (30–88 m/s). Mechanical properties such as tensile strength (S), ultimate elongation to fracture (e), hardness (H_V), Izod impact strength (I) and shear strength (S_s) seems to be controlling the erosion rate of PEI and its composites. Polyetherimide and its glass, carbon fibre reinforced composites showed semi-ductile erosion behaviour with peak erosion rate at 60° impingement angle. However, glass fibre reinforced PEI composite filled with solid lubricants showed peak erosion rate at 60° impingement angle for impact velocities of 30 and 88 m/s, whereas for intermediate velocities (52 and 60 m/s) peak erosion rate observed at 30° impingement angle. It is observed that 20% (w/w) glass fibre reinforcement helps in improving erosive wear resistance of neat PEI matrix. Erosion efficiency (η) values (0.23–8.2%) indicate micro-ploughing and micro-cutting dominant wear mechanisms. The morphology of eroded surfaces was examined by using scanning electron microscopy (SEM). Possible erosion mechanisms are discussed.     

Influence of impingement angle on solid particle erosion of carbon fabric reinforced polyetherimide composite

Polyetherimide (PEI) composite reinforced with plain weave carbon fabric (CF) (40% by volume) was developed and characterized for physical and mechanical properties. The erosive wear behaviour of PEI and its composite was evaluated using silica sand particles at a constant impact velocity but varying angles of impingement. It was confirmed that though all the mechanical properties of PEI improved substantially by CF reinforcement, the erosion resistance (W_R) deteriorated by a factor of almost four–six times at all angles of impingement. Both materials showed minimum wear at normal incidence (90° impingement). In spite of the fact that PEI is not a very ductile polymer (elongation to break-60%), it showed maximum wear at 15° which is a characteristic of ductile and semi-ductile mode of failure. The composite (elongation to break-1%) also showed highest wear at 30° (impingement at 15° was not studied). These phenomena were explained using scanning electron micrographs of the eroded surfaces.     

Impact of stacking sequence on tribological wear performance of woven jute-glass hybrid epoxy composites

Natural fibre-reinforced plastic (FRP) composites have gained much interest because of their environment friendliness and cost-effectiveness compared to synthetic fibre-reinforced composites. The availability of natural fibre and ease of manufacturing have tempted researchers worldwide to develop a locally available low-cost fibre and study their feasibility for reinforcement purposes and to what extent they can satisfy the required specifications of well-reinforced polymer composite for tribological application. FRP composites have various applications in the automobile, aerospace and marine fields. They are applied to inlet cone, fan exit guide vanes and other parts of structures in a turbofan engine for lightening an engine. The erosion characteristics of the FRP composites are of vital importance due to the operational requirements in dusty environments. In this present work, the impact of stacking sequence on erosion wear behaviour of untreated woven jute and glass fabric-reinforced epoxy hybrid composites has been investigated experimentally. The orientation of glass and jute fabric was kept at (0°–90°) and (45°–45°) for all stacking sequences. All the laminates were prepared using four plies, and, the number and position of glass layers were varied so as to obtain four different stacking sequences. The erosion rate of these composites were evaluated at different impingement angles (30°–90°) at three different impact velocities (V = 48, 70, 82 m/s). Silica sand was used as the erodent. Our results showed that the impingement angle had a significant influence on the erosion rate. The composite materials showed semi-ductile behaviour with the maximum erosion at an impingement angle of 60°. The morphologies of the eroded surface were observed by a scanning electron microscope, and the possible erosion mechanisms were discussed.     

Experimental and Simulation Studies on the Solid-Particle Erosion of WC-MgO Composites

This article reports our recent studies on WC-4.3 wt% MgO composites with a particular interest in the effect of grain-growth inhibitors (VC and Cr₃C₂) addition on its resistance to erosive wear. It is shown that the maximum erosion rate of the WC-MgO composite occurred at an impingement angle of 90°. With the addition of the grain-growth inhibitors (0.25 wt% VC and 0.25 wt% Cr₃C₂), the erosion resistance increased, particularly profound at the impingement angle of 90°, due to refined microstructures with improved mechanical properties. In addition, computational simulation based on a microscale dynamic model was conducted to investigate the effects of the grain boundary strength and grain size on the erosion resistance of the WC-MgO composites in order to better understand the microstructural effect on the erosive performance of the composites. It is demonstrated that the grain refinement with weak grain boundary strength has a negative effect on the erosion resistance.     

Effects of fibre content and relative fibre-orientation on the solid particle erosion of GF/PP composites

The erosive wear behaviour of glass fibre (GF) reinforced thermoplastic polypropylene (PP) composites was studied in a modified sandblasting apparatus as a function of the impact angle (30, 60 and 90°), relative fibre-orientation (parallel Pa and perpendicular Pe), fibre length (discontinuous, continuous) and fibre content (40–60 wt.%).The results showed a strong dependence of the erosive wear on the relative fibre-orientation at low impact angles (30°), but hardly any difference for 60 and 90° impact angles. In contrast, the fibre length did not affect the erosive wear behaviour especially at high impact angles.The inclusion of brittle GF led to higher erosive wear rates (ER) of the GF/PP composites; the higher the fibre content, the higher was the ER. Nevertheless, the composites still failed in a ductile manner. Different approaches proposed to describe the relationship between ER and fibre content were applied. Best results were generally delivered with the inverse rule of mixture. The modified rule of mixtures proposed for abrasive wear do not seem to apply for erosive wear.     

2Cr13不锈钢表面电火花强化及磨损和冲蚀行为研究

采用电火花表面沉积(ESD)技术,选用YG-8硬质合金和石墨两种电极,对2Cr13不锈钢进行表面强化处理。研究了强化层深度的影响因素,采用辉光放电谱仪(GDS)测试强化层元素分布,用X射线衍射仪(XRD)分析组织结构,用球盘磨损试验机评价耐磨性能,用喷砂型冲蚀装置评价冲蚀性能。结果表明:强化层与基体为冶金结合,其深度随电源电压增加而增大,Ar气保护能有效地降低强化层中N、O含量。石墨电极强化层存在大量的Fe3C、奥氏体和少量石墨;硬质合金电极强化层存在大量的W2C、Co6W6C和WC1-x。经YG-8和C电极强化后,2Cr13不锈钢表面的硬度大幅度提高,摩擦系数明显降低,粘着磨损得到有效的控制,耐磨性能得到显著的改善。在10°小冲蚀角条件下,强化层明显提高了基体的抗石英砂冲蚀性能,而90°垂直冲蚀时,强化层的抗冲蚀性能却不及基体,原因是强化层韧性不及基材。     

Solid particle erosion of CFRP composite with different laminate orientations

The solid particle erosion behavior of epoxy base unidirectional and multidirectional carbon fiber reinforced plastic composites was investigated. The erosion rates of these composites were evaluated at various impingement angles (15–90°) with a particle velocity of 70 m/s. Irregular SiC particles with an average diameter of 80 μm was used. The dependence of impingement angle on the erosive wear resembled the conventional ductile behavior with maximum erosion rate at 15–30° impingement angle. The erosion rate of unidirectional composites at acute impingement angle was higher for [90] than for [45] and [0] while the difference disappeared at normal impingement angle (90°). On the other hand, the erosion rates of multidirectional laminated composites ([0/90], [45/−45], [90/30/−30] and [0/60/−60]) were not much influenced by the fiber orientation except for 15° impingement angle.     

Influence of alumina dispersoid and test parameters on erosive wear behaviour of a cast zinc–aluminium alloy

Observations made pertaining to the erosive wear characteristics of a cast zinc-based alloy and its composite containing 10 wt.% (corresponding to 11.2 vol.%) alumina particles have been presented in this study. Matrix alloy has also been tested under identical test conditions in order to examine the role played by second phase alumina particles on the erosive wear resistance of the matrix alloy. Eroded surfaces and subsurface regions of the specimens were also characterized to understand the operating wear mechanisms.The composite exhibited higher erosive wear resistance (inverse of erosive wear rate) than the unreinforced matrix alloy in general. Further, the wear rate increased with increasing impingement velocity as also evident from higher surface damage. Increasing angle of impingement at lower impinging velocity led to reduced erosive wear rate. On the contrary, the erosive wear rate increased initially with impingement angle, attained the peak and then decreased at still higher angles at the higher impingement velocity. The eroded surfaces showed more abrasion grooves at lower impingement angle and greater tendency of crater formation at higher angles of attack. In case of the composite, protrusion and fracture of the dispersoid phase was also noted. The composite also revealed less severe surface and subsurface damage than the matrix alloy.     

Tribological behavior of metal matrix composites

The wear and friction behavior of continuous graphite fiber reinforced metal matrix composites was investigated. Composite materials were tested against 4620 steel at 54 m s^?1 at room temperature in air without lubricant. The graphite fibers studied included rayon-, pitch- and polyacrilonitrile (PAN)-based fibers. Both high modulus and high strength PAN-based fibers were examined. The fibers were incorporated into copper- and silver-based alloys by means of a liquid metal infiltration technique. The results of this study indicate that the type of graphite fiber in the composite is the most significant factor in the wear and friction behavior of metal matrix composites. In some high modulus fiber tin-bronze composites the fiber fraction influences the wear rate but not the coefficient of friction. Neither the matrix alloy nor the composite tensile strength per se correlate with the friction and wear properties; however, there are specific trends for the various matrix alloys.     

Tribological behavior of graphite-containing nickel-based composite as function of temperature,load and counterface

Nickel-based graphite-containing composites were prepared by powder metallurgy method. Their mechanical properties at room temperature and friction and wear properties from room temperature to 600 °C were investigated by a pin-on-disk tribometer with alumina, silicon nitride and nickel-based alloy as counterfaces. The effects of graphite addition amount, temperature, load, sliding speed and counterface materials on the tribological properties were discussed. The micro-structure and worn surface morphologies were analyzed by scanning electron microscope (SEM) attached with energy dispersive spectroscopy (EDS). The results show that the composites are mainly consisted of nickel-based solid solution, free graphite and carbide formed during hot pressing. The friction and wear properties of composites are all improved by adding 6–12 wt.% graphite while the anti-bending and tensile strength as well as hardness decrease after adding graphite. The friction coefficients from room temperature to 600 °C decrease with the increase of load, sliding speed while the wear rates increase with the increasing temperature, sliding speed. The lower friction coefficients and wear rates are obtained when the composite rubs against nickel-based alloy containing molybdenum disulfide. Friction coefficients of graphite-containing composites from room temperature to 600 °C are about 0.4 while wear rates are in the magnitude of 10^?5 mm³/(N m). At high temperature, the graphite is not effective in lubrication due to the oxidation and the shield of ‘glaze’ layer formed by compacting back-transferred wear particles. EDS analysis of worn surface shows that the oxides of nickel and molybdenum play the main role of lubrication instead of graphite at the temperature above 400 °C.     

Erosive wear properties of unidirectional carbon fiber reinforced PEEK composites

The erosive wear properties of unidirectional carbon fiber (CF) reinforced polyetheretherketone (PEEK) composites were studied. A semi-ductile erosive wear manner was found regardless of the CF orientation. Wear mechanism analysis revealed that both cutting and deformation mechanisms existed in the erosion of the composites, although different damaging forms were involved depending on the impingement angles and CF orientation. To give further support on the erosion mechanisms, a special procedure was designed to observe the cross-sectional surface of the eroded composites, and the surface temperature variation was registered. It increased with increasing impingement angle, indicating higher energy dissipation by deformation, which is consistent with the revealed shift of the main erosive wear mechanism from cutting to deformation and “wholesale” fiber fracture.     

Friction and wear behavior of steam-oxidized ferrous PM compacts

This study determines density effect by assessing sintering temperature and graphite content on the dry sliding wear characteristics of steam-treated iron materials using a pin-on-disk wear test. The specimens were prepared from atomized premixed iron base powders and contained 0.1 to 1.0 wt.% carbon compacted at different densities (5.9 g/cc to 6.8 g/cc). The specimens were sintered for 1 h at different sintering temperatures (1090°C to 1130°C), and then subjected to continuous steam treatment at 540°C for 95 min through in situ Powder metallurgy (PM) technique. Steam treatment was proposed to improve the wear performances of the components of PM. Wear tests were conducted using a pin-on-disk-type machine. Load ranged from 20 N to 60 N. Sliding distance and sliding velocity of 312 m and 0.26 m/s, respectively, were adopted for all tests. Scanning electron microscope was used to analyze wear surface. Increased density and graphite content reduced the wear rate of steam-treated materials. Hardness increased with increasing graphite content. Wear mechanism, wear rate map, and wear maps were drawn for the test result data. Wear transition map identified mild, severe, and ultra-severe wear regimes as functions of applied load.

     

Slurry Erosion Wear Resistance and Impact-Induced Phase Transformation of Titanium Alloys

Erosion wear resistance and impact-induced phase transformation of titanium alloys TA2 (pure Ti), TC4 (Ti–6Al–4V) and TC11 (Ti–6.5Al–3.5Mo–1.5Zr–0.3Si) were investigated using a slurry jet tester. The slurry erosion wear resistance of TA2 is comparable to that of 304 stainless steel, especially at the impingement angle 90°. Although TC4 and TC11 have higher hardness, TA2 possesses the best erosion wear resistance except TC11 at 15°. With the increasing erosion time, the eroded surface hardness of TC11 at the impingement angle 90° increases and then decreases, while the volume loss rate drops in the first 15 min, then increases until 30 min, and then slightly decreases again. With XRD characterization and SEM observation, erosion-induced phase transformation from metastable β-phase to α-phase is proved on the surface of titanium alloy TC11. And the thickness of visible phase transformation layer is about 10 μm. Phase transformation influences the erosive wear mechanism of titanium alloys. At the impingement angle of 30°, the material removal of TC4 and TC11 can be described as micro-plowing and lip extruding, while plowing mark is not a typical surface morphology of TA2, indicating a better work-harden ability. So, stabilizing β-phase can be an effective way to improve the erosion wear resistance of titanium alloys.     

The Mechanical Mixed Layer and Its Role in Cu-15Ni-8Sn/Graphite Composites

This article provides an in-depth investigation into the formation of the mechanical mixed layer (MML) and its role in Cu-15Ni-8Sn/graphite composites. Wear tests were conducted at room temperature using a ring–block configuration with an applied load of 50 N and sliding speed of 0.42 m/s. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) were performed to analyze the worn surfaces and subsurfaces. Results indicated that high graphite content contributed to the formation of a protective MML. When the MML formed on the tribosurface as the graphite content increased, both the friction coefficient and wear rate greatly decreased. The friction coefficient with a stable value of 0.075 and wear rate of 6.10 × 10^?16 (m³/N· m) were the lowest when an apparent tribolayer appeared at the graphite content of 38 vol%. The characteristics of the MML and its influence on wear mechanisms of the composites are discussed. The MML existing on the worn surface protected the materials from severe adhesion and abrasion and the predominant wear mechanisms changed to delamination, which resulted in the drastic changes in wear resistance and friction coefficient.     

Solid particle erosion of unidirectional carbon fibre reinforced polyetheretherketone composites

The solid particle erosion behaviour of unidirectional carbon fibre (CF) reinforced polyetheretherketone (PEEK) composites has been characterised. The erosion rates of these composites have been evaluated at different impingement angles (15–90°) and at three different fibre orientations (0, 45, and 90°). The particles used for the erosion measurements were steel balls with diameter of 300–500 μm and impact velocities of 45 and 85 m/s. The unidirectional CF reinforced PEEK composites showed semi-ductile erosion behaviour, with maximum erosion rate at 60° impingement angle. The fibre orientations had a significant influence on erosion rate. The morphology of eroded surfaces was examined by using scanning electron microscopy (SEM). Possible erosion mechanisms are discussed.     

Friction and Wear Behavior of Copper Matrix Composites Reinforced with SiC and Graphite Particles

The objective of this paper is to investigate the friction behavior and wear mechanism of copper matrix composites reinforced with SiC and graphite particles. The results indicate that a graphite-rich mechanically mixed layer (MML) formed on the tribo-surface was responsible for the good tribological properties of the hybrid composites at low normal loads. When graphite content was high enough for delamination wear to take place at high load, wear resistance deteriorated. A continuous supply of graphite to the tribo-surface is an important precondition for the formation of a graphite-rich MML and the benefit of its anti-friction properties for the copper hybrid composites.     

Tribological Properties of Graphite-Fiber-Reinforced,Partially Fluorinated Polyimide Composites

Graphite-fiber-reinforced polyimide (GFRPI) composites were formulated form three new partially fluorinated polyimides and three types of graphite fiber. Nine composites were molded into pins and evaluated in a pin-on-disk tribometer. Friction coefficients, wear rates, pin wear surface morphology, and transfer film formation were assessed at 25 and 300°C. Also assessed was the effect of sliding distance on friction and the effect of constantly increasing or decreasing temperature on friction. Wear was up to two orders of magnitude lower at 25°C and up to one order of magnitude lower at 300°C than with previously formulated NASA GFRPI composites.     

Erosive Wear Mechanism of New SiC/SiC Composites by Solid Particles

A solid-particle erosive wear test by impinging silicon carbide (SiC) powders was carried out at room temperature over a range of median particle sizes of 425–600 μm, speed of 100 m/s and impact angle of 90° and assessed by wear measurements and scanning electron microscopy. Erosive wear behaviour was examined on newly fabricated nano-powder infiltration and transient eutectoid (NITE) SiC/SiC composites and two commercial composites by the chemical vapour infiltration (CVI) and NITE fabrication route. Microstructural observation was performed to examine the correlation between erosive wear behaviours and fabrication impurities. Conspicuous defects were observed in the prototype materials as the forms of porosity, fibre deformation, residual oxide, pyrolytic carbon (PyC) deformation, PyC cleavage, among others. Erosive wear behaviour was rather serious in the prototype of fabricated composites, which employ pre-SiC fibre and phenolic resin. Two dominant erosive wear mechanisms were observed: delamination of constituents, mainly caused by erosive crack propagation, and fragmentation and detachment of constituents, which usually resulted from erosive impact. A unit size of delamination was the most decisive factor affecting wear volume. The bonding strength of each constituent was mostly affected by various forms of porosities. Therefore, the fundamental cause and subsequent results must be carefully elucidated. The correlation of microstructural defect and wear behaviour was investigated with the aim of reducing dominant wear by improving fabrication conditions. The final product of the cost-effective composite had a 2.5-fold higher resistance than the commercial CVI composite. Consequently, by controlling fabrication impurities, we have been successful in developing and improving a new fabrication technique; consequently, the known defects are rarely observed in final product. A schematic wear model of erosive wear mechanisms is proposed for the newly fabricated SiC/SiC composites under particle erosion.     

Tribological Properties of PTFE and PTFE Composites at Different Temperatures

The friction and wear properties of polytetrafluoroethylene (PTFE) and its composites with fillers such as bronze, glass fiber, carbon fiber, carbon, graphite, and polymer were studied at ambient temperature and high temperature. The wear resistance and hardness were enhanced by the fillers. Results showed that the wear resistance of all composites was much higher than that of pure PTFE. Pure PTFE has the lowest friction coefficient at ambient temperature (temperature: 23 ± 2°C, humidity: 50 ± 10%) but highest friction coefficient at high temperature (above 100°C). The PTFE composite filled with bronze showed the best wear resistance at ambient temperature but the poorest wear resistance at high temperature. The carbon-graphite- or polymer-filled PTFE composite showed a lower friction coefficient and moderate wear resistance at both ambient and high temperature.