Mechanical Properties and Tribological Behavior of Al6061–SiC–Gr Self-Lubricating Hybrid Nanocomposites

In the present investigation, a newly fabricated Al6061 reinforced with various quantity (0.4–1.6 wt%) of nano SiC in steps of 0.4 and fixed quantity (0.5 wt%) of micro graphite particle’s hybrid nanocomposites were prepared by ultrasonic assisted stir casting method. The influence of nano SiC and graphite content on the mechanical and tribological properties of Al6061 hybrid nanocomposites were studied. The pin-on-disc equipment was used to carry out experiment at 10–40 N applied load, 0.5 m/s sliding speed and 1000 m sliding distance. The Al/SiC/Gr hybrid nano-composite and matrix alloy wear surfaces were characterized by FESEM equipped with an EDS, 3D profilometer to understand the wear mechanisms. The results of Al/SiC/Gr self-lubricating hybrid nano-composites showed improved wear resistance than the Al6061 matrix alloy. The co-efficient of friction of Al/SiC/Gr hybrid nano-composites were lower than those of the unreinforced alloy at various applied load. Compared to matrix alloy, the surface roughness of Al/SiC/Gr hybrid nano-composites had significantly reduced to 66% at low load and 75% at high load. Self-lubricating Al/SiC/Gr hybrid nanocomposites showed superior surface smoothness compared to matrix alloy.     

Response Surface Methodology Based Modelling of Friction–Wear Behaviour of Al6061/9%Gr/WC MMCs and Its Optimization Using Fuzzy GRA

In the present paper an attempt is made to establish a response surface methodology based non-linear mathematical model for the friction–wear behaviour of as cast and heat-treated Al6061/9%Gr/WC (with WC at 1, 2 and 3 wt%) metal matrix composites (MMCs). During experimentation, the process parameters, namely percentage of WC, load, sliding distance and sliding velocity have been considered as inputs and wear loss (WL) and coefficient of friction (COF) have been treated as the responses. Results reveal that, for as-cast Al6061/9%Gr/WC hybrid composites, the WL decreases with increase in percentage of WC and increases with the increase in load, sliding distance and sliding velocity. Moreover, COF decreases with increase in percentage of WC and sliding velocity and increases with increase in the load and sliding distance. It has also been observed that the WL and COF of heat treated composites are found to be less than the as cast MMCs. Further, fuzzy grey relational analysis (GRA) has been used to perform the multi objective optimization of the said wear process. Finally, the evidence of wear phenomenon for the said composites have been examined with the help of scanning electron microscopy.     

Statistical Analysis of Tribological Properties of Aluminum Matrix Composites Using Full Factorial Design

This work describes the tribological properties of mono AA6061-10 wt% B₄C and hybrid AA6061-10 wt% B₄C-7.5 wt% Gr composites which could be used as a potential substitute for aluminum alloys used in automotive engines. The tribological experiments are performed as per the experimental scheme designed using full factorial design. The results suggest that the wear loss increases with applied load and sliding distance and the friction coefficient increases with increase in applied load. Further, the ANOVA analysis reveals the statistically and physically significant factors which influence the wear loss and friction coefficient. Formation of Gr-rich tribolayer causes reduction in the wear loss and friction coefficient for hybrid composites compared to the mono ones.     

Wear Behavior of Aluminum Matrix Hybrid Composites Fabricated through Friction Stir Welding Process

Effects of friction stir processing (FSP)parameters and reinforcements on the wear behavior of 6061-T6 based hybrid composites were investigated.A mathematical formulation was derived to calculate the wear volume loss of the composites.The experimental results were contrasted with the results of the proposed model.The influ-ences of sliding distance,tool traverse and rotational speeds,as well as graphite (Gr)and titanium carbide (TiC) volume fractions on the wear volume loss of the composites were also investigated using the prepared formulation. The results demonstrated that the wear volume loss of the composites significantly increased with increasing sliding distance,tool traverse speed,and rotational speed;while the wear volume loss decreased with increasing volume fraction of the reinforcements.A minimum wear volume loss for the hybrid composites with complex reinforcements was specified at the inclusion ratio of 50% TiC+50% Al2 O3 because of improved lubricant ability,as well as resist-ance to brittleness and wear.New possibilities to develop wear-resistant aluminum-based composites for different in-dustrial applications were proposed.     

Determination on the Effect of Ti Addition on the Microstructural,Mechanical and Wear Behavior of Cu–6Sn Alloy in as—Cast Condition

The objective of this research is to fabricate a ternary alloy (Cu–Sn–Ti), incorporating titanium into bronze with varying weight percentage of titanium (0.5 wt%, 1 wt%) to investigate its impact on microstructural and mechanical properties and wear behavior and to collate these results with those of conventional bronze (Cu–6Sn). The microstructure of the alloys was observed using a metallurgical microscope, and results exhibit a finer grain refinement in the dendritic structure, which causes an improvement in mechanical properties. The mechanical properties were tested (tensile strength, hardness), and they showed an increment in values corresponding to the increase in the weight percentage of titanium. However, owing to the formation of an inclusion (blowhole), there was a reduction in the tensile strength for Cu–6Sn.0.5Ti. The wear analysis was also carried out using a pin-on-disk tribometer with selected parameters of load (10–30 N), sliding distance (1000 m) and sliding velocity (1–3 m/s), and it was noted that there was an increase in the wear rate with an increase in load and distance for all combinations of parameters. There was also an improvement in the wear resistance with an increase in the weight percentage of Ti, in comparison with the conventional base alloy.     

Wear Behavior of a Novel Aluminum-Based Hybrid Composite

In the current research, the dry sliding wear behaviors of 6351 Al alloy and its composite with hybrid reinforcement (ex situ SiC and in situ Al₄SiC₄) were investigated at low sliding speed (1 m s^?1) against a hardened EN 31 disk at different loads. The wear mechanism involved adhesion and microcutting-abrasion at lower load. On the other hand, at higher load, abrasive wear involving microcutting and microplowing along with adherent oxide formation was observed. Initially, under higher load, the abrasive wear mechanism caused rapid wear loss up to a certain sliding distance. Afterward, by virtue of frictional heat generation and associated temperature rise, an adherent oxide layer was developed at the pin surface which drastically reduced the wear loss. The overall wear rate increased with load in alloy as well as in composite. Moreover, the overall wear rate of the composite was found lower than that of the 6351 Al alloy at all applied loads. The ex situ SiC particles were found to resist abrasive wear, while, in situ Al₄SiC₄ particles offered resistance to adhesive wear. Accordingly, the 6351 Al (SiC + Al₄SiC₄) hybrid composite exhibited superior wear resistance relative to the 6351 Al alloy.     

Development of Wear Mechanism Map for Al–4Mg Alloy/MgAl 2 O 4 In Situ Composites

Dry sliding wear behaviour of Al–4Mg alloy and Al–4Mg alloy/MgAl2O4 in situ composites was examined under normal loads of 10–30 N at sliding speeds of 1, 3, 5 and 7 m/s and sliding distance of 1500 m using a pin-on-disc apparatus. Al–4Mg alloy with different wt% (1, 2 and 3) of MgAl2O4 in situ composites was synthesized via ultrasonic cavitation by the addition of H3BO3 powders. Unreinforced alloy and composites were characterized to conclude the role of MgAl2O4 in modifying the wear behaviour of the composite. Worn-out samples and wear debris were examined by scanning electron microscopy and X-ray diffraction in order to obtain the major wear mechanisms of the developed composites. The addition of MgAl2O4 significantly reduces the wear rate of Al–4Mg alloy at higher loads. The operating wear mechanisms observed were delamination, oxidation, abrasion, adhesive, thermal softening and plastic deformation modes.     

Corrosive wear of SiC Whisker-and particulate-reinforced 6061 aluminum alloy composites

Wear tests on SiC whisker- and SiC particulate-reinforced 6061-T6 aluminum matrix composites (SiCw/Al and SiCp/Al), fabricated using a high pressure infiltration method, were performed in laboratory air, ion-exchanged water and a 3 pct NaCl aqueous solution using a block-on-ring type apparatus. The effects of environment, applied load, and rotational (sliding) speed on the wear prop-erties against a sintered alumina block were evaluated. Electrochemical measurements in ion-ex-changed water and a 3 pct NaCl aqueous solution were also made under the same conditions as the wear tests. A comparison was made with the properties of the matrix aluminum alloy 6061-T6. The SiC-reinforced composites exhibited better wear resistance compared with the monolithic 6061 Al alloy even in a 3 pct NaCl aqueous solution. Increase in the wear resistance depended on the shape, size, and volume fraction of the SiC reinforcement. Good correlation was obtained between corrosion resistance and corrosion wear. The ratios of wear volume due to the corrosive effect to noncorrosive wear were 23 to 83 pct, depending on the wear conditions.     

Physical,mechanical and dry sliding wear properties of hybrid and non-hybrid Al–V nanocomposites produced by powder metallurgy

The present work aims to characterise the sliding wear behaviour of non-hybrid Al–Al₃V and hybrid Al–(Al₃V, Al₂O₃) nanocomposites. Wear rates were calculated from mass loss measurements. X-Ray diffraction (XRD) pattern was utilised to evaluate the microstructural changes during milling hot-pressed samples. It was found that the wear resistance of hybrid nanocomposites was enhanced by increasing Al₃V–Al₂O₃ percentage due to an increase in hardness. The mass loss measurement showed that not only was the wear rate of hybrid samples lower than that of Al–Al₃V, but also it had lower friction coefficients in comparison to the non-hybrid sample. The worn surface evaluation in hybrid samples indicated that the formed darker layer possesses the features of the mechanically mixed layer (MML), which inhibits mass loss intensification. Moreover, formation of MML as a lubricant layer promotes the friction characteristic of the hybrid nanocomposite.     

Influence of Experimental Parameters on Friction and Wear Mechanisms of PA66/PTFE Blend Reinforced with Glass Fiber

Polymer blend of composition 80 wt% polyamide 66/20 wt% polytetraflurotheylene (PA66/PTFE) was selected as a matrix and reinforced with different weight percentage of short glass fibers (SGF). These composites were prepared by melt mix method using twin screw extruder followed by injection molding. The tribological behaviors were tested by using pin on disc machine by varying the different experimental parameters. The friction and wear mechanisms were studied as a function of sliding velocity, sliding load, and distance. The effect of fiber loading lowered the wear volume loss of SGF filled PA66/PTFE blend. The least frictional coefficient of 0.24 was obtained for 20 wt% of SGF in the blend. However, the wear resistance was not apparently improved by SGF loading in the experimental range for comparison with unfilled PA66/PTFE blend. The worn surfaces of specimen were examined by scanning electron microscopy photographs. The observations revealed that the frictional behavior was a function of development and formation of transfer film. Matrix wear and fiber wear were the result of frictional mechanism. The critical wear volume of PA66/PTFE/SGF composites was the contribution of both matrix and fiber wear. The abrasive nature of SGF was also one of the important factor for frictional behavior.     

AS41耐热镁合金的摩擦学行为研究

本文研究了AS41耐热镁合金在室温和200℃时的显微组织、力学和摩擦学性能,并探讨了其在高温的摩擦学机理。研究表明:AS41耐热镁合金主要由基体(α-Mg)相和第二相(Mg17Al12、Mg2Si和MgO相)组成,其在200℃时除延伸率有所增加外,抗拉强度和屈服强度均较室温时显著下降。耐热镁合金的摩擦系数随载荷增大而减小,滑行速度和滑行距离对摩擦系数的影响不大;磨损率随着载荷和滑行距离的增加而增大,但随滑行速度的增加而减小;且耐热镁合金在200℃的摩擦学性能优于其室温摩擦学性能。随着载荷变化,磨损机理发生变化;低载荷时表现为氧化磨损和磨粒磨损;中等载荷时表现为磨粒磨损和轻微剥层磨损;较高载荷时表现为剥层磨损。     

Investigation of Production and Abrasive Wear Behavior of Functionally Graded TiB 2 /Al and TiB 2 /Al–4Cu Composites

In this study, it is aimed to investigate the production and abrasive wear properties of functionally graded TiB2/Al and TiB2/Al–4Cu composites. Using in situ technique, titanium di-boride (TiB2) particles are being spontaneously formed in liquid matrix, resulting in a “Al(l) + TiB2(S)” semisolid at 900 °C. The semisolid solidifies under a centrifugal force at 1500 rpm rotation speed in a steel mold to produce functionally graded composites. The properties of composites such as density, abrasive wear, hardness and microstructure were examined by dividing into four zones from the outside to the inside of the composite. Volume loss of composites were examined by using L16(4124) orthogonal design, considering some factors such as matrix type of composites, region of composites, abrasive particle size, sliding speed and sliding load according to Taguchi method. The results showed that both TiB2/Al and TiB2/Al–Cu composites had two regions: the TiB2-reinforced and non-reinforced regions. It was determined that the volume loss increased with increasing load, speed and abrasive particle size and decreased with increasing TiB2 particles reinforcement ratio.     

Investigation of Mechanical Properties and Dry Sliding Wear Behaviour of Squeeze Cast LM6 Aluminium Alloy Reinforced with Copper Coated Short Steel Fibers

LM6 aluminium alloy with 2.5–10 wt% of copper coated short steel fiber reinforced composites were prepared using squeeze casting process. Microstructure and mechanical properties viz., hardness, tensile strength and ductility were investigated. Dry sliding wear behaviour was tested by considering sliding distance and load. Fracture surface and worn surface were examined using field emission scanning electron microscope (FESEM). Hardness of composites increased with increasing wt% of fiber. Tensile strength of composites increased up to 19% for 5 wt% fiber composites. Further addition of fibers decreased the tensile strength of composites. Ductility of the composites decreased with the addition of fibers into the matrix. Wt% of fibers significantly decreased the weight loss, coefficient of friction and wear rate. Also the cumulative weight loss decreased up to 57% for 10 wt% of composites compared to LM6 aluminium alloy. Fracture surface of composite tensile specimen showed dimple formation and fiber pullout. Worn surface of matrix showed long continuous grooves due to local delamination on the surface. However, worn surface of composites showed fine and smooth grooves due to ploughing rather than local delamination. Copper coated steel fiber reinforcement in LM6 aluminium alloy exhibited better mechanical properties and wear resistance compared to matrix.     

Microstructure–Wear Resistance Correlation and Wear Mechanisms of Spark Plasma Sintered Cu-Pb Nanocomposites

The dispersion of a softer phase in a metallic matrix reduces the coefficient of friction (COF), often at the expense of an increased wear rate at the tribological contact. To address this issue, unlubricated fretting wear tests were performed on spark plasma sintered Cu-Pb nanocomposites against bearing steel. The sintering temperature and the Pb content as well as the fretting parameters were judiciously selected and varied to investigate the role of microstructure (grain size, second-phase content) on the wear resistance properties of Cu-Pb nanocomposites. A combination of the lowest wear rate (~1.5 × 10^?6 mm³/Nm) and a modest COF (~0.4) was achieved for Cu-15 wt pct Pb nanocomposites. The lower wear rate of Cu-Pb nanocomposites with respect to unreinforced Cu is attributed to high hardness (~2 to 3.5 GPa) of the matrix, Cu₂O/Fe₂O₃-rich oxide layer formation at tribological interface, and exuding of softer Pb particles. The wear properties are discussed in reference to the characteristics of transfer layer on worn surface as well as subsurface damage probed using focused ion beam microscopy. Interestingly, the flash temperature has been found to have insignificant effect on the observed oxidative wear, and alternative mechanisms are proposed. Importantly, the wear resistance properties of the nanocomposites reveal a weak Hall–Petch-like relationship with grain size of nanocrystalline Cu.     

Tribological properties of nanometer cerium oxide as additives in lithium grease

This paper presents a comparative study of the influence of nanometer-CeO_2(nano-CeO_2) and temperature on tribological and lubricating properties of lithium grease. The morphology and structure of nanocrystals were characterized by means of transmission electron microscopy(TEM) and X-ray diffraction(XRD), respectively. Friction and wear tests were conducted on the friction and wear tester.Results show that the lithium grease with addition of nanometer-CeO_2 has much better friction-reducing and anti-wear performance than that of base grease. When the additive in grease is 0.6 wt%, the friction coefficient(COF) and wear scar diameter(WSD) decrease by 28% and 13% comparing with base grease,respectively. The base grease and grease with 0.6 wt% nanometer-CeO_2 both possess the lowest average COF and wear width at 50 ℃. The worn surface morphology after friction test was analyzed by scanning electron microscopy(SEM) and NANOVEA three-dimensional profilometer. Under the lubrication of the lithium grease containing 0.6 wt% nano-CeO_2. few shallow furrows can be observed on the quite smoothed surface and the WSD decreased. Moreover, It was found that the nano-CeO_2 has been incorporated into the surface protective and lubricious layer by energy dispersive spectrometer(EDS) analysis.     

Effects of T4 and T6 Heat Treatments on the Wear Behaviour of WC-Reinforced Mg Alloy Matrix Composite

Collective outcomes of WC particle reinforcement and heat treatment on the dry sliding wear rate of AZ91 magnesium metal matrix composite have been presented. The vacuum-assisted semi-solid stir casting method was employed to fabricate the composites. Wear study was conducted on the specimens using a pin-on-disc tribometer with EN8 steel as a counter material. The experiments were designed using Taguchi L27 array, with control factors viz. applied load (20, 40 and 60 N), sliding speed (1, 2 and 3 m/s), heat treatment (no treatment, T4 and T6) and WC wt% (0, 1.5 and 3). Energy-dispersive X-ray spectroscopy and scanning electron microscopy analyses were performed to study the surface of the tested specimens. T6-treated AZ91/3.0WC composite showed 63% enhanced resistance to wear due to the presence of β-phase (Mg17Al12) precipitation during the heat treatment process and WC reinforcements.     

Secondary Silicon Carbide Formed in the Interaction of Nanosized Silicon Carbide with Iron Oxide

The characteristics of superfine powder composites formed in the interaction of nanosized silicon carbide with iron oxide in vacuum and argon at 1200 and 1400°C, respectively, are analyzed. Silicon carbide (β-SiC), iron silicide and carbide, silicon oxide, and silicon oxynitride are main components of the powder composites. The lattice parameter of SiC in the powder composites synthesized in the SiC–Fe2O3 system is determined. In the interaction in the SiC–Fe2O3 powder mixture in vacuum, secondary SiC is synthesized with a lattice parameter that corresponds to the standard parameter for cubic β-SiC. The interaction in an argon atmosphere is accompanied by the synthesis of secondary SiC with a decreased lattice parameter. The minimum lattice parameter (0.4336 nm) is 0.6% smaller than the standard parameter for cubic β-SiC. The morphology of the powder composite synthesized in the SiC–Fe2O3 system is studied. The average particle size of the powder composite decreases with increasing weight content of secondary SiC.     

Experimental Investigation on Adhesive Wear Behavior of Al–Si6Cu/Ni Coated SiC Composite Under Unlubricated Condition

This paper studies the dry sliding wear behavior of Al–Si6Cu/Ni coated SiC metal matrix composite fabricated using stir casting technique. The SiC reinforcement particles coated with Ni by electroless coating were incorporated at 10-wt% into the metal matrix. The wear behavior was studied on unlubricated pin-on-disc tribometer based on design of experiments modelled using Response Surface Methodology for various sliding parameters such as applied load, sliding velocity and sliding distance. The minimum wear rate condition and optimum condition of the parameters were detected from the developed model. The analysis of variance showed the influence of each parameter on wear rate. The confirmation experiments were done to ensure the validity of the developed regression model. The worn-out surface morphologies of the metal composite were studied using scanning electron microscope analysis. From the experimental results it was found that the parameter which influenced the wear behavior was applied load followed by sliding velocity and distance. The confirmatory experiments confirmed the RSM’s design as precise statistical model in developing regression results with less error. The surface plot of wear characteristics showed that irrespective of the conditions of sliding velocity and distance the wear rate increased on increasing the load. The wear rate exhibited a non linear relationship with sliding velocity and distance. The scanning electron microscopy revealed that higher material deformation was observed at higher load resulting in severe wear of the composite material.     

Effect of SiC and graphite particulates on the damping behavior of metal matrix composites

The effect of SiC and graphite (Gr) particulates on the resultant damping behavior of 6061 A1 metal matrix composites (MMCs) was investigated in an effort to develop a high damping material. The MMCs were processed by a spray atomization and deposition technique and the damping characterization was conducted on a dynamic mechanical thermal analyzer. The damping capacity, as well as the dynamic modulus, was measured at frequencies of 0.1, 1, 10 and 30 Hz over a 30 to 250°C temperature range. The microstructural analysis was performed using scanning electron microscopy, optical microscopy and image analysis. The damping capacity of the 6061 Al/SiC and 6061 Al/Gr MMCs, with two different volume fractions of reinforcements, were compared with that of as-received 6061-T6 Al and spray deposited 6061 Al. It was shown that the damping capacity of 6061 Al could be significantly improved by the addition of either SiC or graphite particulates through spray deposition processing. Finally, the operative damping mechanisms were discussed in light of the data obtained from characterization of microstructure and damping capacity.