Dispersion Of SiC Particles Research Articles

Role of the Initial Degree of Ionization of Polyethylenimine in the Dispersion of Silicon Carbide Nanoparticles

The role of the initial degree of ionization (αi) of polyethylenimine (PEI) in the dispersion of SiC nanopartilces in water was investigated by sedimentation and rheological measurements. The ionization of PEI was characterized by potentiometric titration, which indicated a pH‐dependent conformational transition. The dispersion of SiC particles in the presence of PEI was found to strongly depend on the αi. In the presence of 0.4% by weight PEI, the 23.8% SiC by volume (ΦSiC= 23.8) slurries showed a Newtonian behavior for αi= 0.12–0.4 values, whereas a shear‐thinning behavior was observed for αi > 0.4 in the optimal pH range of around pH 4. The rheological behavior of the slurries exhibited a strong dependence on the concentration of PEI of αi= 0.12–0.4 and the slurry showed a Newtonian behavior at an optimal concentration of 0.4% by weight. The stabilization may be dominated by an electrosteric effect arising from the adsorbed PEI of αi= 0.12–0.4. The flocculation mechanism of the slurries with PEI of αi > 0.4 is also discussed.

Mechanical properties and microstructure for 3 mol% yttria doped zirconia/silicon carbide nanocomposites

Abstract 3 Mol% yttria stabilized tetragonal zirconia polycrystalline (3Y-TZP) is well known as a transformation toughening material with excellent mechanical properties at ambient temperature. However, the properties of 3Y-TZP drop down with increasing temperature. In this study, nanocomposite techniques were applied in order to improve mechanical properties of 3Y-TZP. 3Y-TZP/SiC nanocomposites were fabricated by hot-pressing, and effects of SiC particles on microstructure, transformation from tetragonal zirconia (t-ZrO 2 ) to monoclinic ZrO 2 (m-ZrO 2 ) and its mechanical properties were investigated. Fracture toughness of the nanocomposite was improved without decrease of strength. This should be due to not only crack deflection by dispersed SiC particles with high Young's modulus, but also the phase transformation of t-ZrO 2 accelerated by the residual stresses from coefficient of thermal expansion mismatch between 3Y-TZP and SiC.

Pretreatment process of SiC particles and fabrication technology of SiC particulate reinforced Zn–Al alloy matrix composite

In the present paper, a novel pretreatment process for SiC particulate and a new mechanical–electromagnetic combination stirring process for fabricating Zn–Al(ZA27)/SiCp composites are described. The optimal pretreatment route and the most appropriate SiC particle parameters were experimentally determined. The pretreated SiC particles were easily incorporated and dispersed in the ZA27 alloy melt and were not agglomerated before addition to the melt. The surface status of the SiC particles before and after pretreatment was observed and analysed by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and transmission electron microscopy. It was found that gas existing on the SiC particle surfaces by physical and chemical absorption was a significant hindrance to the incorporation and dispersion of SiC particles in the alloy melt. The gas absorption was induced by ultrafine SiC powders, fracture steps, and ions existing on the SiC particle surfaces. The carbon, silicon, and oxygen contents on the SiC surface were varied with different pretreatment techniques. Moreover, a dense layer of amorphous SiO2, which improves wetting of SiC particles in the ZA27 melt, was formed owing to calcination of SiC particles in air. The new combined stirring process exploits the advantages of both mechanical and electromagnetic stirring of the melt at the different processing stages during fabrication. The microstructural characteristics of the resulting composites are: homogeneously distributed SiC particles, fewer macro gas blows and inclusions, and little shrinkage porosity in comparison to composites fabricated by a mechanical stirring process. Finally, the mechanisms of degassing and reducing the porosity and the number of oxide inclusions are discussed.

Elastic Constant Determinations of SiC/NiP Composite Coating by Surface Acoustic Wave and Nano-indentation

Elastic constant determinations of coatings deposited on a substrate are performed using a surface acoustic wave technique, and the ultrasonically determined elastic constants are compared with mechanically determined ones using a nano-indentation technique in order to examine the present ultrasonic technique for its validity. The experimental results for a NiP coating have shown that the Young's moduli determined ultrasonically and mechanically coincide with each other within an error range of 2%. This demonstrates that the present ultrasonic technique has been successfully applied to the elastic constant determination of such coating. Based on this result, SiC/NiP composite coating (SiC particle reinforced NiP coating) of 10 µm thickness was examined. The result using the surface acoustic wave indicated a 32% increase in Young's modulus due to the randomly dispersed SiC particles. The validity of this result is also discussed in comparison with mechanically and theoretically estimated results.

324 無電解NiPメッキの力学特性におよぼす熱処理および粒子分散の影響(OS 薄膜特性)

Elastic property determinations of several kinds of electroless Ni-P coatings deposited on a steel substrate have been performed. First, Young's moduli of NiP composite coatings are determined using a surface acoustic wave spectroscopy and the ultrasonically determined ones are compared with both mechanically determined ones using a nanoindentation and theoretically estimated ones. The results have clearly shown that SiC particles dispersion causes an increase in Young's modulus of composite coatings and conversely, Teflon particles dispersion decreases Young's modulus. Next, Young's moduli for several NiP coatings heat-treated at various temperature are examined. The result has shown that Young's modulus of NiP coating increases up to about 33% as tempering temperature increases and it has a maximum value by heat-treating at 773K.

Influence of processing parameters during disintegrated melt deposition processing on near net shape synthesis of aluminium based metal matrix composites

This paper addresses the influence of processing parameters on the near net shape synthesis of Al–SiC particle reinforced metal matrix composites by the disintegrated melt deposition technique. The processing parameters that were investigated include stirring speed during reinforcement addition, holding and stirring times following reinforcement addition, and total flight distance. The effect of the weight fraction of SiC incorporated was also studied. Maximum incorporation of the reinforcement was achieved by dispersing SiC particles in liquid aluminium with an impeller at a stirring speed of 500 rev min-1. Composite porosity levels were minimised for holding and stirring times following SiC addition of 15 and 5 min, respectively, and for a total flight distance of 450 mm. Composite porosity levels were increased with increasing weight fractions of SiC incorporated. The results obtained clearly demonstrate the dependence of composite porosity levels on weight fraction of reinforcement incorporated, total flight distance, and holding and stirring times following addition of SiC particles, and reinforcement incorporation on stirring speed.

Sliding wear response of a zinc-aluminum alloy as affected by SIC particle dispersion and test conditions

Sliding wear response of a zinc-aluminum alloy as affected by SIC particle dispersion and test conditions

Preparation and thermal stability of ceramic/metallic glass composites prepared by mechanical alloying

We present the formation of ceramic/metallic glass composite powders by mechanical alloying of an elemental powder mixture with the composition Zr 65Al 7.5Ni 10Cu 17.5 together with SiC particles. The effect of the added ceramic particles on glass formation and thermal stability was investigated with structural and thermal analysis. During the milling process an amorphous matrix with a homogeneous dispersion of SiC particles develops. This composite material reveals a distinct glass transition followed by crystallization. The onset temperatures for these transformations are found to be increased by about 10 K in comparison to the amorphous Zr-based alloy without SiC. This observation may be explained by small compositional changes in the amorphous matrix during the milling process. No indication for SiC dispersoids acting as heterogeneous nucleation sites was found. The kinetics of primary crystallization was found to be delayed. The microhardness of the ceramic/metallic glass composites was increased by about 25% compared to the value found for the single amorphous powder. As such, mechanical alloying represents a useful method for the preparation of ceramic/metallic glass composite powders combining the mechanical properties of the amorphous state and the ceramic particle dispersions.

In Situ Processing and Properties of SiC/MoSi2 Nanocomposites

A novel concept for in situ processing of SiC/MoSi2 nanocomposites has been developed that combines the pyrolysis of MoSi2 particles coated with polycarbosilane and subsequent densification by hot pressing. After densification, a uniform dispersion of SiC particles is obtained in the MoSi2 matrix. The strength at both room and elevated temperature is dramatically improved by the processing protocol employed. The average room‐temperature flexural strength measured for the SiC/MoSi2 nanocomposite was 760 versus 150 MPa for unreinforced MoSi2. The average 1250°C flexural strength measured for the SiC/MoSi2 nanocomposite was 606 versus 77 MPa for unreinforced MoSi2.

Formation of Ceramic/Metallic Glass Composite by Mechanical Alloying

Recently discovered Zr-based bulk glass alloys can be produced by rapid quenching from the melt or as an alternative route by mechanical alloying. Here we present the formation of amorphous matrix-ceramic composite powders by mechanical alloying of an elemental powder mixture with the composition Zr 65 Al 7.5 Ni 10 Cu 17.5 together with SiC particles. The effect of the added ceramic particles on glass formation and thermal stability was investigated with structural and thermal analysis. During the milling process an amorphous matrix with a homogeneous dispersion of SiC particles develops. This composite material reveals a glass transition followed by crystallization. The onset temperatures for these transformations are found to be increased by about 10 K in comparison the pure Zr-based alloy. This observation may be explained by small compositional changes in the amorphous matrix during the milling process. No indication for SiC dispersoids acting as heterogeneous nucleation sites was found. The kinetics of primary crystallization was found to be delayed. As such, mechanical alloying represents a useful method for preparation of amorphous-ceramic powders combining the improved mechanical properties of the amorphous state and particle dispersions.

Pressureless sintering and elastic constants of Al 2O 3-SiC ‘nanocomposites’

A study is presented of how to obtain very near theoretical densities (≥99.6%) in Al 2O 3-SiC ‘nanocomposites’ by pressureless sintering. Several factors are considered in order to achieve the optimal densification. The most important factors are: good dispersion of SiC particles in the matrix, cold-isostatic pressing of green samples and use of a relatively coarse-sized bedding powder (which allows efficient effusion of carbon monoxide from the sample), correct choice of sintering temperature (which depends on the size of alumina particles), and the use of a nitrogen atmosphere during sintering. The elastic constants of the nanocomposites produced depend on the degree of densification. About 2% reduction from theoretical density leads to about a 6% reduction of the Young's modulus. The experimentally obtained moduli are correlated with three models that relate porosity to Young's modulus.

Influence of SiC Particle Size on Creep Properties of Si<sub>3</sub>N<sub>4</sub>/SiC Composite Ceramics

Si3N4/SiC composite ceramics containing 20mass% dispersed SiC particles were fabricated by hot-pressing at 1800°C under 35MPa for 2h. SiC powders with average particle sizes of 0.03, 0.27, 0.60 and 1.20μm were used, and the influence of the SiC particle size on the creep properties was investigated. Creep tests were performed by 4-point bending for 100h at 1250-1350°C under 250-450MPa in air. Grain growth in the Si3N4 matrix was prevented by the dispersed SiC particles. The Si3N4 matrix grain size decreased with decreasing SiC particle size. Steady state creep strain rate ε increased with decreasing Si3N4 matrix grain size. Accordingly, the creep properties were not improved by the dispersed SiC particles. Stress exponents, n were 1.5-2.7. It was assumed that the creep deformation was controlled by grain boundary sliding accompanied by cavitation. Moreover, weight gains of Si3N4/SiC composite ceramics were larger than that of monolithic Si3N4 after creep tests. However, the bending strength of Si3N4/SiC slightly increased.

ＳｉＣ粒子分散によるムライトの高温強度特性の向上

ＳｉＣ粒子分散によるムライトの高温強度特性の向上

Room-Temperature Strength and Fracture Toughness of β-Sialon (<i>z</i>=1)-SiC Composite Fabricated from Aluminum-<i>iso</i>-Propoxide, α-Si<sub>3</sub>N<sub>4</sub> and β-SiC

β-sialon (z=1)-SiC (50mass%) composite was fabricated by hot-pressing a spray-dried mixture of α-Si3N4, SiC and aluminum-iso-propoxide solution. The bending strength and fracture toughness (KIC) of sinterd bodies were investigated by comparing with β-sialon (z=1) without SiC. Both strength and KIC were increased from 1000 to 1560MPa and 3.5 to 4.5MPa·m1/2 by SiC addition, respectively. About a half of tested specimens fractured from internal defects and the other fractured from surface flaws. The strength of the specimens which fractured from internal defects increased from 1180 to 1580MPa. This value coincided with that derived from the equation KIC=σfY√c, due to the same size of defects as fracture origins (c). In case of the specimens which fractured from surface flaws, the strength increased from 900 to 1540MPa. The increase in KIC presumably resulted in decreasing the size of machining flaws as fracture origins. It was considered that as the transgranular fracture occurred in the β-sialon matrix of this composite, homogeneously dispersed SiC particles immediately brought small crack deflection. This might be a reason for increase in both strength and KIC.

Synthesis and high temperature mechanical properties of Ti3SiC2/SiC composite

A high density Ti3SiC2/20 vol % SiC composite was hot pressed under a uniaxial pressure of 45 MPa for 30 min in an Ar atmosphere at 1600 °C. The grain size of the Ti3SiC2/SiC composite was finer than that of monolithic Ti3SiC2, though the composite was hot pressed at a higher temperature, due to the dispersion of SiC particles in the Ti3SiC2 matrix. Room temperature fracture toughness of the composite and Vickers hardness were measured as 5.4 MPa m1/2 and 1080 kg mm−2, respectively. A higher flexure strength of the composite compared to that of monolithic Ti3SiC2 was measured both at room temperature and up to 1200 °C. At 1000 °C, the composite showed a lower oxidation rate than that of monolithic Ti3SiC2.

Influence of SiC Particle Size on Microstructure and Mechanical Properties of Si<sub>3</sub>N<sub>4</sub>/SiC Composite Ceramics

Si3N4/SiC composite ceramics containing 20mass% dispersed SiC particles were fabricated by hot-pressing at 1800°C under 35MPa for 2h. SiC powders with average particle sizes of 0.03, 0.27, 0.60 and 1.20μm were used, and the influence of the SiC particle size on the microstructure and mechanical properties (3-point bending strength and fracture toughness values) was investigated. As a result, grain growth and α-β transformation in Si3N4 matrix were prevented by the dispersed SiC particles. The Si3N4 matrix grain size decreased with decreasing SiC particle size, and in Si3N4/SiC (0.03μm) and Si3N4/SiC (0.27μm), α-phase remained. The fracture toughness decreased with decreasing Si3N4 matrix grain size. Accordingly, the fracture toughness was not improved by the dispersed SiC particles. In Si3N4/SiC (0.03μm), the bending strength showed a maximum value of 1161MPa at room temperature and 950MPa at 1400°C. It is considered that the remarkable improvement in the strength of Si3N4/SiC (0.03μm) is attributed to fine grains of Si3N4 matrix. On the other hand, other composites showed almost the same strengths as monolithic Si3N4.

Strengthening of Mullite by Dispersion of Carbide Ceramics Particles. 2nd Report. Effect of SiC grain Size and Heat Treatment.

Mullite composite ceramics contaning 20vol. % dispersed SiC particles (0. 12-1. 71μm) were prepared by hot-pressing at 1650°C under 35MPa for 4h. The effect of dispersed particle size on mechanical properties was investigated. Grain growth of mullite was prevented by the existence of dispersed SiC particles in the matrix, and the matrix grain size of mullite/SiC composites decreased with decreasing dispersed SiC particle size. As a result, bending strength for most mullite/SiC composites increased with decreasing dispersed particle size. In the case of mullite/SiC (0. 56μm), bending stregth showed a maximum value of 626MPa, which was about 60% higher than that of monolithic mullite. The influence of atmosphere of thermal treatment on bending strength of mullite/SiC composites was also investigated. It is concluded that the strengthening by thermal treatment in air was caused by healing of surface flaws in the specimen.

スプレイフォーミング法によるＳｉＣ粒子分散Ｍｇ‐ＣｅおよびＭｇ‐Ｃａ合金複合材料

SiC particulate dispersed Mg-10%Ce and Mg-5%Ca alloy composites were successfully obtained by using an experimentally constructed spray forming apparatus with simultaneous injection of SiC particles. The spray formed composites showed relative density higher than 95%. The relative density was improved to above 99% by hot extrusion. The uniformity in distribution of dispersed SiC particles was also improved by hot extrusion. It has been shown that fine SiC particles which are even smaller than 1μm in diameter can be dispersed by spary forming technique. The measured Vf of SiC particles in spray formed and hot extruded materials increased with an increase of the average particle size. The obtained Vf of coarse SiC particles which is 12μm in average size was as high as 18.8%. The elastic modulus and hardness were appreciably increased by dispersion of SiC particles. However, improvement in tensile strength was not observed in the composites.

Processing SiC-particulate reinforced titanium-based metal matrix composites by shock wave consolidation

SiC particulate reinforced titanium matrix composites have been processed by shock wave consolidation. These materials are difficult to produce using traditional methods because of the high reactivity of titanium with most reinforcement materials. However, using shock consolidation, fully dense composite compacts that are free from interfacial reactions and macroscopic cracks have been obtained. Process variables (starting powder size, dispersion of SiC particles, chemical impurity level, and pre-compaction degassing and heat treatment) have been investigated. Proper post-consolidation annealing has also been explored to improve impurity segregation and, thus, ductility of the matrix. Subsequent heat treatments of the composites produce controlled interfacial reaction zones sizes. The processed materials are ideal for studying effects of interfacial properties on the mechanical behavior of particulate reinforced metal matrix composites.

溶湯攪拌混合法による SiC 粒子分散強化型 AC8A 複合材料の製造および機械的性質

溶湯攪拌混合法による SiC 粒子分散強化型 AC8A 複合材料の製造および機械的性質