Dry sliding wear behaviour of a novel 6351 Al-Al4SiC4 composite at high loads

In this research work the dry sliding wear behaviour of 6351 Al alloy and 6351 Al based composites possessing varying amount of (2–7 vol%) insitu Al₄SiC₄ reinforcement was investigated at low sliding speed (1?m?s^?1) against a hardened EN 31 disk at higher loads (44 N and 68.7 N). In general, at higher loads, the wear mechanism involved microcutting and microploughing abrasion. In most occasions, Al₄SiC₄ reinforced 6351 Al based composites exhibited much higher wear rate (lower wear resistance) than the unreinforced 6351Al alloy. This was mainly attributed to the removal of reinforcement particle through microcutting abrasion process that resulted in cavitation and subsequent microploughing abrasion for rapid removal of material from surface. This is on contrary to the author's previous research work, where at lower loads (24.5 N or below), Al₄SiC₄ particles stood tall to enhance wear resistance of 6351 Al-Al₄SiC₄ composite.     

Evaluation of Abrasive Wear Resistance of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/7075 Composite by Taguchi Experimental Design Technique

Two-body abrasive wear resistance of 7075 Al-alloy reinforced with 20 wt% Al₂O₃ particles has been studied with reference to unreinforced base alloy by design of experimental technique. Taguchi L₉ orthogonal array and analysis of variance techniques considering four factors, i.e., load, size of SiC abrasive particle, velocity and sliding distance, each at three different levels, have been employed. The experimental results reveal that wear resistance of composite is far superior than that of the unreinforced base alloy under any given test condition. In general, the most dominating factor is found to be the size of abrasive particle followed by load for both base alloy and composite. The confirmation tests reveal the accuracy level ±?5.52 and ±?6.06% for base alloy and composite, respectively. Mechanism of abrasive wear and the difference of wear response of base alloy and composite are discussed via characterizations of worn surface and generated wear debris.     

Dry sliding wear behavior of plasma-sprayed aluminum hybrid composite coatings

Al-SiC _p composite and Al-SiC _p -C _p hybrid composite coatings were produced by plasma spraying of premixed powders onto A356 alloy substrates. Four composite coatings, Al+20 vol pct SiC _p , Al+20 vol pct SiC _p +C _p , Al+40 vol pct SiC _p , and Al+40 vol pct SiC _p +C _p , were obtained. The dry sliding wear behavior of these coatings and pure aluminum have been studied at a sliding velocity of 1 m/s in the applied-load range of 25 to 150 N (corresponding to a normal stress of 0.5 to 3 MPa). The composite coatings had a significantly improved wear resistance over pure Al. The composite coatings with a higher SiC _p content of 40 vol pct exhibited superior wear resistance than those with a lower SiC _p content of 20 vol pct. The presence of graphite particles had different influences on the wear resistance, depending on the applied load. At lower loads, graphite improved the wear resistance considerably. At higher loads, the wear resistance of the hybrid composite coatings was similar to that of the composite coatings without graphite particles. At lower loads, an oxidative wear mechanism was dominant. At higher loads, delamination was a major wear mechanism. Graphite particles did not change their wear mechanism at the same applied loads.     

Friction and abrasion resistance of cast aluminum alloy-fly ash composites

The abrasive wear properties of stir-cast A356 aluminum alloy-5 vol pct fly ash composite were tested against hard SiC _p abrasive paper and compared to those of the A356 base alloy. The results indicate that the abrasive wear resistance of aluminum-fly ash composite is similar to that of aluminum-alumina fiber composite and is superior to that of the matrix alloy for low loads up to 8 N (transition load) on a pin. At loads greater than 8 N, the wear resistance of aluminum-fly ash composite is reduced by debonding and fracture of fly ash particles. Microscopic examination of the worn surfaces, wear debris, and subsurface shows that the base alloy wears primarily by microcutting, but the composite wears by microcutting and delamination caused by crack propagation below the rubbing surface through interfaces between fly ash and silicon particles and the matrix. The decreasing specific wear rates and friction during abrasion wear with increasing load have been attributed to the accumulation of wear debris in the spaces between the abrading particles, resulting in reduced effective depth of penetration and eventually changing the mechanism from two-body to three-body wear, which is further indicated by the magnitude of wear coefficient.     

Correlation of microstructure and abrasive and sliding wear resistance of (TiC,SiC)/Ti-6Al-4V surface composites fabricated by high-energy electron-beam irradiation

This study is concerned with the correlation of microstructure and abrasive and sliding wear resistance of (TiC,SiC)/Ti-6Al-4V surface composites fabricated by high-energy electron-beam irradiation. The mixtures of TiC, SiC, Ti + SiC, or TiC+SiC powders and CaF₂ flux were deposited on a Ti-6Al-4V substrate, and then an electron beam was irradiated on these mixtures. The surface composite layers of 1.2 to 2.1 mm in thickness were homogeneously formed without defects and contained a large amount (30 to 66 vol pct) of hard precipitates such as TiC and Ti₅Si₃ in the martensitic matrix. This microstructural modification, including the formation of hard precipitates in the surface composite layer, improved the hardness and abrasive wear resistance. Particularly in the surface composite fabricated with TiC + SiC powders, the abrasive wear resistance was greatly enhanced to a level 25 times higher than that of the Ti alloy substrate because of the precipitation of 66 vol pct of TiC and Ti₅Si₃ in the hardened martensitic matrix. During the sliding wear process, hard and coarse TiC and Ti₅Si₃ precipitates fell off from the matrix, and their wear debris worked as abrasive particles, thereby reducing the sliding wear resistance. On the other hand, needle-shaped Ti₅Si₃ particles, which did not play a significant role in enhancing abrasive wear resistance, lowered the friction coefficient and, accordingly, decelerated the sliding wear, because they played more of the role of solid lubricants than as abrasive particles after they fell off from the matrix. These findings indicated that high-energy electron-beam irradiation was useful for the development of Ti-based surface composites with improved abrasive and sliding wear resistance, although the abrasive and sliding-wear data should be interpreted by different wear mechanisms.     

Influence of Al4C3 Particles on Grain Refinement of Mg–3Al Alloys

Al?CSi/Al₄C₃ master alloy has been developed by reacting the SiC particles in Al melt. The extent of SiC conversion to Al₄C₃ in the Al?CSi/Al₄C₃ master alloy has been calculated using optical emission spectroscopy. Experimental results indicated that only 70?% of SiC particles have been converted into Al₄C₃ after the reaction between Al and SiC in Al/5?wt% SiC_p composites at 900?°C. The grain refining efficiency of Al?CSi/Al₄C₃ master alloy has been assessed by adding this into the Mg?C3Al alloy. Grain size of Mg?C3Al alloy has been significantly refined from 480 to 220???m by the addition of 0.07?wt% of Al₄C₃ particles in the form of Al?CSi/Al₄C₃ master alloy.     

Characterization and tribological behavior of cast In-Situ Al (Mg,Mo)-Al2O3 (MoO3) composite

Aluminum alloy—based cast in-situ composite has been synthesized by dispersion of externally added molybdenum trioxide particles (MoO₃) in molten aluminum at the processing temperature of 850 °C. During processing, the displacement reaction between molten aluminum and MoO₃ particles results in formation of alumina particles in situ and also releases molybdenum into molten aluminum. A part of this molybdenum forms solid solution with aluminum and the remaining part reacts with aluminum to form intermetallic phase Mo(Al_1−x Fe _x )₁₂ of different morphologies. Magnesium (Mg) is added to the melt in order to help wetting of alumina particles generated in situ, by oxidation of molten aluminum by molybdenum trioxide, and helps to retain these particles inside the melt. The mechanical properties of the cast in-situ composite, as indicated by ultimate tensile stress, yield stress, percentage elongation, and hardness, are relatively higher than those observed either in cast commercial aluminum or in cast Al-Mo alloy. The wear and friction of the resulting cast in-situ Al(Mg,Mo)-Al₂O₃(MoO₃) composites have been investigated using a pin-on-disc wear testing machine under dry sliding conditions at different normal loads of 9.8N, 14.7N, 19.6N, 24.5N, 29.4N, 34.3N, and 39.2 N and a constant sliding speed of 1.05 m/s. The results of the current investigation indicate that the cumulative volume loss and wear rate of cast in-situ composites are significantly lower than those observed either in cast commercial aluminum or in cast Al-Mo alloy, under similar load and sliding conditions. Beyond about 30 to 35 N loads, there appears to be a higher rate of increase in the wear rate in the cast in-situ composite as well as in cast commercial aluminum and cast Al-Mo alloy. For a given normal load, the coefficient of friction of cast in-situ composite is significantly lower than those observed either in cast commercial aluminum or in cast Al-Mo alloy. The coefficient of friction of cast in-situ composite increases gradually with increasing normal load while those observed in cast commercial aluminum or in cast Al-Mo alloy remain more or less the same. Beyond a critical normal load of about 30 to 35 N, the coefficient of friction decreases with increasing normal load in all the three materials.     

Effect of microstructure (particulate size and volume fraction) and counterface material on the sliding wear resistance of particulate-reinforced aluminum matrix composites

The effects of microstructure (namely, particulate volume fraction and particulate size) and the counterface materials on the dry-sliding wear resistance of the aluminum matrix composites 2014A1-SiC and 6061Al-Al₂O₃ were studied. Experiments were performed within a load range of 0.9 to 350 N at a constant sliding velocity of 0.2 ms^-1. Two types of counterface materials, SAE 52100 bearing steel and mullite, were used. At low loads, where particles act as loadbearing constituents, the wear resistance of the 2014A1 reinforced with 15.8 μm diameter SiC was superior to that of the alloy with the same volume fraction of SiC but with 2.4 μm diameter. The wear rates of the composites worn against a steel slider were lower compared with those worn against a mullite slider because of the formation of iron-rich layers that act asin situ solid lubricants in the former case. With increasing the applied load, SiC and A1₂O₃ particles fractured and the wear rates of the composites increased to levels comparable to those of unreinforced matrix alloys. The transition to this regime was delayed to higher loads in the composites with a higher volume percentage of particles. Concurrent with particle fracture, large strains and strain gradients were generated within the aluminum layers adjacent to contact surfaces. This led to the subsurface crack growth and delamination. Because the particles and interfaces provided preferential sites for subsurface crack initiation and growth and because of the propensity of the broken particles to act as third-body abrasive elements at the contact surfaces, no improvement of the wear resistance was observed in the composites in this regime relative to unreinforced aluminum alloys. A second transition, to severe wear, occurred at higher loads when the contact surface temperature exceeded a critical value. The transition loads (and temperatures) were higher in the composites. The alloys with higher volume fraction of reinforcement provided better resistance to severe wear. Wearing the materials against a mullite counterface, which has a smaller thermal conductivity than a counterface made of steel, led to the occurrence of severe wear at lower loads.     

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.     

Investigation on Mechanical and Adhesive Wear Behavior of Centrifugally Cast Functionally Graded Copper/SiC Metal Matrix Composite

The objective of this work is to fabricate functionally graded unreinforced copper alloy (Cu–10Sn) and a Cu–10Sn/SiC composite (Ø_out100 × Ø_in70 × 100 mm) by horizontal centrifugal casting process and to investigate its mechanical and tribological properties. The microstructure and hardness was analysed along the radial direction of the castings; tensile test was conducted at both inner and outer zones. Microstructural evaluation of composite indicated that the reinforcement particles formed a gradient structure across the radial direction and maximum reinforcement concentration was found at the inner periphery. Hence maximum hardness (205 HV) was observed at this surface. Tensile test results showed that, the tensile strength at inner zone of composite was observed to be higher (248 MPa) compared to that of the outer zone and unreinforced alloy. As mechanical properties showed better results at inner periphery, dry sliding wear experiments were carried out on the inner periphery of composite using pin-on-disc tribometer. Process parameters such as load (10–30 N), sliding distance (500–1500 m) and sliding velocity (1–3 m/s) were analyzed by Taguchi L₂₇ orthogonal array. The influence of parameters on wear rate was analyzed by signal-to-noise ratio and analysis of variance. Analysis results revealed that load (54%) had the highest effect on wear rate followed by sliding distance (18.2%) and sliding velocity (3.7%). The wear rate of composite increased with load and sliding distance, but decreased with sliding velocity. Regression equation was developed and was validated by confirmatory experiment. Worn surface of composite was observed using scanning electron microscopy and transition of wear was observed at all extreme conditions.     

Measurement of residual strain in An AlSiCw composite using convergent-beam electron diffraction

Residual strains were introduced into an AlSiC_w composite by in situ cooling a thin foil from room temperature to -160°C. A detailed analysis was conducted using convergent-beam electron diffraction (CBED) to quantify the elastic residual stresses and strains in the matrix near the end and side of a SiC whisker. Large hydrostatic and effective stresses were measured in the matrix near the side of the whisker; the maximum stresses were located near the Al/SiC_w interface and decreased to zero approximately 1 μm (∼2 whisker diameters) from the interface. Residual strains were also observed in the matrix near the whisker end, but these strains could not be measured due to the complexity of the strain field. At the whisker end, the largest residual strains were located near the Al/SiC_w interface and decreased to zero approximately 0.5 μm (∼1 whisker diameter) from the interface. Finite element techniques were used to predict the residual strains in the composite material and these results were compared to experimental measurements.     

Mechanical and Wear Properties of Al–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Metal Matrix Composites Fabricated by the Combined Effect of Stir and Squeeze Casting Method

The effects of nano particles on double shear strength and tribological properties of A356 alloy reinforced with Al₂O₃ nano particles of size 30 nm were investigated. The percentage inclusions of Al₂O₃ were varied from 0.5 to 1.5 wt%. The particles were added with stirring at 400 rpm and squeeze casting at 750 °C and pressure of 600 MPa in a squeeze casting machine. Comparison of the performance of as cast samples of A356/Al₂O₃ nano composite was conducted. The tribological properties of the samples were also investigated by pin-on-disk tests at 10, 30 and 50 N load, sliding speed 0.534 m/s and sliding distance 1100 m in dry condition. SEM images of microstructure analysis of the composite, Al₂O₃ (0.5 and 1 %) particles were well dispersed in the A356 alloy matrix. Partial agglomeration was observed in metal matrix composite with higher (1.5 %) Al₂O₃ particle contents. The nano dispersed composites containing 0.5 and 1 wt% of Al₂O₃ nano particles exhibited the highest double shear strength, lesser wear loss and coefficient of friction.     

Solid particle erosion of Al alloy and Al-alloy composites: Effect of heat treatment and angle of impingement

Erosive wear behavior of the as-cast and heat-treated Al alloy and the Al-alloy-SiC particle composite against Al₂O₃ erodent has been examined at different angles of impingement (15 to 90 deg). It has been noted that the cast Al alloy exhibited a higher erosion rate than the heat-treated alloy and composites irrespective of the angle of impingement. It is noted that the as-cast and heat-treated Al alloy exhibited a maximum wear rate at the 45 deg angle of impingement, whereas the composite, in as-cast as well as in heat-treated conditions, showed a maximum erosion rate at the 60 deg angle of impingement. Subsurface studies of the alloy and composite confirm that the material loss, during erosive wear, is primarily due to microcutting/microplowing (i.e., abrasive-type) and microfracture (i.e., impact-type) actions. At a low angle of impingement, the abrasive type is the dominating factor for material removal, and at a higher angle of impingement, both the impact-type and abrasive-type actions play critical roles. The impact type is mainly localized at the tip of the erosion profile, while the abrasive type takes place along the sidewalls of the profile. This is explained on the basis of the erosion mechanism using a schematic diagram.     

Dry sliding wear behavior of A356-15 Pct SiC p composites under controlled atmospheric conditions

The present investigation was carried out to provide a deeper insight into the mechanism of wear behavior of A356-15 vol pct SiC _p composite under controlled argon and oxygen atmospheres through a detailed characterization of worn surfaces and subsurfaces. Dry sliding wear tests were performed for both as-cast and T6-treated specimens using a pin-on-disc machine with three sliding velocities (0.5, 1, and 2 ms⁻¹) and three loads (1, 2, and 3 MPa). The wear rate of A356-15 vol pct SiC _p composite was lower by nearly one order of magnitude under argon atmosphere compared to the specimens tested under oxygen atmosphere for all experimental conditions. Under argon atmosphere, the mechanism of material removal was by delamination wear and did not change within the parametric regime. In the case of the specimen tested under oxygen atmosphere, the wear behavior of the composite depended on the experimental conditions. At low load and low sliding velocity, the material removal was by abrasion. While at high load and high sliding velocity, the material removal mechanism was by delamination wear. Further, the mechanical mixed layer (MML) formed under argon atmosphere was more stable and homogenous compared to that formed under oxygen atmosphere. The MML formed under both atmospheres revealed much less in Fe content.     

Effect of iron (Wt.%) on adhesive wear response of Al-12Si-1Cu-0.1Mg alloy in dry sliding conditions

The presence of iron leads to different types of intermetallics in Al-Si alloys, among them needle shaped β-phase (Al₅FeSi) can lead to variations in hardness of the Al-Si alloy which ultimately can affect the wear resistance of the alloy. In this paper, the effect of iron on wear behavior of cast Al-Si alloys has been reported. Sliding wear behavior of eutectic alloy Al-12Si-1Cu-0.1Mg was investigated in dry sliding conditions by using pin-on-disk test configuration against heat treated EN31 steel counter-surface at room temperature. Sliding wear behavior has been evaluated at four normal loads of 5, 20, 50 and 70 N and two sliding speeds, 2 m/s and 4 m/s. Worn pin surfaces were examined by scanning electron microscopy (SEM) for analyzing wear mechanisms. The wear mechanism has been found to be mild oxidative type at lower sliding speed of 2m/s for entire range of loads used in the study. Transition to severe metallic wear occurs at higher sliding speed of 4 m/s at normal load of 5 N. Hardness of the alloy increased with increase in iron addition primarily due to presence of needle shaped Fe-rich intermetallics but it leads to an increased wear rate.     

Analysis of interfacial shear strength of SiC fiber reinforced 7075 aluminum composite by pushout microindentation

The interfacial shear strength of continuous silicon carbide fiber reinforced 7075 aluminum matrix composite (SiC_f/7075Al) has been investigated in this research by pushout microindentation. The SiC_f/7075Al composite specimens were processed by diffusion bonding alternate layers of SiC fibers and 7075Al alloy plates. From the measured stress-displacement curves of indentation tests, the interfacial shear strengths of the composite specimens were obtained, and the stress-displacement curves were basically divided into two regions: (1) elastic deformation and (2) interface decohesion and fiber sliding. With increasing aging time, the interfacial shear strength of the composite increased to 167 MPa for T6-treated specimens, and the variation of the interfacial shear strength well followed that of the ultimate tensile strength of 7075Al matrix alloy. With decreasing specimen thickness, the interfacial shear strength of the composite and the amplitude of stress fluctuation slightly decreased because of the stress relaxation effect near specimen surfaces. Under higher indentation velocities, both the interfacial shear strength and the amplitude of stress fluctuation became smaller.     

电弧喷涂含陶瓷颗粒铝基复合涂层的微结构和性能

采用5052半硬铝带分别包覆Al_2O_3、SiC、B_4C、TiC陶瓷颗粒制备的粉芯丝材进行电弧喷涂试验,制备了含陶瓷颗粒的铝基复合涂层。利用光学显微镜、XRD分析了涂层的微观组织和相结构,测试了复合涂层的显微硬度、耐磨性及耐腐蚀性。研究结果表明,制备的铝基复合涂层中含有一定数量的未熔陶瓷颗粒,涂层较为致密,无明显缺陷。含陶瓷铝基涂层的物相主要由Al和所添加的陶瓷相构成,其中在含B_4C陶瓷涂层中还存在Al_3BC、Al_4C_3和AlB_2等新相。陶瓷颗粒的加入有利于提高铝基复合涂层的显微硬度,其中B_4C的加入使涂层中基体相显微硬度提高了1.5倍,这是由于B_4C陶瓷和Al反应生成Al_3BC、Al_4C_3和AlB_2硬质相。复合涂层的耐磨性均优于纯铝涂层,摩擦磨损的形式主要为粘着磨损。动电位极化腐蚀试验表明,含SiC和TiC陶瓷涂层具有较低的腐蚀电流,耐蚀性较好,含SiC陶瓷的复合涂层出现了明显的钝化现象。     

A comparative study on abrasive wear behavior of semisolid–liquid processed Al–Si matrix reinforced with coated B4C reinforcement

A comparative study on abrasive wear behavior of the sol?Cgel coated B₄C particulate reinforced aluminum metal matrix composite has been carried out in the present investigation. In general, composites offer superior wear resistance as compared to the alloy irrespective of applied load and B₄C particles volume fraction. This is primarily due to the presence of the hard dispersoid which protects the matrix from severe contact with the counter surfaces, and thus results in less wear, lower coefficient friction and temperature rise in composite as compared to that in the alloy. The wear sliding test disclosed that the weight loss of the coated B₄C reinforced composites decreases with increasing volume fraction of B₄C particulates. The wear rate in all the samples increases marginally with applied load prior to reaching the critical load. It is ascribed to the increase in fracture of reinforcement, the penetration of hard asperities of the counter surface into the softer pin surface and micro cracking tendency of the subsurface. After the critical load there is a transition from smooth linear increase wear rate to sudden increase in wear rate. This is attributed to the significantly higher frictional heating and thus the localized adhesion and softening of the surface with the counter surface.     

An analysis of thermal residual stresses in Ti-6-4 alloy reinforced with SiC and Al2O3 fibres

Thermal residual stresses in Ti6Al4V alloy reinforced with silicon carbide (SiC) and sapphire alumina (Al₂O₃) fibres are estimated based on an elastic-viscoplastic micromechanics analysis. Effects of fibre volume fraction and different manufacturing procedures are considered and comparisons made with published experimental results for the SiC fibre composite. Stress components in the Ti-6-4/Al₂O₃ are generally less than half the corresponding values in the Ti-6-4/SiC composite.     

Enhancement of Tribological Properties of Al 6060 by Spray Coated TiO<Subscript>2</Subscript> Nanoparticle

Al 6060 alloy was coated with TiO₂ by spray pyrolysis technique at 400 °C using Titanium isopropoxide as precursor. The adhesion of the coating with the alloy was enhanced by annealing at 450 °C for 1 h which increased the hardness by 50%. Dry sliding wear resistance was experimented based on Taguchi’s L₂₇ array using pin-on-disc tribometer by varying parameters such as applied load (15, 25 and 35 N), sliding distance (500, 1000 and 1500 m) and sliding velocity (1.5, 2.5 and 3.5 m/s). Analysis of Variance predicted the major influence by load, followed by velocity and distance. Trend depicted an increase in wear rate with load and distance, whereas with velocity it decreased initially and then increased. Optimum condition for maximum wear resistance was determined from the Signal-to-Noise ratio. Experimental results were validated using regression equation with an error less than 3%. Scanning Electron Microscope analysis of the worn surfaces had revealed more defoilage and lay-off as the applied load was increased.