Volume Fraction Of SiC Particles Research Articles

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.

Comportamiento a la corrosión electroquímica de aleaciones MgAl con recubrimientos de materiales compuestos Al/SiCp mediante proyección térmica

The corrosion protection of Mg-Al alloys by flame thermal spraying of Al/SiCp composite coatings was evaluated by electrochemical impedance spectroscopy in 3.5 wt.% NaCl solution. The volume fraction of SiC particles (SiCp) varied between 5 and 30%. The as-sprayed Al/SiCp composite coatings revealed a high number of micro-channels, largely in the vicinity of the SiC particles, that facilitated the penetration of the electrolyte and the subsequent galvanic corrosion of the magnesium substrates. The application of a cold-pressing post-treatment reduced the degree of porosity of the coatings and improved the bonding at the coating/substrate and Al/SiC interfaces. This resulted in improved corrosion resistance of the coated specimens. The effectiveness of the coatings slightly decreased with the addition of 5-30 vol.% SiCp compared with the unreinforced thermal spray aluminium coatings.

Influence of size and volume fraction of SiC particulates on properties of ex situ reinforced Al–4.5Cu–3Mg metal matrix composite prepared by direct metal laser sintering process

Direct metal laser sintering (DMLS) process has a great potential to prepare metal matrix composites (MMCs) in fabrication of arbitrary shaped jobs through rapid manufacturing. In the present work, silicon carbide particulates reinforced aluminium based metal matrix composite was developed by direct metal laser sintering process. Influences of SiC particulate (SiCp) on density, porosity and microhardness of the composite were investigated. It shows that SiCp having 300 mesh size provides higher density and lower porosity because of lower clustering effect. Higher microhardness was achieved at 1200 mesh of reinforcement because of lower grain size. Microhardness increases with increase of volume fraction of SiCp and higher value was achieved at high reinforcement content of 30vol.%. Microstructure was studied through scanning electron microscopy (SEM) and X-ray elemental mapping. Interfacial microstructure was also investigated and cracks were found in number of cases due to difference between co-efficient of thermal expansion of matrix alloy and SiCp.

Experimental approach and modelling of the mechanical behaviour of graphite fuel elements subjected to compression pulses

Among the activities led by the Generation IV International Forum (GIF) relative to the future nuclear systems, the improvement of recycling of fuel elements and their components is a major issue. One of the studied systems by the GIF is the graphite-moderated high-temperature gas cooled reactor (HTGR). The fuel elements are composed of fuel roads half-inch in diameter named compacts. The compacts contain spherical particles made of actinide kernels about 500 m in diameter coated with three layers of carbon and silicon carbide, each about 50 m thick, dispersed in a graphite matrix. Recycling of compacts requires first a separation of triso-particles from the graphite matrix and secondly, the separation of the triso-coating from the kernels. This aim may be achieved by using pulsed currents: the compacts are placed within a cell filled by water and exposed to high voltage between 200 – 500 kV and discharge currents from 10 to 20 kA during short laps of time (about 2 µs) [1-2]. This repeated treatment leads to a progressive fragmentation of the graphite matrix and a disassembly of the compacts. In order to improve understanding of the fragmentation properties of compacts a series of quasi-static and dynamic experiments have been conducted with similar cylindrical samples containing 10% (volume fraction) of SiC particles coated in a graphite matrix.

Effects of volume fraction of SiC particles on mechanical properties of SiC/Al composites

SiC particle reinforced pure aluminum composites were fabricated using a powder metallurgy method. The effect of the volume fraction of the SiC particles on the mechanical properties of the composites was studied by both model simulation and experiment. The results indicate that the yield strength and tensile strength increase, but the elongation decreases with the increase in the volume fraction of the SiC particles. Both the modified shear lag model and the multi-scale model predicted yield strength and normalized elongation show similar evolution trends with the experimental data. However, the modified shear lag model underestimates the yield strength due to the ignorance of the strengthening mechanisms caused by grain refinement and dislocations interaction by the introduction of the SiC particles, and the multi-scale model overestimates the normalized elongation due to the ignorance of the pores distributed in the matrix.

Microstructural characteristics and properties in centrifugal casting of SiC p/Zl104 composite

The microstructural characteristics and Brinell hardness of a cylinder produced by centrifugal casting were investigated using 20% (volume fraction) SiC p/Zl104 composites. Macrostructure and XRD analysis show that most of SiC particles segregate to the external circumference of the cylinder, the other SiC particles maintain in the inner circumference of the cylinder, and a free particle zone is left in the middle circumference of the cylinder. Microstructural characteristics and quantitative assessment of SiC particles show that most of congregated SiC particles in 20%SiC p/Zl104 composites are dispersed by centrifugal force, and the other congregated SiC particles and most of alumina oxide are segregated to the inner circumference of the cylinder. The SiC particles in aluminum melt can promote the refinement of primary α(Al) during solidification, and fine primary α(Al) grains can also promote the uniform distribution of SiC particles. Brinell hardness of SiC p/Zl104 composites is connected with not only the volume fraction of SiC particles, but also the distribution of SiC particles in matrix alloy.

The Sensitivity of Strain Rate and Size Effect with Different Particle Volume Fraction in SiCp/Al Composite

In this paper the sensitivity of strain rate and size effect with different particle volume fraction in SiCp/Al Composite were studied through the experiment. Specimens with 40% and 30% SiC particle volume fraction were made. There are three types of particle sizes in each volume fraction. The sensitivity of strain rate and the effect of particle size in Al matrix composites reinforced with the different volume fraction were investigated, using the split Hopkinson pressure bar and Instron5882 universal material testing machine. The surface microstructure of the specimens in each composite was examined using optical microscopy and SEM. Through the strain-stress curves, the sensitivity of strain rate can be obtained. The experimental results show that the sensitivity of strain rate increases with the increasing of particle volume fraction. At the same volume fraction, the size effect were observed obviously and higher flow stresses were obtained in the composites reinforced with small particles than that in the composite with large particles.

Dry sliding wear behaviour of magnesium alloy based hybrid composites in the longitudinal direction

In the present investigation, the wear behaviour of a creep-resistant AE42 magnesium alloy and its composites reinforced with Saffil short fibres and SiC particles in various combinations is examined in the longitudinal direction i.e., the plane containing random fibre orientation is perpendicular to the steel counter-face. Wear tests are conducted on a pin-on-disc set-up under dry sliding condition having a constant sliding velocity of 0.837 m/s for a constant sliding distance of 2.5 km in the load range of 10–40 N. It is observed that the wear rate increases with increase in load for the alloy and the composites, as expected. Wear rate of the composites is lower than the alloy and the hybrid composites exhibit a lower wear rate than the Saffil short fibres reinforced composite at all the loads. Therefore, the partial replacement of Saffil short fibres by an equal volume fraction of SiC particles not only reduces the cost but also improves the wear resistance of the composite. Microstructural investigation of the surface and subsurface of the worn pin and wear debris is carried out to explain the observed results and to understand the wear mechanisms. It is concluded that the presence of SiC particles in the hybrid composites improves the wear resistance because these particles remain intact and retain their load bearing capacity even at the highest load employed, they promote the formation of iron-rich transfer layer and they also delay the fracture of Saffil short fibres to higher loads. Under the experimental conditions used in the present investigation, the dominant wear mechanism is found to be abrasion for the AE42 alloy and its composites. It is accompanied by severe plastic deformation of surface layers in case of alloy and by the fracture of Saffil short fibres as well as the formation of iron-rich transfer layer in case of composites.

An investigation on corrosion behaviour of pressure infiltrated Al–Mg alloy/SiC p composites

In this study, effect of Mg alloying addition (2–8 wt.%) on corrosion behaviour of Al matrix composites, in 3.5 wt.% NaCl environment, has been investigated. Composites were produced by pressure infiltration technique at 750 °C and had a SiC particle (SiC p) volume fraction of ∼60%. Results were evaluated by using potentiodynamic polarisation measurements, immersion tests, SEM, EDS and XRD analysis. Compared to the pure Al matrix, mass loss of the composites decreased with increasing Mg content. Experimental results revealed that intermetallics as a result of reaction between Al–Mg alloy and SiC particle has beneficial effect on corrosion resistance of the composites due to interruption of the continuity of the matrix channels within the pressure infiltrated composites.

Multi-functional SiC/Al Composites for Aerospace Applications

Multi-functional Al-matrix composites with high volume fraction (55%-57%) of SiC particles are produced with the new pres-sureless infiltration fabrication technology. X-ray detection and microscopic observation display the composites which are macroscopi-cally homogeneous without porosity. The investigation further reveals that the SiC/Al composites possess low density (2.94 g/cm3), high elastic modulus (220 GPa), prominent thermal management function as a result of low coefficient of thermal expansion (8×10−6 K−1) and high thermal conductivity (235 W/(m·K)) as well as unique preventability of resonance vibration. By adopting a series of developed techniques, the multi-functional SiC/Al composites have managed to be made into near-net-shape parts. Many kinds of precision components of space-based optomechanical structures and airborne optoelectronic platform have been turned out. Of them, several typical products are being under test in practices.

Fabrication of SiC particle dispersed spheroidal graphite cast iron composite by vacuum assisted casting and its microstructure

SiC particle preforms were infiltrated with spheroidal graphite cast iron melt by vacuum assisted casting in the sand mould, and spheroidal graphite cast iron composites in which the particles were dispersed in the surface region were fabricated. Although the melt infiltration was not accomplished when the melt was poured under atmospheric pressure, the infiltration was accomplished by the vacuum assisted casting when the SiC particle volume fraction and preform thickness were optimised. When the Si content of the cast iron was 2˙5 mass%, the phase consisting of mainly Fe3Si was formed at the particle/matrix interface due to the reaction between the cast iron melt and the particles during the infiltration. The matrix of the composite consisted of fine spheroidal graphite particles, ferrite, pearite and chill crystal. Although the increase in the Si content suppressed the reaction and chill, no infiltrated area was observed in the composite.

Study of SiCp/AZ61 Composites

SiCp/AZ61 composites were fabricated by a semi-solid stirring method. The effects of volume fraction of SiC particles, stirring temperature and stirring time on the mechanical properties of SiCp/AZ61composites were studied with an orthogonal experimental method. The results indicate that volume fraction of SiC particles has a remarkable influence on the mechanical properties of SiCp/AZ61 composites, the second were stirring time and stirring temperature. In this experiment condition, the optimum technological parameters of SiCp/AZ61 composites fabricated by semi-solid stirring method were volume fraction of SiC particles 6%, stirring temperature 595°C and stirring time 5 min. Fractographies show that the fracture morphology of SiCp/AZ61 composites with volume fraction of SiC particles 6% is brittle.

Incorporation of new technique for processing of Al/SiCp composites based on evaporative pattern casting (EPC) method

A336 Al matrix composites containing different volume fraction and mean mass particle size of SiC particles as the reinforcing phase were synthesised by evaporative pattern casting (EPC) route. The process consisted of fabricating of EPS/SiCp composite pattern followed by EPC of A336 Al alloy. The EPS/SiCp pattern was made by blending SiC particles with expandable polystyrene (EPS) beads and placing them in expanding mould heating with steam until EPS beads expand completely. Uniform distributed SiC particles around the EPS beads and locally movement of them during pouring and degradation leads to homogenous distribution of particles in final Al/SiCp composite. Higher modulus, strength and hardness were observed in the composites than the unreinforced Al alloy part. The fracture surfaces of the composite samples exhibited dimple surfaces and fracture in SiC particles.

Effects of strain rate and SiC particle on the compressive property of SiC p/AlSi 9Mg composite foams

The AlSi 9Mg composite foams reinforced by SiC particles (SiC p/AlSi 9Mg composite foams) were fabricated with the direct foaming route of melt using CaCO 3 blowing agent. The static and dynamic compressive behaviors of the composite foams were investigated utilizing CMT5205 electron universal testing machine and a Split Hopkinson Pressure Bar system, respectively. The experimental results show that the yield stress of SiC p/AlSi 9Mg composite foams increases with increasing strain rate, the strain hardening occurs during the compression at high strain rate, and SiC p/AlSi 9Mg composite foams is more sensitive to the strain rate than Al and Al alloy foams. The yield stress of SiC p/AlSi 9Mg composite foams with different volume fractions of SiC particles at high strain rate increases with the increase of the volume fraction of SiC particles.

Research on Properties of SiCp/AZ61 Magnesium Matrix Composites in Fabrication Processes

The microstructural structures of SiCp/AZ61magnesium matrix composite were studied in three different casting processes, and their hardness was measured. The results indicated that SiCp/AZ61 composites fabricated in stirring melt casting process, compared to those in fully liquid stirring casting process and in semi-solid stirring casting process, possessed fairly uniform distribution of SiC particulates and few porosity rate. It was an ideal metal matrix composites fabricated process. The Vickers hardness of non-reinforcement AZ61 magnesium alloy is higher than that of semi-solid billet, and the Vickers hardness of SiCp/AZ61 composite is obviously higher than that of the matrix. In the meantime, the Vickers hardness of SiCp/AZ61 composite can be continuously enhanced with an increasing of volume fraction of SiC particles.

Surface Nano-Deformation Behavior in Particle-Reinforced Al Composite

The surface nano-deformation behavior in metal matrix composite during tensile loading was investigated by in-situ atomic force microscope (AFM) observation. The composite material used was aluminum matrix reinforced with 10 and 20 percent volume fraction of SiC particles. The average size of the reinforcement was 3 μm. Tensile test and in-situ observations were conducted using a loading device equipped with an AFM. Surface morphologies of the composite specimens were acquired before the loading and at various stages of the loading. The microstructural damage and the evolution of surface roughness were studied. The effect of volume fraction of the reinforcement on the nano-deformation behavior and damage evolution process of the composite based on nanoscale in-situ AFM observation will be discussed.

Thermal conductivity of Al–SiC composites with monomodal and bimodal particle size distribution

The thermal conductivity of aluminum matrix composites having a high volume fraction of SiC particles is investigated by comparing data for composites fabricated by infiltrating liquid aluminum into preforms made either from a single particle size, or by mixing and packing SiC particles of two largely different average sizes (170 and 16 μm). For composites based on powders with a monomodal size distribution, the thermal conductivity increases steadily from 151 W/m K for particles of average diameter 8 μm to 216 W/m K for 170 μm particles. For the bimodal particle mixtures the thermal conductivity increases with increasing volume fraction of coarse particles and reaches a roughly constant value of 220 W/m K for mixtures with 40 or more vol.% of coarse particles. It is shown that all present data can be accounted for by the differential effective medium (DEM) scheme taking into account a finite interfacial thermal resistance.

A nanoindentation analysis of the effects of microstructure on elastic properties of Al 2O 3/SiC composites

Nanoindentation tests were carried out to investigate certain elastic properties of Al 2O 3/SiC p composites at microscopic scales (nm up to μm) and under ultra-low loads from 3 mN to 250 mN, with special attention paid to effects caused by SiC particles and pores. The measured Young’s modulus depends on the volume fraction of SiC particles and on the composite porosity and it can compare with that of alumina. The Young’s modulus exhibits large scatters at small penetrations, but it tends to be constant with lesser dispersion as the indentation depth increases. Further analysis indicated that the scatter results from specific microstructural heterogeneities. The measured Young’s moduli are in agreement with predictions, provided the actual role of the microstructure is taken into account.

Compression Creep Behavior of High Volume Fraction of SiC Particles Reinforced Al Composite Fabricated by Pressureless Infiltration

The compression creep deformation of the high volume fraction of SiC particles reinforced Al-Mg-Si composite fabricated by pressure-less infiltration was investigated. The experimental results show that the creep stress exponents are very high at temperatures of 673 K, 723 K and 773 K, and if taking the threshold stress into account, the true stress exponent of minimum creep strain rate is still approximately 5, although the volume fraction of reinforcements is very high. The creep strain rate in the high volume fraction reinforced aluminum alloy matrix composites is controlled by matrix lattice diffusion. It is found that the creep-strengthening effect of high volume fraction of silicon carbide particles is significant, although the particles do not form effective obstacles to dislocation motion.

Structure and Wear Properties of Sic Reinforced Al-Li (8090) Alloy in the Cast and Heat Treated Conditions

Different percentages of SiC particulates (0-15 wt%) were introduced into Al-Li (8090) to produce composite by using the vortex technique. Microstructural studies of both Al-Li and Al-Li composites were carried out in the cast and heat treated conditions. The results showed that the cast composite obtained some degree of porosity especially with a high volume fraction (15% of SiC) particulates. The examination of SiC reinforced alloys in the cast and heat treated conditions showed an increasing grain refining effect compared to the Al-Li base alloy. As the volume fraction of SiC particulates increased from 5 to 15% the hardness also increased from 68 to 108 HB in the cast condition and from 90 to 120 HB in the peak aged condition. This increase in hardness was related to the modified structure and the hard dispersed SiC particulates. Mechanical deformation of 50% reduction in thickness by rolling was applied to the investigated alloys to study its effect on impact strength and wear properties. Dry sliding wear test was performed on both cast and peak aged conditions. The deformed alloys showed better wear results than the cast ones due to the strain hardening occurred during the rolling process. The minimum wear rate was obtained at 10% SiC in both cast and heat treated conditions.