Wear characteristics of hybrid aluminium matrix composites reinforced with graphite and silicon carbide particulates

This investigation studies the dry sliding wear behaviour of Al matrix composites reinforced with Gr and SiC particulate up to 10%, to study the effect of % reinforcement, load, sliding speed and sliding distance on stir cast Al–SiC–Gr hybrid composites, Al–Gr and Al–SiC composites. Parametric studies indicate that the wear of hybrid composites has a tendency to increase beyond% reinforcement of 7.5% as its values are 0.0242 g, 0.0228 g and 0.0234 g respectively at 3%, 7.5% and 10% reinforcement. The corresponding values are 0.0254 g, 0.0240 g and 0.0242 g in Al–Gr composites and 0.0307 g, 0.0254 g and 0.0221 g in Al–SiC composites, clearly indicating that hybrid composites exhibit better wear characteristics. Increase of speed reduces wear and increase of either load or sliding distance or both increases wear. Statistical analysis has revealed interactions among load, sliding speed and sliding distance in composites with Gr particulates.     

铝基碳化硅复合材料超声振动辅助划痕表面形貌研究

为了揭示SiCp/Al复合材料超声振动加工的去除机理,开展针对SiCp/Al复合材料的超声振动辅助划痕(UVAS)和普通划痕对比实验,从划痕形貌方面进行UVAS和普通划痕对比分析。结果表明,普通划痕凹槽处出现大颗粒的破碎,而UVAS凹槽表面则呈现较多的细小碎屑;超声划痕的材料去除率比普通划痕的大。超声振动的引入对改善加工表面形貌有明显作用,是SiCp/Al精密加工的有效方法。     

Friction characteristics of aluminium silicon carbide graphite hybrid composites

Hybrid aluminum metal matrix composites reinforced with silicon carbide (SiC) and graphite (Gr) are extensively used due to high strength and wear resistance. Friction behavior of such hybrid composites is quite vital in deciding the optimal combination of SiC and Gr. The sliding friction response of stir cast hybrid aluminum composites reinforced with equal weight fraction of SiC and Gr particulates of 2.5%, 5%, 7.5% and 10% reinforcement is investigated. The influence of % reinforcement, load, sliding speed and sliding distance on friction coefficient is studied using pin-on-disk equipment with tests based on design of experiments. Hardness of the composites decreases with increase in % reinforcement. Friction coefficient is influenced by sliding speed as well as load and its average value is around 0.269. But, % reinforcement and sliding distance do not affect the friction coefficient.     

Particle effects on friction and wear of aluminium matrix composites

Particle effects on friction and wear of 6061 aluminium (6061 Al) reinforced with silicon carbide (SiC) and alumina (Al₂O₃) particles were investigated by means of Vickers microhardness measurements and scratch tests. Unreinforced 6061 Al matrix alloy was also studied for comparison. To explore the effect of heat treatment, materials subjected to three different heat treatment conditions, i.e. under-aged, over-aged and T6, were used. Multiplescratch tests using a diamond and a steel indentor were also carried out to simulate real abrasive wear processes. Vickers microhardness measurements indicated that T6 heattreated composites had the highest hardness. Single-scratch tests showed that the variation of friction coefficient was similar to that of Vickers hardness and the peak-aged composites exhibited the best wear resistance. The wear rate of fine particle-reinforced composites was mainly affected by hardness. However, the wear rate of large particle-reinforced composites was influenced by both the hardness and fracture of the particles.     

Effect of SiC content and sliding speed on the wear behaviour of aluminium matrix composites

In the present study effect of SiC content and sliding speed on the wear behaviour of aluminium alloy and composite was studied using pin-on-disc apparatus against EN32 steel counterface. These tests were conducted at varying SiC particles in 10, 15 and 25 wt.% and sliding speeds of 0.52, 1.72, 3.35, 4.18 and 5.23 m/s for a constant sliding distance of 5000 m. The results revealed that as the SiC content increases the wear rate and temperature decreases, but reverse trend can be observed for coefficient of friction. All these facts can be discussed on the basis of prevailing wear mechanism.     

Interfacial characteristics of silicon carbide-coated boron-reinforced aluminium matrix composites

The fibre-matrix interfacial region has been examined in BORSIC^®-aluminium. The structure of this interface and that of the silicon carbide-boron interface have been revealed by transmission electron microscopy. Observations of composite fracture surfaces have indicated the considerable strength of the fibre-matrix interface and have shown that interfacial failure is seldom a mode of composite fracture.     

Effect of silicon carbide particulate on cyclic plastic strain response characteristics and fracture of aluminium alloy composites

The cyclic stress-response characteristics of powder-metallurgy-processed high-purity aluminium alloy 2124 discontinuously reinforced with varying volume fractions of silicon carbide particulates were studied over a range of plastic strains. The specimens were cycled using tension/compression loading under total strain control. The composite material, in the heat-treated condition, displayed cyclic hardening at all cyclic strain amplitudes and for different volume fractions of the ceramic reinforcement in the aluminium alloy matrix. The degree of hardening was observed to be greater at the higher cyclic strain amplitudes than at corresponding lower strain amplitudes. Micromechanisms controlling the hardening response during cyclic straining are highlighted and rationale for the observed hardening behaviour is attributed to concurrent and competing influences of an increase in dislocation-dislocation interaction, dislocation multiplication and dislocation-particle interactions, and is a mechanical effect. The kinetics of the cyclic fracture process of the composite alloy is discussed in light of composite microstructural effects, plastic strain amplitude and concomitant response stress.     

Fabrication of carbon fibre-reinforced aluminium composites with hybridization of a small amount of particulates or whiskers of silicon carbide by pressure casting

An investigation was carried out on the fabrication of carbon fibre-reinforced aluminium matrix composites with hybridization of particulates or whiskers of silicon carbide by pressure casting. A small amount of particulates or whiskers was uniformly distributed among carbon fibres and the preforms prepared from the treated fibres were directly infiltrated by molten aluminium under applied stress. It was found that the longitudinal tensile strengths of hybrid composites were greatly improved, although their fibre volume fractions were very low compared to those of conventional composites. With this hybridization method, it is also practical to tailor the fibre volume fraction of composites from 60 to 25 vol %, which is not possible in direct infiltration of fibre preforms by pressure casting. The results obtained lead to the conclusion that particulate or whisker additions act not directly as reinforcements but as promoters to improve the infiltration performances of fibre preforms, and consequently to increase the strength-transfer efficiency of carbon fibres. The addition of particulates or whiskers can also improve other properties of the composites, such as hardness and wear resistance.     

Mechanical and tribological behaviour of nano scaled silicon carbide reinforced aluminium composites

ABSTRACT

This work assesses the impact of the presence of Nano scaled silicon carbide on the Mechanical & Tribological behavior of aluminium matrix composites. Aluminium matrix composites containing 0, 0.5, 1, 1.5, 2 and 2.5 wt.%-nano scaled silicon carbide was set up by a mechanical stirrer. The trial comes about to demonstrate that the inclusion of Nano silicon carbide brings about materials with progressively high elastic modulus and likewise brings about expanded brittle behavior, fundamentally lessening failure strain. Shear modulus and flexural shear modulus likewise increases with silicon carbide increase. The presence of Nano scaled silicon carbide in the aluminium matrix diminishes subsurface fatigue wear and increases wear resistance, because of silicon carbide lubricant activity. Wear testing, microstructure & morphological, density & void testing, hardness, flexural and tensile test of the readied composites were investigated and outcomes were analyzed which demonstrated that including nano-SiC in aluminum (Al) matrix increased wear resistance, tensile strength, and 2 wt. % of nano scaled SiC for Al MMC indicated maximum wear resistance, tensile strength, and an optimum balanced mix of both Tribological and Mechanical properties. Microstructural observation uncovered uniformand homogeneous distribution of SiC particles in the Al matrix.     

Corrosion protection of aluminium-matrix aluminium nitride and silicon carbide composites by anodization

Anodization is an effective surface treatment for improving the corrosion resistance of aluminium-matrix composites. For SiC particle-filled aluminium, anodization was performed successfully in an acid electrolyte, as usual. However, for AlN particle-filled aluminium, anodization needed to be performed in an akaline (0.7 N NaOH) electrolyte instead of an acid electrolyte, because NaOH reduced the reaction between AlN and water, whereas an acid enhanced this reaction. The concentration of NaOH in the electrolyte was critical; too high a concentration of NaOH caused the dissolution of the anodizing product (Al2O3) by the NaOH, whereas too low a concentration of NaOH did not provide sufficient ions for the electrochemical process. The corrosion properties and anodization characteristic of pure aluminium, Al/AlN and Al/SiC were compared. Without anodization, pure aluminium had better corrosion resistance than the composites and Al/SiC had better corrosion resistance than Al/AlN. After anodization, the corrosion resistance of Al/AlN was better than Al/SiC and both composites were better than pure aluminium without anodization, but still not as good as the anodized pure aluminium.     

Superior high-temperature resistance of aluminium nitride particle-reinforced aluminium compared to silicon carbide or alumina particle-reinforced aluminium

Aluminium-matrix composites containing AlN, SiC or Al₂O₃ particles were fabricated by vacuum infiltration of liquid aluminium into a porous particulate preform under an argon pressure of up to 41 MPa. Al/AlN had similar tensile strengths and higher ductility compared to Al/SiC of similar reinforcement volume fractions at room temperature, but exhibited higher tensile strength arid higher ductility at 300–400 °C and at room temperature after heating at 600 °C for 10–20 days. The ductility of Al/AIN increased with increasing temperature from 22–400 °C, while that of Al/SiC did not change with temperature. At 400 °C, Al/AlN exhibited mainly ductile fracture, whereas Al/SiC exhibited brittle fracture due to particle decohesion. Moreover, Al/AlN exhibited greater resistance to compressive deformation at 525 °C than Al/SiC. The superior high-temperature resistance of Al/AlN is attributed to the lack of a reaction between aluminium and AlN, in contrast to the reaction between aluminium and SiC in Al/SiC. By using Al-20Si-5Mg rather than aluminium as the matrix, the reaction between aluminium and SiC was arrested, resulting in no change in the tensile properties after heating at 500 °C for 20 days. However, the use of Al-20Si-5Mg instead of aluminium as the matrix caused the strength and ductility to decrease by 30% and 70%, respectively, due to the brittleness of Al-20Si-5Mg. Therefore, the use of AIN instead of SiC as the reinforcement is a better way to avoid the filler-matrix reaction. Al/Al₂O₃ had lower room-temperature tensile strength and ductility compared to both Al/AlN and Al/SiC of similar reinforcement volume fractions, both before and after heating at 600 °C for 10–20 days. Al/Al₂O₃ exhibited brittle fracture even at room temperature, due to incomplete infiltration resulting from Al₂O₃ particle clustering.     

Silicon nitride matrix composites with unidirectional silicon carbide whisker reinforcement

SiC whisker reinforced Si₃N₄ was fabricated by fiber extrusion and hot pressing. SiC whiskers were unidirectionally oriented in a carrier fiber. The fibers containing the oriented whiskers were hot pressed in Si₃N₄ powder to form a SiC_w/Si₃N₄ composite with approximately 5 volume% whiskers. SEM micrographs were image processed to quantify whisker orientations in the extruded fiber and the composite. Oriented whiskers contributed to nominal increase in fracture strength over monolithic samples before and after thermal shock testing from 500, 600 and 700°C.     

Interactions between tungsten carbide (WC) particulates and metal matrix in WC-reinforced composites

A variety of experimental techniques have been used to investigate the interactions between tungsten carbide (WC–Co 88/12) particulates and the matrix in some new wear resistant cobalt-based superalloy and steel matrix composites produced by hot isostatic pressing. The results show that the chemical composition of the matrix has a strong influence on the interface reaction between WC and matrix and the structural stability of the WC particulates in the composite. Some characteristics of the interaction between matrix and reinforcement are explained by the calculation of diffusion kinetics. The three-body abrasion wear resistance of the composites has been examined based on the ASTM G65-91 standard procedure. The wear behavior of the best composites of this study shows great potential for wear protection applications.     

Effect of a high-temperature cycle on the mechanical properties of silicon carbide/titanium metal matrix composites

The effects of fibre/matrix interface strength and thermal residual stresses on the mechanical properties of a silicon carbide/titanium composite were investigated. A 3-ply [0/90/0] composite was subjected to a simulated superplastic forming/diffusion bonding (SPF/DB) temperature cycle which changed fibre/matrix interfacial strength and thermal residual stresses in the composite. The [0/90/0] composite subjected to the SPF/DB process showed a 25% decrease in ultimate tensile strength (UTS) and a 30% decrease in failure strain compared to the as-fabricated (ASF) material. The fatigue life for the SPF/DB specimens was approximately 50% lower than the ASF specimens. The fracture surface of the ASF specimens was very irregular accompanied by substantial fibre pull-out as compared to the planar fracture surface of the SPF/DB cycled specimens that showed negligible fibre pull-out. The large changes in the tensile strength and fatigue life due to the SPF/DB cycle are explained by a difference in the failure mechanisms occurring as a result of the SPF/DB-induced changes in the strength of the fibre/matrix interface and higher thermal residual stresses. Unreinforced titanium was also tested to study the effect of the SPF/DB cycle on the matrix static properties. Fibres were etched from the composite and then individually tested for modulus and strength. Finally, a microscopic examination of the fibre/matrix interface was performed to study the effects of the SPF/DB cycle on the interface.     

Microstructural characterization of a silicon carbide whisker reinforced 2124 aluminium metal matrix composite

The microstructure of a silicon carbide whisker (SiC_w) reinforced 2124 aluminium metal matrix composite was characterized using scanning transmission electron microscopy (STEM). The SiC whiskers ranged in length from approximately 2 to 10 µm, and demonstrated good bonding to the aluminium matrix. In a few cases, the interface between SiC whiskers and the aluminium matrix exhibited wavy characteristics. The size of subgrains in the aluminium matrix was found to be dependent upon that of SiC whiskers. In addition, two types of intermetallic compounds were observed in the composite.     

Effect of matrix alloy and influence of SiC particle on the sliding wear characteristics of aluminium alloy composites

This article presents an effect of matrix alloy and influence of SiC particle on the sliding wear characteristics of high strength aluminium alloys AA7010, AA7009 and AA2024, composites was examined under varying applied pressure and a fixed sliding speed of 3.35 m/s. The results revealed that the wear resistance of the composite was noted to be significantly higher than that of the alloy and is suppressed further due to addition of SiC particles. The overall observation among the matrix alloys, AA7010 alloy shows maximum wear resistance than that of the other, and can withstand the seizure pressure up to 2.6 MPa. The wear mechanism was studied through worn surfaces and microscopic examination of the developed wear tracks. The wear mechanism strongly dictated by the formation and stability of oxide layer, mechanically mixed layer (MML) and subsurface deformation and cracking. The overall results indicate that the high strength aluminium alloys and composite could be considered as an excellent material where high strength and wear resistance components are prime importance especially designing for structural applications in aerospace and general engineering sectors.     

Computation of radar absorbing silicon carbide foams and their silica matrix composites

SiC-foams and their composites were studied as novel stealthy materials by numerical simulations. The reflection coefficients of various SiC-foams are found to be strongly dependent on the SiC volume fractions, electric conductivities and frequency. A foaming SiC allows to reach high level of electromagnetic wave absorbing ability when the SiC volume fraction and the conductivity at proper values comparing to SiC-particles and SiC-bulk, Which due to an increase of electromagnetic energy dissipation in foaming structures and an improvement of the conjugation condition with free space. It is of most importance that SiC-foams exhibit artificial magnetic properties that can absorb the magnetic energy of electromagnetic waves. The electromagnetic absorbability of the silica composites are significantly decreased compared to that of the SiC-foams alone for the larger impedance mismatch with free space.