An investigation of the effect of SiC particle size on Cu–SiC composites

In this study mechanical properties of copper were enhanced by adding 1 wt.%, 2 wt.%, 3 wt.% and 5 wt.% SiC particles into the matrix. SiC particles of having 1 μm, 5 μm and 30 μm sizes were used as reinforcement. Composite samples were produced by powder metallurgy method and sintering was performed in an open atmospheric furnace at 700 °C for 2 h. Optical and SEM studies showed that the distribution of the reinforced particle was uniform. XRD analysis indicated that the dominant components in the sintered composites were Cu and SiC. Relative density and electrical conductivity of the composites decreased with increasing the amount of SiC and increased with increasing SiC particle size. Hardness of the composites increased with both amount and the particle size of SiC particles. A maximum relative density of 98% and electrical conductivity of 96% IACS were obtained for Cu–1 wt.% SiC with 30 μm particle size.     

Grey correlation analysis between strength of slag cement and particle fractions of slag powder

The particle size distributions of slag powder were investigated by Laser Scatter equipment. The influence of particle fractions of slag powder on the compressive strength of slag cement composed of 50% slag powder and 50% Portland cement was also studied by the method of grey correlation analysis. The results indicated that the volume fraction of particles 5–10 μm had a maximum positive effect on the mortar compressive strength of slag cement at 7 d and the volume fraction of particles 10–20 μm had a maximum positive effect on the mortar compressive strength at 28 d, whereas the volume fraction of particles larger than 20 μm had a negative effect on the mortar compressive strength at 7 and 28 d.     

Characterization of centrifugal cast functionally graded aluminum-silicon carbide metal matrix composites

The present investigation is on characterization of functionally graded composites based on 356 cast and 2124 wrought aluminum alloys reinforced with SiC particles of 23 μm average particle size processed by liquid metal stir casting followed by horizontal centrifugal casting. A maximum of 45 and 40% SiC particles are obtained at the outer periphery of the Al(356)-SiC and Al(2124)-SiC FGMMC casting respectively. The maximum hardness obtained at the outer periphery after heat treatment for Al(356)-SiC and Al(2124)-SiC FGMMC are 155 BHN and 145 BHN respectively. The freezing range of the matrix alloy has been found to dictate the nature of transition from particle enriched to depleted zone. These composites are suitable for making engineering components, which require very high surface hardness and wear resistances with high specific strength.     

Structure and strength of aluminum with sub-micrometer/micrometer grain size prepared by spark plasma sintering

A spark plasma sintering (SPS) technique has been applied to prepare fully dense Al samples from Al powder. By applying a sintering temperature of 600 °C and a loading pressure of 50 MPa, fully recrystallized samples of nearly 100% density with average grain sizes of 5.2 μm, 1.3 μm and 0.8 μm have been successfully prepared using a sintering time of less than 30 min and without the need for a nitrogen atmosphere. A similarity between the grain size and powder particle size is found, which suggests a potential application of the SPS technique to prepare samples with a variety of grain sizes by tailoring the initial powder particle size. The SPS samples show higher strength than Al samples with an identical grain size prepared using thermo-mechanical processing, and a better strength–ductility combination, with the 1.3 μm grain size sample showing a yield strength (σ_0.2%) of 140 MPa and a uniform elongation of more than 10%. This higher strength is related to the presence of oxide particles in the grain boundaries of the samples. It is concluded that SPS is an excellent technique for the production of very fine grained Al materials with high strength, by combining both grain boundary and oxide dispersion strengthening.     

Utilization of natural zeolite in aerated concrete production

In this study, natural zeolite (clinoptilolite) was used as an aggregate and bubble-generating agent in autoclaved aerated concrete (AAC) production. The crushed and grinded samples were classified into two different particle sizes: 100 μm (fine-ZF) and 0.5–1 mm (coarse-ZC) before using in AAC mixtures. The effects of particle size, replacement amount (25%, 50%, 75% and 100% against quartz) and curing time on the AAC properties were experimentally investigated. It was found that usage of natural zeolite, especially with a coarser particle size, has beneficial effect on the physical and mechanical properties of AAC. The optimum replacement amount was determined as 50% and at this rate the compressive strength, unit weight and thermal conductivity of AAC were measured as 3.25 MPa, 0.553 kg/dm³ and 0.1913 W/mK, respectively. Scanning electron microscopy analysis also confirmed the above findings. Denser C–S–H structures were obtained up to a replacement amount of 50%. Finally, the test results demonstrated that calcined zeolite acts as both an aggregate and a bubble-generating agent, and that AAC with a compressive strength of 4.6 MPa and unit weight of 0.930 kg/dm³ can be produced without aluminum powder usage.     

Analysis of the compaction behavior of Al–SiC nanocomposites using linear and non-linear compaction equations

The compressibility behavior of Al–SiC nanocomposite powders was examined and the density-pressure data were analyzed by linear and non-linear compaction equations. SiC particles with an average size of 50 nm were mixed with gas-atomized aluminum powder (40 μm average size) at different volume fractions (up to 20 vol%) and compacted in a rigid die at various pressures. In order to highlight the effect of reinforcement particle size, the compressibility of micrometric SiC particles of two sizes (1 and 40 μm) was also examined. Analysis of the compressibility data indicated hindering effect of the hard ceramic particles on the plastic deformability of soft aluminum matrix, particularly at high volume fractions. More pronounced effect on the yield pressure was obtained for the nanometric particles compared with the micrometric ones. Nevertheless, better particles rearrangement was taken place when the ultrafine SiC particles were utilized. In light of the experimental and theoretical analysis, the densification mechanism of aluminum matrix composites and the effect of reinforcement particle size and volume fraction are discussed.     

Growth of SiC particles in reaction sintered SiC

For reaction sintered SiC (RSSC) prepared at 1600°C by conventional melt infiltration technique, experimentation with two different particle sizes of initial SiC, viz., 0.2 and 23.65 μm, showed that the large SiC particles remained unaltered and the sizes of the fine-grained SiC increased several times yielding well-developed faceted crystals in the final material. To study the process further, compacts of SiC powder of particle sizes varying between 0.20 and 8.99 μm were reacted with pure Si at 1600°C and the resulting SiC–Si boundaries were studied by optical microscopy. A distinct boundary layer with no penetration of Si in the compact of SiC of 0.2 μm was observed and the width of the SiC–Si boundary was found to be increasing linearly with time. Detailed SEM examination establishes the growth of the SiC upto around 4 μm from 0.2 μm starting powder. No such growth was observed in the case of starting SiC powder coarser than 0.2 μm. The growth of SiC is explained in terms of solution-reprecipitation mechanism.     

Refining SiCp in reinforced Al–SiC composites using equal-channel angular pressing

Aluminum–silicon carbide composite (Al–SiC_p) is one of the most promising metal matrix composites for their enhanced mechanical properties and wear resistance. In the present study, Al–SiC (average size 55 μm) composites with 5% and 10% by volume were fabricated by stir casting technique. The equal-channel angular pressing (ECAP) was then applied on the cast composites at room temperature in order to study the effect of ECAP passes on the SiC_p size and distribution. The ECAP process was successfully carried out up to 12(8) passes for Al–5%(10%)SiC samples. Microstructure study revealed that the highest refinement by breakage of SiC_p was achieved after the first ECAP pass and that further refinement took place in the next passes. More breakage of the SiC_p was found in the composite richer in reinforcing particles so that the SiC_p reached approximately 1 μm in the Al–10%SiC after 8 passes and 4 μm in Al–5%SiC after 12 ECAP passes. The distribution of SiC reinforcement particles also improved after applying ECAP. The factors including decrease in reinforcing particle size, improvement in their distribution, decrease in porosity in addition to strain hardening and grain refining of the matrix resulted in enhancement of tensile and compressive strengths as well as hardness by more than threefold for the Al–5%SiC after 12 passes and for Al–10%SiC after 8 passes compared to the cast composites. Additionally, the composite remained ductile after the ECAP process. The fracture surface indicated good bond between the matrix and the reinforcement.     

Mechanical properties of a diamond–copper composite with high thermal conductivity

Using pressureless infiltration of copper into a bed of coarse (180 μm) diamond particles pre-coated with tungsten, a composite with a thermal conductivity of 720 W/(m K) was prepared. The bending strength and compression strength of the composite were measured as 380 MPa. As measured by sound velocity, the Young's modulus of the composite was 310 GPa. Model calculations of the thermal conductivity, the strength and elastic constants of the copper–diamond composite were carried out, depending on the size and volume fraction of filler particles. The coincidence of the values of bending strength and compressive strength and the relatively high deformation at failure (a few percent) characterize the fabricated diamond–copper composite as ductile. The properties of the composite are compared to the known analogues — metal matrix composites with a high thermal conductivity having a high content of filler particles (~ 60 vol.%). In strength and ductility our composite is superior to diamond–metal composites with a coarse filler; in thermal conductivity it surpasses composites of SiC–Al, W–Cu and WC–Cu, and dispersion-strengthened copper.     

Processing of Al/SiC composites in continuous solid–liquid co-existent state by SPS and their thermal properties

Silicon carbide (SiC)-particle-dispersed-aluminum (Al) matrix composites were fabricated in a unique fabrication method, where the powder mixture of SiC, pure Al and Al–5mass% Si alloy was uniquely designed to form continuous solid–liquid co-existent state during spark plasma sintering (SPS) process. Composites fabricated in such a way can be well consolidated by heating during SPS processing in a temperature range between 798 K and 876 K for a heating duration of 1.56 ks. Microstructures of the composites thus fabricated were examined by scanning electron microscopy and no reaction was detected at the interface between the SiC particle and the Al matrix. The relative packing density of the Al–matrix composite containing SiC was higher than 99% in a volume fraction range of SiC between 40% and 55%. Thermal conductivity of the composite increased with increasing the SiC content in the composite at a SiC fraction range between 40 vol.% and 50 vol.%. The highest thermal conductivity was obtained for Al–50 vol.% SiC composite and reached 252 W/mK. The coefficient of thermal expansion of the composites falls in the upper line of Kerner’s model, indicating strong bonding between the SiC particle and the Al matrix in the composite.     

Investigating effects of process parameters on microstructural and mechanical properties of Al5052/SiC metal matrix composite fabricated via friction stir processing

Friction stir processing (FSP) is a novel process for refinement of microstructure, improvement of material’s mechanical properties and production of surface layer composites. In this investigation via friction stir processing, metal matrix composite (MMC) was fabricated on surface of 5052 aluminum sheets by means of 5 μm and 50 nm SiC particles. Influence of tool rotational speed, traverse speed, number of FSP passes, shift of rotational direction between passes and particle size was studied on distribution of SiC particles in metal matrix, microstructure, microhardness and wear properties of specimens. Optimum of tool rotational and traverse speed for achieving desired powder dispersion in MMC was found. Results show that change of tool rotational direction between FSP passes, increase in number of passes and decrease of SiC particles size enhance hardness and wear properties.     

Explosive consolidation of 316L stainless steel powder – Effect of phase composition

Two stainless steel (SS) AISI 316L powders have been processed by explosive consolidation using a cylindrical configuration. Powders with d₅₀ of 9 and 5 μm and a phasic structure consisting of fcc and bcc are used. After shock processing (3.5 up to 4.9 mm/μs) hardness was evaluated. Powders with the lowest particle size and processed with the highest detonation velocities (4.9 and 4.1 mm/μs) gave rise to a bulk material where in the centre occurred a phase transformation of bcc to fcc phase. Nevertheless, the hardness values were dissimilar along the cross section depending on the macrodefects (centre hole and cracks) produced by detonation. After a pre-heating treatment (900 °C), this powder was full austenitic (fcc) and when submitted to explosive consolidation, it led a monolithic solid without cracks, with a density of 99% TMD (theoretical maximum density) and a hardness of 3.1 GPa. This value is lower than others measured, particularly when a centre hole is not present, revealing hardening by plastic deformation. Concerning powder with higher particle size (d₅₀ = 9 μm), the presence of mainly austenite induces after shock processing function of detonation parameters and localisation hardness values from 3.9 up to 5.0 GPa. The homogeneity of hardness reflex of absence of defects and low stress are almost achieved only for low particle size powders, using the lowest detonation velocities (3.4 GPa).     

Mechanical properties of rolled A356 based composites reinforced by Cu-coated bimodal ceramic particles

Three kinds of A356 based composites reinforced with 3 wt.% Al₂O₃ (average particle size: 170 μm), 3 wt.% SiC (average particle size: 15 μm), and 3 wt.% of mixed Al₂O₃–SiC powders (a novel composite with equal weights of reinforcement) were fabricated in this study via a two-step approach. This first process step was semi-solid stir casting, which was followed by rolling as the second process step. Electroless deposition of a copper coating onto the reinforcement was used to improve the wettability of the ceramic particles by the molten A356 alloy. From microstructural characterization, it was found that coarse alumina particles were most effective as obstacles for grain growth during solidification. The rolling process broke the otherwise present fine silicon platelets, which were mostly present around the Al₂O₃ particles. The rolling process was also found to cause fracture of silicon particles, improve the distribution of fine SiC particles, and eliminate porosity remaining after the first casting process step. Examination of the mechanical properties of the obtained composites revealed that samples which contained a bimodal ceramic reinforecment of fine SiC and coarse Al₂O₃ particles had the highest strength and hardness.     

Influence of different particle sizes on reactivity of finely ground glass as supplementary cementitious material (SCM)

Finely ground glass can be pozzolanically reactive and serve as a supplementary cementitious material (SCM). In this study, the pozzolanic reactivity of three narrow size ranges of green glass cullet, 63–75 μm, 25–38 μm, and 0–25 μm was investigated in order to understand the effects of particle size on glassy SCM reactivity. Isothermal calorimetry, chemical shrinkage, thermogravimetric analysis, and leaching tests were used to measure cement and glass dissolution and reactions. Images taken by scanning electronic microscope (SEM) in backscattered (BS) mode were analyzed to measure glass degree of hydration. In addition, mortar compressive strength and water absorption of samples containing glass powder at different curing temperatures and ages were used to relate reaction degree to performance. Results showed that hydration degree of the glass particles could be directly accounted for through linear correlation with particles surface area.     

Morphology and thermal conductivity of polyacrylate composites containing aluminum/multi-walled carbon nanotubes

Polyacrylate composites with various fillers such as multi-walled carbon nanotube (CNT), aluminum flake (Al-flake), aluminum powders and Al–CNT were prepared by a ball milling. The thermal decomposition temperature increased by as much as 64 °C for polyacrylate/Al-flake 70 wt% composite compared to polyacrylate. The thermal conductivity of polyacrylate/Al–CNT composites increased from 0.50 to 1.67 W/m K as the Al–CNT content increases from 50 to 80 wt%. The thermal conductivity of the composite sheet increases with the sheet thickness. At the given filler concentration (90 wt%), the composite filled with aluminum powder of 13 μm has a higher thermal conductivity than the one filled 3 μm powder, and the composite filled with mixture of two powders showed a synergistic effect on the thermal conductivity. The morphology indicates that the dispersion of CNT in the polyacrylate/Al-flake + CNT composite is not perfect, and agglomeration of CNTs was observed.     

Effects of copper addition on the in-situ synthesis of SiC particles in Al–Si–C–Cu system

In this research work, SiC particles have been successfully in-situ synthesized in Al–Si–Cu matrix alloy utilizing a novel liquid–solid reaction method. The effect of copper addition on the synthesis of SiC in Al–Si–C–Cu system was investigated. The composites mainly contain spherical SiC particles and θ-Al₂Cu eutectic phases, which are embedded in the α-Al matrix. Results indicated that the temperature for forming in-situ SiC particles significantly reduced from 750 °C to 700 °C with the copper addition. The size of in-situ synthesized SiC particles can be as low as 0.2 μm. Further study found that the addition of 10 wt.% copper into Al–Si–C alloy causes its solidus temperature to decrease by about 65 °C. Additionally, the Rockwell hardness value of SiCp/Al–18Si–5Cu composites has an average of 92, which is 50% higher than that of the sample without copper addition.     

Investigation of impact behaviour of aluminium based SiC particle reinforced metal–matrix composites

In this paper, the impact behaviour of aluminium and silicon carbide (SiC) particle reinforced aluminium matrix composites under different temperature conditions was determined. Charpy impact tests were performed on as extruded and heat treated specimen at temperatures varying from −176 to 300 °C. Composite specimens based on aluminium alloys of 2124, 5083 and 6063 and reinforced by SiC particles were manufactured. Two different SiC sizes of 157 μm and 511 μm and two different extrusion ratios of 13.63:1 and 19.63:1 were used. The results of instrumented impact tests were compared with the microstructural and fractographic observations. The failure mechanisms and deformation behaviour of unreinforced alloys and composites were assessed. The impact behaviour of composites was affected by clustering of particles, particle cracking and weak matrix-reinforcement bonding. Agglomeration of particles reduced the impact strength of Al 2124 and 6063 based composites. Alumınum 6063 alloys and composites showed a better impact strength. The impact strength of 6063 composites increased with particle size and extrusion ratio. The effects of the test temperature on the impact behaviour of all materials were not very significant.     

Thermal conductivity of Cu/diamond composites prepared by a new pretreatment of diamond powder

Cu/diamond composites were fabricated by spark plasma sintering (SPS) after the surface pretreatment of the diamond powders, in which the diamond particles were mixed with copper powder and tungsten powder (carbide forming element W). The effects of the pretreatment temperature and the diamond particle size on the thermal conductivity of diamond/copper composites were investigated. It was found that when 300 μm diamond particles and Cu–5 wt.% W were mixed and preheated at 1313 K, the composites has a relatively higher density and its thermal conductivity approaches 672 W (m K)⁻¹.     

Influence of carbon precursors on thermal plasma assisted synthesis of SiC nanoparticles

Nanosized SiC was synthesized by solid state method using silicon and carbon powders followed by non-transferred arc thermal plasma processing. X-ray diffraction (XRD) analysis revealed that activated carbon has highest reactivity while graphite has lowest activity in the crystallization of SiC through solid state method. The reactivity was dependent on surface area of carbon source and activated carbon with highest surface area (590.18 m² g⁻¹) showed highest reactivity, whereas graphite with least surface area (15.69 m² g⁻¹) showed lowest reactivity. The free silicon content was decreased with increasing reaction time as well as carbon mole ratio. Scanning electron microscope (SEM) study showed that the shape and size of synthesized SiC depends on the shape and size of carbon source. SiC nanoparticles within 500 nm were formed for carbon black while bigger particles (∼5 μm) were formed for activated carbon and graphite. Plasma processing of these solid–solid synthesized SiC resulted into the formation of well dispersed, ultrafine SiC nanoparticles (30–40 nm) without any structural modification. Thermal plasma processing resulted into the increase in crystallite size of SiC.     

Aluminum matrix composites based on preceramic-polymer-bonded SiC preforms

Polymethylsiloxane (PMS) was used as a binder to make self-supporting SiC preforms for pressurized aluminum melt infiltration. The SiC particles were coated with preceramic polymer by spray drying; this ensured a fine and homogeneous distribution coupled with a high yield of the binder. The conditioned SiC powder mixtures were processed into preforms by warm pressing, curing and pyrolysis. A polymer content of 1.25 wt.% conferred sufficient stability to the preforms to enable composite processing. Using this procedure, SiC preforms with various SiC particle size distributions were prepared. The resulting Al/SiC composites with SiC contents of about 60 vol.% obtained by squeeze casting infiltration exhibit a 4-point bending strength of ∼500 MPa and Young’s moduli of ∼200 GPa. These values are comparable to those of compositionally identical, but binder-free composites. It is thus shown that the PMS-derived binder confers the desired strength to the SiC preforms without impairing the mechanical properties of the resulting Al/SiC composites.