Volume Fraction Of SiC Particles Research Articles

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF SICP/AZ91 MAGNESIUM MATRIX COMPOSITES PROCESSED BY STIR CASTING

Magnesium alloy (AZ91) matrix composites reinforced with various volume fractions of SiC-particulates were processed. A Stir casting process has been employed under an inert atmosphere to produce magnesium matrix composites. This process leads to a complete wetting of SiC particles in the molten magnesium. Microstructural feature, such as SiC particles distribution, and the interface between the magnesium matrix and SiC was characterized by scanning electron microscopy (SEM) and energy dispersion X-ray analysis (EDX). The results show a refined matrix structure of the composite compared to the matrix alloy, a uniform SiC distribution in the matrix and that no reaction takes place during the synthesis of the magnesium alloy matrix composites between the oxidized SiC and the molten magnesium. However, AZ91 matrix composite showed a massive formation of ternary intermetallic compound of Mg17 (ZnAl)12 at the SiC interface. The mechanical properties of AZ91 and AZ91-SiC composites have been evaluated and the results are compared with the unreinforced AZ91 alloy. Results of the mechanical properties revealed an increase in hardness value, maximum tensile strength and 0.2 % yielding strength. It was proposed that the strength increase due to SiC addition to AZ91 alloy was a result of a change in the matrix strength, i.e. an increase in dislocation density and a reduction of matrix grain size. However, it is also evident that the strain to failure significantly decreased as the volume fraction of the particulate increased. Examinations of the fracture surface show good bonding between SiC/matrix, extent of fine dimples, matrix cracking and particle cracking.

A Thermodamage Strength Theoretical Model of Ceramic Materials Taking into Account the Effect of Residual Stress

A thermodamage strength theoretical model taking into account the effect of residual stress was established and applied to each temperature phase based on the study of effects of various physical mechanisms on the fracture strength of ultrahigh-temperature ceramics. The effects of SiC particle size, crack size, and SiC particle volume fraction on strength corresponding to different temperatures were studied in detail. This study showed that when flaw size is not large, the bigger SiC particle size results in the greater effect of tensile residual stress in the matrix grains on strength reduction, and this prediction coincides with experimental results; and the residual stress and the combined effort of particle size and crack size play important roles in controlling material strength.

STUDY OF MECHANICAL PROPERTIES AND FRACTURE MODE OF ALUMINA-SILICON CARBIDE NANOCOMPOSITES

In this study Al 2 O 3- SiC nanocomposites have been fabricated by mixing of alumina and silicon carbide nano powders, followed by hot pressing at 1700°C. The mechanical properties and fracture mode of Al 2 O 3- SiC nanocomposites containing different volume fractions (5, 10 and 15%) of nano scale SiC particles were investigated and compared with those of alumina. Al 2 O 3- SiC powders were prepared by planetary milling in isopropanol. Fracture mode of specimens was investigated by means of scanning electron microscopy. Nanocomposites were tougher than alumina when they were hot pressed at the same temperature, and the values of nanocomposite's flexural strength and hardness were higher than those of alumina. Flexural strength, hardness and fracture toughness of the nanocomposites increase by increasing the volume percent of SiC up to 10% and then decrease slightly. The Scanning electron microscopy observations showed that fracture mode changes from intergranular for alumina to transgranular for nanocomposites. Finally X-ray diffraction analysis couldn't detect any chemical reactions between Al 2 O 3 and SiC particles.

Effect of SiC Particle Size on Wear Properties of Al2O3·SiO2/SiC/Mg Hybrid Metal Matrix Composites

The aim of this study was to investigate the effect of SiC particle size on the wear properties of magnesium-based hybrid metal matrix composites (MMCs) reinforced with Saffil short fibers and SiC particles. Hybrid MMCs with different SiC particle sizes of 1, 7, and 20 μm, respectively, were fabricated by the squeeze infiltration process. The volume fractions of Saffil short fibers and SiC particles in the hybrid composites were 15 and 5%, respectively. Wear tests were carried out using a ball-on-disk against a steel ball under the dry sliding condition. The test results showed that the composite with large-sized SiC particles had an improved wear resistance compared with the smaller sized particles.

Microstructure and Mechanical Properties of SIC<sub>P</sub>/MoSi<sub>2 </sub>Composites Manufactured by <i>In Situ</i> Reaction and Hot Pressing

Pure MoSi2 and MoSi2 composites with different volume fraction of SiC particles were prepared by the technology of in situ reaction and hot pressing the pure powder of Mo, Si and C after alcohol mixing. The effects of in situ formed SiC particles on the microstructure, the flexural strength and fracture toughness of SiCP/MoSi2 composites were studied. The research shows the relative density, flexural strength and fracture toughness of the composites are increased compared with those of the pure MoSi2 material. It is found that the in–situ formed SiC particles refine the MoSi2 grains and eliminate the brittle SiO2 glass phase. The strengthening mechanism of the composites is of the refinement of MoSi2 grains,dispersion strengthening of the in–situ formed SiC particles and elimination of the brittle SiO2 glass phase.

An approach for increase of reinforcement content in particle rich zone of centrifugally cast SiCP/Al composites

A cylindrical ingot was produced by means of centrifugal casting using 20 vol.% SiCp/Al composite melt. The melt which was fabricated by double stir-casting method, consisting of three different sizes of SiC particles. SiCp/Al composites were characterized by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD) techniques. The results showed that SiC particles in the 20 vol.% SiCp/Al composite melt migrated towards the outer periphery of the cylindrical ingot under centrifugal force. High reinforcement content SiCp/Al composites were obtained in a zone near the outer periphery of the cylindrical ingot, and the volume fraction of SiC particles reached up to 55%. The thermal expansion test was performed, and the coefficient of thermal expansion (CTE) of the 55 vol.% SiCp/Al composites was found to be 9.9 × 10−6/°C, which was lower than the predicted value based on Kerner’s model and that of 60 vol.% SiCp/Al composites fabricated by conventional processing techniques. This article presented an approach for producing high reinforcement content SiCp/Al composites.

Fabrication of SiC particles-reinforced magnesium matrix composite by ultrasonic vibration

Magnesium matrix composites reinforced with two volume fractions (1 and 3%) of SiC particles (1 μm) were successfully fabricated by ultrasonic vibration. Compared with as-cast AZ91 alloy, with the addition of the SiC particles grain size of matrix decreased, while most of the phase Mg17Al12 varied from coarse plates to lamellar precipitates in the SiCp/AZ91 composites. With increasing volume fraction of the SiC particles, grains of matrix in the SiCp/AZ91 composites were gradually refined. The SiC particles were located mainly at grain boundaries in both 1 vol% SiCp/AZ91 composite and 3 vol% SiCp/AZ91 composite. SiC particles inside the particle clusters may be still separated by magnesium. The study of the interface between the SiC particle and the alloy matrix suggested that SiC particles bonded well with the alloy matrix without interfacial reaction. The ultimate tensile strength, yield strength, and elongation to fracture of the SiCp/AZ91 composites were simultaneously improved compared with that of the as-cast AZ91 alloy.

Microstructure and Mechanical Behaviour of Ultrafine Grained Al-4wt%Cu-(2.5-10) Vol.% SiC Metal Matrix Composites Produced by Powder Compact Forging

Ultrafine grained Al-4wt%Cu-(2.5-10) vol.% SiC metal matrix composite powders were produced from a mixture of Al, Cu and SiC powders using high energy mechanical milling (HEMM). The composite powders produced were first hot pressed at 300°C with a pressure of 240 MPa to produce cylindrical powder compacts with a relative density in the range of 80-94% which decreased with increasing the SiC volume fraction. Powder compact forging was utilized to consolidate the powder compacts into nearly fully dense forged disks. With increasing the volume fraction of SiC from 2.5% to 10%, the average microhardness of the forged disks increased from 73HV to 162HV. The fracture strength of the forged disks increased from 225 to 412 MPa with increasing the volume fraction of SiC particles from 2.5 to 10%. The Al-4wt%Cu-2.5vol.%SiC forged disk did not show any macroscopic plastic yielding, while the Al-4wt%Cu-(7.5 and 10)vol.% SiC forged disk showed macroscopic plastic yielding with a small plastic strain to fracture (~1%).

Manufacturing of Al/SiCp composite foams using calcium carbonate as foaming agent

The aluminium composite foams reinforced by different volume fractions of SiC particles were manufactured with the direct foaming route of melt using different contents of CaCO3 foaming agent. The density of produced foams changed from 0·43 to 0·76 g cm−3. The microstructural features and compressive properties of the Al/SiCp composite foams were investigated. Compressive stress–strain curve of Al/SiCp composite foams is not smooth and exhibits some serrations. At the same relative density of composite foams, the plateau stress of the composite foams increases with increasing volume fraction of SiCp and decreasing weight percentage of CaCO3. The relation between plateau stress, relative density, weight percentage of CaCO3 and SiCp volume fraction of Al/SiCp composite foams with a given particle size was investigated.

Theoretical and experimental study on settling of SiC particles in composite slurries of aluminum A356/SiC

In the present study settling of SiC particles in composite slurries of aluminum A356 alloy/SiC was investigated experimentally and the results were compared with theoretical predictions. The influence of size and volume fraction of SiC particles in different Al/SiC slurries together with thermal history during alloy solidification on the distribution of particles along the height of cylindrical composite samples was studied by image analysis of microstructures. In the theoretical part, the effect of particle shape, agglomeration of particles and hindered settling on the settling velocity of SiC particles was studied by using the Stokes equation with some relevant correction factors. It was found that by using the measured viscosity of slurries in the Stokes equation a good agreement between the experimental results and theoretical predictions could be obtained. A computer program was written using MATLAB software in which the Stokes equation was employed, and in addition to the above-mentioned correction factors, the collision and agglomeration of particles were also considered. This program was able to simulate reasonably accurately the settling of SiC particles in the solidifying alloy.

Effects of Particle Size and Volume Fraction on Extrusion Texture of SiC<sub>p</sub>/Al Metal Matrix Composites

The texture development was investigated in the extruded Al and Al metal matrix composites (MMCs) reinforced with SiC particles of different sizes and volume fractions. During extrusion, both the unreinforced Al and the MMCs develop a strong fiber texture with two components: <111> and <100>. When SiC is introduced into aluminum, the main component of texture is not modified, but the intensity of the component evolves with the volume fraction and average size of SiC particles. For the MMCs reinforced with 3.5μm SiC particles, the texture intensity of the Al matrix tends to decrease as the SiC volume fraction increases, and it is lower than that in the unreinforced Al. However, for the MMCs reinforced with 25 nm and 150 nm SiC particles, the texture intensity of the Al matrix is higher than that in the unreinforced matrix, and it increases with increasing the SiC volume fraction. It is found that superfine particles may introduce some new component into the deformation texture, and the texture intensity increases as the SiC particle size decreases.

Fabrication and Bending Strength of Al/SiC Composites with High Volume Fraction of Reinforcement by Combining Powder Injection Molding and Pressure Infiltration

The paper presents the result of an experimental investigation on the fabrication of Al/SiC composites with high volume fraction of SiC particles by pressure infiltration of liquid aluminum into preforms prepared by powder injection molding (PIM). To obtain the required high particle volume fraction, SiC powders with a bimodal particle size distribution were used. The influence of powder loading and particle size on the bending strength of the prepared composites has been investigated. It is demonstrated that pressure infiltration permits to achieve high relative densities for the composites (i.e. 98.8%). The microstructure studies revealed a uniform distribution of SiC particles in the composites without interface reactions between the particles and the aluminum matrix. The bending strength increases with increasing powder loading and decreasing particle size of the coarse powders in the bimodal powder system.

Reserach on Rheology of Biodegradable Soy Protein Materials

The aluminum metal matrix composites (Al MMCs) reinforced by SiC particles with different sizes (25 nm, 150 nm and 3.5 μm) were fabricated by powder metallurgy technique, and the microstructure and tensile properties of the Al MMCs were investigated. When the volume fraction of SiC particles is fixed to be 5 %, the Al MMCs reinforced by nanosized and submicron particles exhibit much higher ultimate tensile strength and yield strength, and much lower ductility compared with those of the non-reinforced aluminum. However, for the MMC reinforced by 3.5 m SiC particles, almost no strengthening effect is found. The strengthening effect of the Al MMCs is analyzed in terms of dislocation mechanism. Moreover, the tensile fracture surface shows that the damage mechanism of the Al MMCs can be changed as the size of SiC particles is changed.

Effect of SiC Particle Size on Microstructure and Tensile Behavior of Aluminum Matrix Composites

The aluminum metal matrix composites (Al MMCs) reinforced by SiC particles with different sizes (25 nm, 150 nm and 3.5 m) were fabricated by powder metallurgy technique, and the microstructure and tensile properties of the Al MMCs were investigated. When the volume fraction of SiC particles is fixed to be 5 %, the Al MMCs reinforced by nanosized and submicron particles exhibit much higher ultimate tensile strength and yield strength, and much lower ductility compared with those of the non-reinforced aluminum. However, for the MMC reinforced by 3.5 m SiC particles, almost no strengthening effect is found. The strengthening effect of the Al MMCs is analyzed in terms of dislocation mechanism. Moreover, the tensile fracture surface shows that the damage mechanism of the Al MMCs can be changed as the size of SiC particles is changed.

Synthesis and Characterization of Al–SiC Nanocomposites Produced by Mechanical Milling and Sintering

Aluminum powder and various volume fractions of SiC particles with an average diameter of 50 nm were milled by a high-energy planetary ball mill to produce nanocrystalline Al–SiC nanocomposite powders. Double pressing/sintering process was used to consolidate powders to cylindrical specimens. It was shown that a double cycle of cold pressing and sintering can be utilized to obtain high density Al–SiC nanocomposite parts without using a hot-working step. High resolution scanning electron microscopy (HRSEM), X-ray diffraction (XRD) and laser particle size analyzer (PSA) were used to study the morphological and microstructural evolution of nanocomposite powders and bulk samples. The role of volume fraction of SiC nanoparticles in grain size of both as-milled and as-consolidated aluminum matrix was investigated. It was found that the presence of the higher SiC particles eventuate to slowly decrease in grain size of aluminum matrix powders. However, this trend is strongly noticeable in grain size of consolidated samples. The pinning effects on grain stability by SiC nanoparticles were quantitatively analyzed. It was found that Gladman's model is in close agreement with the experimentally determined grain size of Al–SiC nanocomposites.

Investigation of mechanical properties of Cu/SiC composite fabricated by FSP: Effect of SiC particles’ size and volume fraction

In this experiment, copper-base composites reinforced with 30nm and 5μm SiC particles are fabricated on the surface of a purecopper sheetvia friction stir processing (FSP). Microstructure, mechanical properties and wear resistance of friction stir processed (FSPed) materials are investigated as a function of volume fraction of SiC particles. Results show that, applying FSP, without SiC particles, increases the percent elongation significantly (more than 2.5 times) and decreases copper's strength. Adding micro- and nano-sized SiC particles decreases the tensile strength and percent elongation. Increasing the volume fraction or decreasing the reinforcing particle size enhances the tensile strength and wear resistance and lowers the percent elongation.

Volume Fraction Effects of Silicon Carbide on the Wear Behavior of SiC<sub>p</sub>-Reinforced Magnesium Matrix Composites

This paper investigated the volume fraction effect of micro-sized SiC on the tribological behavior of SiCp reinforced AZ91D Mg-based metal-matrix composites (MMCs). The Mg MMCs were prepared by the melt-stirring technique for wear tests. The hardness and coefficient of friction of Mg MMCs increase as increasing volume fraction of SiC particle in MMCs. The SiCp/AZ91D MMCs exhibit superior wear resistance under lower and moderate sliding condition. However, the effects of the SiC particle reinforcements on wear resistance are not as conclusive under severe sliding condition (50N-1500 rpm for all vol.% of MMCs, 50N-1000rpm for 3 vol. % MMCs), since the matrix of MMCs were softened at elevated temperature under such severe condition. However, the incorporation of SiC particles could enhance the wear resistance of AZ91D matrix alloy for most of the sliding conditions.

Effects of SiC Particle and Holding Time on Semi-Solid Microstructure of SiC<sub>P</sub>/AZ61 Composites

Effects of SiC particle and holding time on microstructure evolution of SiCP/AZ61 composites during semi-solid isothermal heat treatment method were studied, and evolution mechanism of semi-solid microstructure of composites was discussed. The results indicated that the process of microstructure evolution of SiCP/AZ61 composites by the isothermal holding at the temperatures of 595°C for different times (0min~90min) experienced in succession the rapid merging of the secondary dendritic arms →large massive structure→melting and separating of the local grain boundary →spheroidization of the gains →slowing growth of globular microstructure. Synthetically, after isothermal holding at 595°C for 30min to 60min the favorable semi-solid microstructure can be obtained; Compared with the monolithic AZ61alloy, microstructure of SiCP/AZ61 composites during semi-solid isothermal heat-treatment was finer as a result of entering of Sic particle, and with the increasing of SiC particle volume fraction, globular gain size was smaller.

Thixotropic compression deformation behavior of SiC p/AZ61 magnesium matrix composites

Compression tests on semi-solid SiC p/AZ61 magnesium matrix composites were carried out using Thermecmastor-Z dynamic material testing machine. Influences of strain-rate, strain, temperature and volume fraction of SiC particles on flow stress were analyzed. The results show that the flow stress of semi-solid SiC p/AZ61 composites is sensitive to temperature and strain rate. The lower the temperature and the larger the strain rate, the higher the flow stress. Meanwhile the flow stress increases with the increase of the volume fraction of SiC particles. This study helps establish the constitutive model of magnesium matrix composites and offers theoretic and experimental references for its thixoforming.

Ultrasonic dissolution of brazing of 55% SiC p/A356 composites

The brazing of 55% SiC p/A356 (volume fraction) composites in air using Zn-Al alloy as a filler metal was investigated. During the brazing process, ultrasonic vibrations were applied to samples for bonding and a significant dissolution of the filler metal into the matrix alloy in the base materials occurred. As brazing temperatures were increased, the thickness of the partial melting layers in the base material increased. SiC particles in the partial melting layer of the base material were transferred into the liquid filler under ultrasonic action and a bond with homogeneously distributed reinforcements was obtained after solidification. The volume fraction of SiC particles in the bonds could be varied by changing the brazing temperature. The maximum SiC particle volume fraction of the bond material reached 37% at a brazing temperature of 500 °C. The shear strength of the brazed bonds was improved at pressures up to 244 MPa (at 20 °C) and increased by 133.8% (at 200 °C) compared with the filler of the Zn-based alloy.