Dry sliding wear characteristics of in situ synthesized Al-TiC composites

Abstract

Aluminum-based composites containing 0.06, 0.09, 0.12 fractions of in situ-synthesized TiC (Titanium carbide) particles have been prepared through in-melt reaction from Ai–SiC–Ti system following a simple and cost-effective stir-casting route. The TiC forms by the reaction of Ti with carbon which is released by SiC at temperatures greater than 1073 K. However, some amount of titanium aluminide (Al₃Ti) is also formed. The formation of TiC has been confirmed through X-ray diffraction studies of the composite. The hardness and tensile strength have been found to increase with increasing amount of TiC. The friction and wear characteristics of the composites have been determined by carrying out dry sliding tests on pin-on-disc machine at different loads of 9.8 N, 19.6 N, 29.4 N, 39.2 N at a constant sliding speed of the 1 m/s speed. The wear rate i.e. volume loss per unit sliding distance has been found to increase linearly with increasing load following Archard’s law. However, both the wear rate and friction coefficient have been observed to decrease with increasing amount of TiC in the composite. This has been attributed to (i) a relatively higher hardness of composites containing relatively higher amount of TiC resulting in a relatively lower real area of contact and (ii) the formation of a well-compacted mechanically mixed layer of compacted wear debris on the worn surface which might have inhibited metal–metal contact and resulted in a lower wear rate as well as friction coefficient.     

Tribological behavior of Al-based self-lubricating composites

Abstract

Aluminum-based composites containing either SiC (Al10%SiC) as the hard phase or a combination of SiC and MoS₂ (Al10%SiC4%MoS₂) have been synthesized following stir casting route. To overcome the poor wetting characteristics, magnesium was added in one of the composites (Al10%SiC4%MoS₂4%Mg) to improve the bonding between matrix and second phase. The results suggested an enhancement in hardness and strength of the composite containing SiC–MoS₂ and Mg, thus indicating the effectiveness of Mg addition in improving the interfacial bonding strength. Tribological performance of the composites has been examined by carrying out pin-on-disk wear tests under dry sliding conditions at different normal loads of 9.8, 14.7, 19.6, and 24.5 N and at a constant sliding speed of 1 m/s. Both the friction coefficient and the wear rate have been found to reduce with addition of MoS₂; however, bonding between the matrix and reinforcements was not good. Al10%SiC4%MoS₂4%Mg has shown the best tribological performance at all the loads in terms of the lowest friction coefficient and the lowest wear rate. The wear mechanism has been found to be a combination of adhesion and abrasion as indicated by the presence of some abrasive grooves and delaminated flakes at the worn surface and the X-ray examination of wear debris for all the materials used in the present investigation.     

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.     

Structural and Tribological Properties of Polytetrafluoroethylene Composites Filled with Glass Fiber and Al2O3 in Atomic Oxygen Environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of polytetrafluoroethylene (PTFE) composites filled with both glass fibers and Al₂O₃ were investigated in a ground-based simulation facility, in which the average energy of AO was about 5 eV and the flux was 5.0 × 10¹⁵/cm² s. It was found that AO irradiation first induced the degradation of PTFE molecular chains on the sample surface, and then resulted in a change of surface morphology. The addition of Al₂O₃ filler significantly increased the AO resistance property of PTFE composites. Friction and wear tests indicated that AO irradiation affected the wear rate and increased the friction coefficient of specimens. The PTFE composite containing 10% Al₂O₃ exhibit the best AO resistance and lower wear rate after long time AO irradiation.     

Effect of temperature on the sliding wear behavior of laser surface alloyed Ni-base on Al-Mg-Si alloy

The surface microstructures of 6061 Al-Mg-Si alloy coated with laser surface alloyed (LSA) Ni-Cr-B-Si powder and their sliding wear performance have been investigated. Experimental results show that there are three regions, as grayish region (G.R.), dark region (D.R.) and bright region (B.R.), in the pool. The Al₃Ni and Al₃Ni₂ compounds appear in the G.R. and D.R., respectively. The Al-Ni-Cr amorphous structure can be observed in the B.R. The hardness of the LSA specimens is much higher than the Al-matrix. Compared with the Al-matrix, the LSA specimens have excellent sliding wear performance. They have lower friction coefficient and wear rate. The critical temperature of sliding wear resistance of LSA specimen is higher than that of Al-matrix by about 50 °C. The stress relief during thermal treatment will slightly reduce the hardness and the wear resistance of LSA specimens, especially at testing temperature >200 °C.     

Wear resistance of CuZr-based amorphous-forming alloys against bearing steel in 3.5% NaCl solution

Abstract

To investigate the amorphous-crystalline microstructure on the tribocorrosion of bulk metallic glasses (BMGs), 6 mm diameter rods of Cu_46-xZr₄₇Al₇Ag_x (x = 0, 2, 4) amorphous-forming alloys with in situ crystalline and amorphous phases were fabricated by arc-melting and Cu-mould casting. Using a pin-on-disc tribometer, the tribo-pair composed by CuZr-based amorphous-forming alloys and AISI 52100 steel were studied in 3.5% NaCl solution. With the increase of Ag content from 0 to 4 at.%, the compressive fracture strength and the average hardness decrease firstly and then increase. Moreover, 4 at.% Ag addition increases the amount of amorphous phase obviously and inhibits the formation of brittle crystalline phase, resulting in the improvement of corrosion resistance and the corrosive wear resistance. The primary wear mechanism of the BMG composites is abrasive wear accompanying with corrosive wear. The tribocorrosion mass loss of Cu₄₂Zr₄₇Al₇Ag₄ composite is 1.5 mg after 816.8 m sliding distance at 0.75 m s^?1 sliding velocity under 10 N load in NaCl solution. And the volume loss evaluated from the mass loss is about 20 times lower than that of AISI 304 SS. Thus, Cu₄₂Zr₄₇Al₇Ag₄ composite may be a good candidate in the tribology application under marine environment.     

Structural and Tribological Properties of Polyimide/Al2O3/SiO2 Composites in Atomic Oxygen Environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of polyimide/Al₂O₃/SiO₂ composites were investigated in a ground-based simulation facility, in which the energy of AO was about 5 eV and the flux was 7.2 × 10¹⁵ cm^?2.s^?1. The structural changes were characterized by X-ray photoelectron spectroscopy (XPS) and attenuated total-reflection FTIR (FTIR-ATR), while the tribological changes were evaluated by friction and wear tests as well as scanning electron microscopy (SEM) analysis of the worn surfaces. It was found that AO irradiation induced the oxidation and degradation of polyimide (PI) molecular chains. The destructive action of AO changed the surface chemical structure, which resulted in changes of the surface morphology and chemical composition of the samples. Friction and wear tests indicated that AO irradiation decreased the friction coefficient but increased the wear rate of both pure and Al₂O₃/SiO₂ filled PIs.     

Factors affecting the microstructure and mechanical properties of Ti-Al3Ti core-shell-structured particle-reinforced Al matrix composites

This work studied the effects of matrix powder and sintering temperature on the microstructure and mechanical properties of in situ formed Ti–Al₃Ti core–shell-structured particle-reinforced pure Al-based composites. It has been shown that both factors have significant effects on the morphology of the reinforcements and densification behaviour of the composites. Due to the strong interfacial bonding and the limitation of the crack propagation in the intermetallic shell during deformation by soft Al matrix and Ti core, the composite fabricated using fine spherical-shaped Al powder and sintered at 570 °C for 5 h has the optimal combination of the overall mechanical properties. The study provides a direction for the optimum combination of high strength and ductility of the composites by adjusting the fabrication parameters.     

The tribology properties of alumina/silica composite nanoparticles as lubricant additives

The as-prepared alumina/silica (Al₂O₃/SiO₂) composite nanoparticles were synthesized with a hydrothermal method and modified by silane coupling agent. The tribological properties of the modified Al₂O₃/SiO₂ composite nanoparticles as lubricating oil additives were investigated by four-ball and thrust-ring tests in terms of wear scar diameter, friction coefficient, and the morphology of thrust-ring. It is found that their anti-wear and anti-friction performances are better than those of pure Al₂O₃ or SiO₂ nanoparticles. When the optimized concentration of nanoparticle additive is 0.5 wt.%, the diameters of wear scar and friction coefficients are both smallest. Such modified composite nanoparticles can adsorb onto the friction surfaces, which results in rolling friction. Therefore, the friction coefficient is reduced.     

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.     

Synthesis of anodizing composite films containing superfine Al2O3 and PTFE particles on Al alloys

Anodized composite films containing superfine Al₂O₃ and PTFE particles were prepared on 2024 Al alloy using an anodizing method. The microstructures and properties of the films were studied by scanning electron microscopy, optical microscopy and X-ray diffraction. Friction wear tests were performed to evaluate the mechanical properties of the composites. Results indicate that the composite films with reinforced Al₂O₃ and PTFE two-particles have reduced friction coefficients and relatively high microhardness. The friction coefficient can be as small as 0.15, which is much smaller than that of an oxide film prepared under the same conditions but without adding any particles (0.25), while the microhardness can reach as high as 404 HV. When rubbed at room temperature for 20 min during dry sliding friction tests, the wear loss of the film was about 16 mg, which is about the half of that of the samples without added particles. The synthesized composite films that have good anti-wear and self-lubricating properties are desirable for oil-free industrial machinery applications.     

Dry sliding wear behavior of Al-SiO2 composites

Abstract

Al-base composites with different amount of silica (5, 10, 15 and 20 wt.%) were developed using powder metallurgy route and compacts were sintered at 550 °C for 2 h. XRD analysis of all compositions was conducted for phases and amount of the second phase present. Morphology of the composites shows quite uniform distribution of the SiO₂ particles but at higher percentage of SiO₂ particles the clustering starts. Mechanical properties such as uniaxial compressive strength (UCS) and hardness were evaluated and it is seen that among all compositions, composite with 10 wt.% SiO₂ has maximum UCS and hardness. Wear behavior of all composites was studied with sliding distance, applied loads, sliding velocity and composition. All composites show a linear increase in cumulative wear with distance and load. Wear rate with load increases continuously for all compositions, however, composite with 10 wt.% SiO₂ revealed minimum wear rate with distance, sliding velocity and loads. Wear rate with sliding velocity increases sharply after attaining minima at 3 m/s sliding velocity. SEM analysis of wear tracks is in agreement with wear results. Al-10 wt.%SiO₂ also shows minimum wear coefficient values for all loads, however, wear coefficient decreases with load for all compositions.     

Nanoparticle dispersion effect of laser-surface melting in ZrB<Subscript>2p</Subscript>/6061Al composites

Zirconium diboride (ZrB_2p, 15 vol%)/6061 aluminum (Al) composites were fabricated via in situ reaction. The existence, morphologies, and dispersion degree of the in situ ZrB₂ particles with size from tens to hundreds of nanometers were studied by X-ray diffractometry, energy-dispersive X-ray spectroscopy, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy. As the particle-settlement effect becomes dominant during the composite fabrication process, ZrB₂ nanoparticles agglomerate to a certain extent in some areas of the as-cast composites. A laser-surface melting (LSM) strategy was applied to disperse agglomerated ZrB₂ nanoparticles in as-cast composites, and the ZrB₂ nanoparticle dispersion is affected visibly by LSM. After LSM, nanoparticles tend to distribute along the grain boundary. Particle clusters were dispersed in an explosive orientation and the particle diffusion distance varied in terms of its radius and melt-viscosity vicinity. High-resolution transmission electron microscopy showed the existence of a subgrain structure near the ZrB₂–Al interface after LSM. This may increase the yield strength when a dislocation tangle forms.     

Tribological Properties of Thermosetting Polyimide/TiO2 Nanocomposites Under Dry Sliding and Water-Lubricated Conditions

Thermosetting polyimide(PI)-based nanocomposites containing various contents of nano-TiO₂ were fabricated via an in situ polymerization of monomer reactants (PMR) process. Under dry sliding and water-lubricated conditions the friction and wear behaviors of the PMR PI and its nanocomposites were evaluated and compared. The addition of nano-TiO₂ in PI contributed to improving the friction and wear behavior considerably under dry sliding. The highest change ratio of wear rate was 61% with the optimum nano-TiO₂ content of 3%, while the highest change of friction coefficient was 60% with the optimum nano-TiO₂ content of 9%. Under water-lubricated condition, contrarily, the addition of nano-TiO₂ in PI does harm to the tribological properties. Namely, the friction coefficient of the nanocomposites increased with increasing the nano-TiO₂ content. These results may be caused by the following facts: the hardness of the PI matrix would be increased by adding the nano-TiO₂ reducing the ability of elastic deformation of the nanocomposites; accordingly, the poor elastic deformation hindered the formation of a water-lubrication film on the surface. An investigation on the wear tracks indicated that the wear mechanism of PI/TiO₂ nanocomposites under dry sliding condition proceeded from fatigue wear to a combination of fatigue wear and abrasive wear with increasing the mass fraction of nano-TiO₂.     

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.     

Friction and Wear Behaviors of the Polydimethylsiloxane Bishydroxyalkyl-Terminated Modified Polyurethane Composites Filled with the Barium Sulfate in Dry Friction and Water Lubrication

The addition of less than 20 wt% of approximate 1 micron barium sulfate (BaSO₄) into polyurethane (PU) composites modified by bishydroxyalkyl-terminated polydimethylsiloxane (PDMSBH) resulted in increases in mechanical strength and thermal conductivity and, at the same time, resulted in improvements in the friction and wear properties of the polyurethane composites. These polyurethane composites were suitable for marine use for bearings at high load under dry friction and at fast sliding speed under water lubrication. Characterization with Fourier transform infrared (FTIR) spectroscopy, thermogravimetry analysis (TGA), scanning electron microscope (SEM), and an MRH-3 ring-on-block wear tester indicated that the addition of BaSO₄ disrupts the organic phase separation in the polyurethane, resulting in better tribological properties, but there is no special chemical reaction between the particles and polyurethane. Adding too much BaSO₄ resulted in higher wear rate because of inorganic–organic phase separation.     

Effects of Ca/Al ratio and extrusion process on Mg–Al–Ca alloys to produce a high toughness in-situ composite

The microstructures and tensile properties of Mg–Al₂Ca–Mg₂Ca in situ composites (Mg–17Al–8Ca, Mg–14Al–11Ca and Mg–12.5Al–12.5Ca) with different Ca/Al ratios have been studied in both as-cast and extruded conditions. The results indicated that by increasing Ca/Al ratio, new Mg₂Ca intermetallic introduces to the Al₂Ca phase in eutectic structure. Computer-aided cooling curve analysis confirmed the formation of these phases during solidification. Extrusion process not only altered the size of large bulk Al₂Ca intermetallic, but also changed the size and morphology of intermetallics in eutectic structure considerably. The results showed that with increasing Ca/Al ratio, tensile properties of cast composites changes slightly, but significant enhancement is observed after extrusion process. The strength and elongation values of Mg–12.5Al–12.5Ca (Ca/Al = 1) alloy improved from 166 MPa and 2% in as-cast condition to 465 MPa and 12% in hot-extruded condition. The reason for the improved toughness may be attributed to the formation of finer and well-dispersed distribution of hard (Al₂Ca) and ductile (Mg₂Ca) phases. It was found that hot extrusion easily deforms ductile Mg₂Ca phase in comparison with Al₂Ca phase. In as-extruded condition, there are more very fine dimples than as-casted condition because extrusion process leads to formation of fragmented tiny particles and more uniformity distribution of Al₂Ca particles.     

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.     

The Effects of Copper and Polytetrafluoroethylene (PTFE) on Thermal Conductivity and Tribological Behavior of Polyoxymethylene (POM) Composites

The effects of copper and polytetrafluoroethylene (PTFE) on thermal conductivity and tribological behavior of polyoxymethylene (POM) composites were investigated by a hot disk thermal analyzer and an M-2000 friction and abrasion testing machine. The results indicated that the incorporation of 3 wt% copper particles into POM had little effect on the thermal conductivity of POM composites, but led to the decreased friction coefficient and wear rate of composites. As the copper content was increased, the thermal conductivity increased and reached 0.477 W m^?1 K^?1 for POM-25% Cu composite, an increase of 35.9% compared with that of unfilled POM, while the friction coefficient and wear rate of composites also increased. The incorporation of PTFE into POM-Cu composites had a negligible effect on the thermal conductivity of composites, but helped in the formation of a continuous and uniform transfer film and resulted in the reduction in the friction coefficient and wear rate of composites. The POM-15% Cu-10% PTFE composite, with a value of wear rate similar to unfilled POM possessed higher thermal conductivity and lower friction coefficient.     

Electrodeposition and tribological properties of Ni-SrSO4 composite coatings

Ni-SrSO₄ composite coatings were electrodeposited on superalloy Inconel 718 from a Watts electrolyte containing a SrSO₄ suspension. Ni-SrSO₄ coatings were investigated by scanning electron microscope, microhardness tester, and friction and wear tester in sliding against a bearing steel ball under unlubricated condition. The incorporation of SrSO₄ into Ni matrix increases the microhardness of electrodeposited coatings. Ni-SrSO₄ composite coating exhibits a distinctly low friction coefficient and a small wear rate as contrasted with pure Ni coating and the substrate. The effect of SrSO₄ particles on microstructure and tribological properties of Ni-SrSO₄ composite coatings is discussed.