Nano-sized SiC Research Articles

Effects of graphite flake diameter on mechanical properties and thermal shock behavior of ZrB2–nanoSiC–graphite ceramics

ZrB2–20vol.% nanoSiC–20vol.% graphite (ZSnpG) ceramics that contained graphite flakes with different diameters were investigated to determine the effects of graphite flake diameter on the microstructure and mechanical properties, as well as thermal shock resistance. The results showed that the flexural strength and relative density of ZSnpG ceramics firstly increased and then decreased with increasing the diameter of graphite, whereas the fracture toughness did not change significantly. The improvement in the flexural strength of ZSnpG ceramics was strongly dependent on the controlling of graphite distribution, the reduction of the length of the microcrack that resulted from thermal residual stress and the presence of intragranular nano-sized SiC particles. The calculated thermal shock parameters revealed that the graphite with finer starting diameter had a beneficial effect on the blocking of the crack initiation and the graphite with larger diameter restrained the crack propagation of ZSnpG ceramics.

Dielectric and EMW absorbing properties of PDCs-SiBCN annealed at different temperatures

Abstract Polymer derived SiBCN ceramics (PDCs-SiBCN) were prepared from polyborosilazane and then annealed at 1200–1800 °C in N 2 . Effects of annealing temperature on the microstructure, phase composition, dielectric and wave-absorbing properties of ceramics were investigated. Results showed that nano-sized SiC grains were formed in amorphous SiBCN after annealing and the content and crystallization degree of SiC gradually intensified with annealing temperature increasing. The permittivity, dielectric loss and electrical conductivity of PDCs-SiBCN gradually increased as the temperature rose due to the formation of conductivity network of SiC grains and the increase of nano-grain boundary. The increased content of SiC (as the dipole) and interface between SiC nano-grains and amorphous SiBCN phase led to a higher polarization ability and higher dielectric loss. The RC gradually decreased with the annealing temperature increasing, demonstrating the annealed ceramics had the superior wave-absorbing ability and high annealing temperature was conducive to the improvement of wave-absorbing property.

Infiltration mechanism of diamond/SiC composites fabricated by Si-vapor vacuum reactive infiltration process

Abstract Dense diamond/SiC composites were fabricated by Si vapor vacuum reactive infiltration of carbon-containing diamond porous preform at 1600 °C for 1 h. The microstructural evolution of the composites was investigated. The infiltration mechanisms during reactive infiltration were discussed. The composite consists of diamond, β-SiC and a small amount of Si. Epitaxial growth of nano-sized SiC on diamond and graphite surfaces occurred due to the diffusion-reaction mechanism in the initial stage of infiltration. Growth of micron-sized SiC with no preferential orientation was controlled by solution-precipitation mechanism in the final stage. The infiltration process was determined both by molecular diffusion and capillary effects. Explosive evaporation of molten Si, volume expansion of the solids and heat release during the reaction were the key factors contributing to the rapid densification of diamond/SiC composites. High thermal conductivity (580 W m −1 K −1 ) and low density (3.33 g cm −3 ) of the composites were beneficial to thermal management applications.

In vitro cellular responses to silicon carbide nanoparticles: impact of physico-chemical features on pro-inflammatory and pro-oxidative effects

Silicon carbide is an extremely hard, wear resistant, and thermally stable material with particular photoluminescence and interesting biocompatibility properties. For this reason, it is largely employed for industrial applications such as ceramics. More recently, nano-sized SiC particles were expected to enlarge their use in several fields such as composite supports, power electronics, biomaterials, etc. However, their large-scaled development is restricted by the potential toxicity of nanoparticles related to their manipulation and inhalation. This study aimed at synthesizing (by laser pyrolysis or sol–gel methods), characterizing physico-chemical properties of six samples of SiC nanopowders, then determining their in vitro biological impact(s). Using a macrophage cell line, toxicity was assessed in terms of cell membrane damage (LDH release), inflammatory effect (TNF-α production), and oxidative stress (reactive oxygen species generation). None of the six samples showed cytotoxicity while remarkable pro-oxidative reactions and inflammatory response were recorded, whose intensity appears related to the physico-chemical features of nano-sized SiC particles. In vitro data clearly showed an impact of the extent of nanoparticle surface area and the nature of crystalline phases (α-SiC vs. β-SiC) on the TNF-α production, a role of surface iron on free radical release, and of the oxidation state of the surface on cellular H2O2 production.

Electrical resistivity of silicon carbide ceramics sintered with 1 wt% aluminum nitride and rare earth oxide

Abstract The influence of additive composition on the electrical resistivity of hot-pressed liquid-phase sintered (LPS)-SiC was investigated using AlN–RE2O3 (RE = Sc, Nd, Eu, Gd, Ho, Er, Lu) mixtures at a molar ratio of 60:40. It was found that all specimens could be sintered to densities >95% of the theoretical density by adding 5 wt% in situ-synthesized nano-sized SiC and 1 wt% AlN–RE2O3 additives. Six out of seven SiC ceramics showed very low electrical resistivity on the order of 10−4 Ω m. This low electrical resistivity was attributed to the growth of nitrogen-doped SiC grains and the confinement of non-conducting RE-containing phases in the junction areas. The SiC ceramics sintered with AlN–Lu2O3 showed a relatively high electrical resistivity (∼10−2 Ω m) due to its lower carrier density (∼1017 cm−3), which was caused by the growth of faceted grains and the resulting weak interface between SiC grains.

Synthesis of Al/SiC nanocomposite and evaluation of its mechanical properties using pulse echo overlap method

In the present study, pulse echo overlap method (PEO) has been used as a non-destructive technique for evaluating the mechanical properties of Al/SiC nanocomposites. The nano-sized AI/SiC powders were prepared by mechanical alloying method. The particle size and microstructures of the milled powders were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) techniques. Al/SiC powders containing different amounts of nano-size SiC particles (0, 5 and 10vol.%) were subsequently cold-pressed and sintered to produce bulk composite samples. The polycrystalline bulk modulus K, Young’s modulus E, shear modulus G, Poisson ratio υ and hardness H of Al/SiC composites are gained by PEO method. The results showed an increase in the hardness value from 3.8 to 6.6GPa and a decrease in Al crystallite size from 175.6 to 90.8nm with increasing SiC content. Besides, Young’s modulus of Al/10SiC sample was measured to be 97.1GPa, which is much higher than that for pure Al (72.6GPa). Poisson’s ratio results indicate that its value decreases with increasing the elastic moduli and ultrasonic wave velocities of Al/SiC composites. The Pugh ratio showed the ductility behavior of all Al/SiC samples, while Poisson’s ratio showed slightly decrease in the ionic contribution with increasing the volume fraction of SiC nanoparticles in metal matrix composites MMCs. Microstructural analysis revealed that the origin of change in mechanical properties is attributed to the decrease in interparticle spacing and increase in the grain boundary area, which provides more obstacles for dislocation pile up in the adjacent grains.

Thermal shock properties of 2D-SiCf/SiC composites

This paper dealt with the thermal shock properties of SiCf/SiC composites reinforced with two dimensional SiC fabrics. SiCf/SiC composites were fabricated by a liquid phase sintering process, using a commercial nano-size SiC powder and oxide additive materials. An Al2O3–Y2O3–SiO2 powder mixture was used as a sintering additive for the consolidation of SiC matrix region. In this composite system, Tyranno SA SiC fabrics were also utilized as a reinforcing material. The thermal shock test for SiCf/SiC composites was carried out at the elevated temperature. Both mechanical strength and microstructure of SiCf/SiC composites were investigated by means of optical microscopy, SEM and three point bending test. SiCf/SiC composites represented a dense morphology with a porosity of about 8.2% and a flexural strength of about 160MPs. The characterization of SiCf/SiC composites was greatly affected by the history of cyclic thermal shock. Especially, SiCf/SiC composites represented a reduction of flexural strength at the thermal shock temperature difference higher than 800°C.

Improvement of the Tool Life of a Micro-End Mill Using Nano-Sized SiC/Ni Electroplating Method

High mechanical properties of a tungsten carbide micro-end-mill tool was achieved by extending its tool life by electroplating nano-sized SiC particles (< 100 nm) that had a hardness similar to diamond in a nickel-based material. The co-electroplating method on the surface of the micro-end-mill tool was applied using SiC particles and Ni particles. Organic additives (saccharin and ammonium chloride) were added in a Watts bath to improve the nickel matrix density in the electroplating bath and to smooth the surface of the co-electroplating. The morphology of the coated nano-sized SiC particles and the composition were measured using Scanning Electron Microscope and Energy Dispersive Spectrometer. As the Ni/SiC co-electroplating layer was applied, the hardness and friction coefficient improved by 50%. Nano-sized SiC particles with 7 wt% were deposited on the surface of the micro-end mill while the Ni matrix was smoothed by adding organic additives. The tool life of the Ni/SiC co-electroplating coating on the micro-end mill was at least 25% longer than that of the existing micro-end mills without Ni/SiC co-electroplating. Thus, nano-sized SiC/Ni coating by electroplating significantly improves the mechanical properties of tungsten carbide micro-end mills.

Fabrication and characterization of heat and plasma treated SiC/Al2O3–YSZ feedstocks used for plasma spraying

The SiC/Al2O3–YSZ (ZrO2 + 8 wt.% Y2O3) powders with different SiC particle sizes were fabricated and treated from spray drying, heat treatment, and plasma spraying. The morphology, phase composition, flowability and density of powders were analyzed. The sphericity and flowability of powders treated by plasma flame are increased greatly, and the particle surface is very smooth. The flowability and density of powder with nano SiC were evident better than those of powder with submicron SiC. The optimum flowability and compactness of powder with submicron SiC is obtained when the critical plasma spray parameter is 341 and 325, respectively. For nano size SiC, the optimum flowability and the maximum compactness of powders are obtained with critical plasma spray parameter of 341. The grain size of powders is increased after heat treatment and plasma spraying. The SiC is oxidized to SiO2 in the powders after heat treatment and plasma spraying. The Y2O3 dissolved from 8YSZ solid solution at higher critical plasma spray parameter. Besides, there is no phase transformation of ZrO2 for powders. The metastable phase of Al2O3 appeared in feedstocks with submicron SiC, but no metastable phase was formed in feedstocks with nano SiC particles, which nano SiC can hinder the formation of Al2O3 metastable phase. The densification process and mechanism of reconstituted particles used for plasma spraying were analyzed from surface morphology, cross section and simulation.

Wear Assessment of Ti/SiC Surface Nano-Composite Layer and its Associated CP-Ti Substrate

In the present investigation, the surface of a commercially pure titanium (CP-Ti) substrate was modified to Ti/SiC nanocomposite layer employing friction stir processing technique; nanosized SiC powder was introduced into the stir zone provided by a rotating and advancing tool. The fabricated nanocomposite surface layer exhibited a micro hardness value of ~535HV which is much greater than 160HV of the substrate material using Vickers micro hardness testing. In addition, the un-treated CP-Ti substrate showed sever wear regime in the pin-on-disc test against the hardened AISI 52100 steel. It suffers extensive typical adhesive wear dominated by plastic deformation as evidenced by scanning electron microscopy. Also, deep grooves were formed, i.e. evidence of abrasive wear. Contrary to this, enhanced wear properties were detected for the Ti/SiC nanocomposite surface layer, i.e. lower coefficient of friction and weight loss. The nanocomposite surface layer was found to be adherent to the underlying substrate during the pin-on-disc test. The superior wear behavior of the nanocomposite surface layer is attributed to its improved micro hardness value due to the presence of hard nanosize SiC particles in a refined titanium matrix.

Wear Assessment of Ti/SiC Surface Nano-Composite Layer and its Associated CP-Ti Substrate

In the present investigation, the surface of a commercially pure titanium (CP-Ti) substrate was modified to Ti/SiC nanocomposite layer employing friction stir processing technique; nanosized SiC powder was introduced into the stir zone provided by a rotating and advancing tool. The fabricated nanocomposite surface layer exhibited a micro hardness value of ~535HV which is much greater than 160HV of the substrate material using Vickers micro hardness testing. In addition, the un-treated CP-Ti substrate showed sever wear regime in the pin-on-disc test against the hardened AISI 52100 steel. It suffers extensive typical adhesive wear dominated by plastic deformation as evidenced by scanning electron microscopy. Also, deep grooves were formed, i.e. evidence of abrasive wear. Contrary to this, enhanced wear properties were detected for the Ti/SiC nanocomposite surface layer, i.e. lower coefficient of friction and weight loss. The nanocomposite surface layer was found to be adherent to the underlying substrate during the pin-on-disc test. The superior wear behavior of the nanocomposite surface layer is attributed to its improved micro hardness value due to the presence of hard nanosize SiC particles in a refined titanium matrix.

FABRICATION OF TI/SIC SURFACE NANO-COMPOSITE LAYER BY FRICTION STIR PROCESSING

In the present investigation, novel Ti / SiC surface nano-composite layer was successfully fabricated by dispersing nano-sized SiC particles into commercially pure titanium plates employing friction stir processing technique. The process parameters such as tool rotation and advancing speeds were adjusted to produce defect-free surface composite layer, however, uniform distribution of the nano-size SiC particles in a matrix of titanium was achieved after the second pass. The micro hardness value of the Ti / SiC nano-composite surface layer was found to be ~534 HV; this is 3.3 times higher than that of the commercially pure titanium substrate. No reaction was detected between SiC powders and the titanium matrix after friction stir processing.

PRODUCING NANOCOMPOSITE LAYER ON THE SURFACE OF AS-CAST AZ91 MAGNESIUM ALLOY BY FRICTION STIR PROCESSING

Friction stir processing (FSP) is an effective tool to produce a surface composite layer with enhanced mechanical properties and modified microstructure of as-cast and sheet metals. In the present work, the mechanical and microstructural properties of as-cast AZ 91 magnesium alloy were enhanced by FSP and an AZ 91/ SiC surface nanocomposite layer has been produced using 30 nm SiC particles. Effect of the FSP pass number on the microstructure, grain size, microhardness, and powder distributing pattern of the surface developed has been investigated. The developed surface nanocomposite layer presents a higher hardness, an ultra fine grain size and a better homogeneity. Results show that, increasing the number of FSP passes enhances distribution of nano-sized SiC particles in the AZ 91 matrix, decreases the grain size, and increases the hardness significantly. Also, changing of the tool rotating direction results much uniform distribution of the SiC particles, finer grains, and a little higher hardness.

AI2O3세라믹스의 강도에 미치는 소결 첨가제 SiC의 함량과 열처리의 영향

In the present study, crack healing effect and residual stress of ceramics were investigated by changing the sintering temperature and heat treatment conditions. And also it was investigated that the influence of different filler loadings of nano-sized SiC particles on the crack healing behavior of ceramics. The test samples were characterized by three point bend flexural tests to evaluate their mechanical properties. The morphological changes were studied by FE-SEM and EDS. The test results indicated that the with nano-sized SiC ceramics sintered at were showed highest density. Sintering temperature at , the bending strength of heat treatment in air atmosphere specimens showed about 42 % increment in comparison to the un-heat treated specimens. The cracked specimens can be healed by heat treatment in vacuum atmosphere but the crack healing effect of ceramics, which is heat treated in air atmosphere was higher than that of heat treated in vacuum atmosphere. with 30 wt% of SiC ceramics indicated higher crack healing ability than that with 15 wt% of SiC ceramics. The FE-SEM images showed that the median cracks and pores were disappeared after heat treatment in air.

Effect of pyrolysis temperature on the pore structure evolution of polysiloxane-derived ceramics

Homogeneous silicon oxycarbide (SiOC) ceramic powders were prepared by pyrolysis of cross-linked polysiloxane at different temperatures (1250–1500°C) under vacuum. The effect of pyrolysis temperature on the pore structure evolution was investigated by means of N2 adsorption, SEM, XRD, IR and element analysis (EA). Studies showed that predominate mesoporous ceramics with the average pore size in the range of 2–13nm were obtained after pyrolysis in this temperature range. The pore structure transformation is strongly correlated with the thermolytic decomposition process of the used precursor, such as phase separation and carbothermal reduction. At relatively lower temperature (1250–1350°C), the ceramics had a relative small specific surface areas (35m2/g) owing to the low degree of carbothermal reduction. However, as the carbothermal degree had an obvious augment at relative higher temperature (1400–1450°C), the specific surface areas and total pore volume increased and reached to the maximum of 66m2/g and 0.214cm3/g, respectively, and subsequently decreased rapidly after 1500°C for the reason of partial sintering of the nano-sized SiC derived from polysiloxane.

PREPARATION OF NANO-SIZED SiC REINFORCED NiTi SHAPE MEMORY COMPOSITES AND THEIR MECHANICAL PROPERTIES AND DAMPING BEHAVIOR

NiTi shape memory alloys have attracted significant attention for applications in various fields in the past decades. Although porous NiTi alloys exhibit lower density compared with the dense ones, they are inevitably lower in strength, storage modulus and damping capacity. Therefore, it is imperative to study and improve the compressive performance and storage modulus in porous NiTi alloys. In this study, the nano-sized SiC particle reinforced NiTi shape memory alloy based composites (SiC/NiTi) have been successfully fabricated by means of a step powder-sintering method, which show unique characteristics of lightweight, high strength and stable superelasticity. The fabricated SiC/NiTi composites possess almost the same equivalent strength compared with dense NiTi alloys. On the other hand, they are in the nature of higher strength, including compressive strength and equivalent compressive strength, than porous NiTi alloys. Furthermore, the strength increases with increasing contents of SiC particles. It has been indicated that the addition of SiC particles has a slight influence on the phase composition of the SiC/NiTi composites, while the martensitic phase transformation temperatures of the composites keep unchanged compared with the NiTi alloy without SiC reinforcement. Meanwhile, the fabricated composites inherit the high damping performance of the NiTi matrix, and thus exhibit a high storage modulus.

The effects of friction-stir process parameters on the fabrication of Ti/SiC nano-composite surface layer

Sound friction-stir processed layers were fabricated on a commercially pure titanium substrate with or without introduction of nano-sized SiC powder to the stir zone under an argon shrouding system using tool rotation and substrate advancing speeds in the range 800–1250 rpm and 35–55 mm/s, respectively. Surface layers exhibited finer grain sizes and greater hardness values compared to those of the as-received substrate. Superior surface enhancements were resulted by uniform dispersion of nano-sized SiC powder in the fabricated surface composite layer after four friction stir process passes. The fabricated Ti/SiC nano-composite surface layer showed a matrix of dynamically restorated ultra fine grains/subgrains with a mean size of ~ 400 nm and a hardness value of ~ 534 HV; this is about 3.3 times greater than that of the as-received substrate.

FABRICATION OF Mg/SiC NANOCOMPOSITE SURFACE LAYER USING FRICTION STIR PROCESSING TECHNIQUE

Friction stir processing (FSP) was employed to incorporate nano-sized SiC particles into the surface of AZ31 magnesium substrate in order to produce surface nanocomposite layers. Characterization of the microstructure of the processed layers exhibited powders agglomeration which was found to disperse with increasing the tool rotation speed/advancing speed ratio. A uniform distribution of SiC particles with a mean particle size of ~95 nm was achieved after second FSP passes. The matrix grain size was found to decrease by increasing the tool advancing speed and number of FSP passes; however, increasing the advancing speed resulted in introduction of defects which leads to tunnels. The micro hardness value of the composite layer with uniform distribution of nano-size SiC particles was found to be almost twice of that of the AZ31 substrate.

Structural investigation of vacuum sintered Cu–Cr and Cu–Cr–4% SiC nanocomposites prepared by mechanical alloying

Abstract Attempts have been made to synthesize Cu 99 Cr 1 , Cu 94 Cr 6 , Cu 99 Cr 1 –4% SiC and Cu 94 Cr 6 –4% SiC (∼30 nm) nanocomposites for thermo-electric applications. The blend compositions were ball-milled for 50 h in a stainless steel grinding media. The microstructural features were characterized by X-ray diffraction (XRD), Nano zeta sizer, Fourier transforms infrared radiation, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Analysis of crystallite size, lattice microstrain and lattice parameter of Cu revealed that the dissolution of Cr increased up to 1 at.% in presence of nanosize SiC particles during milling. The compact specimens were subjected to vacuum sintering (900 °C and 1000 °C for 1 h), and the results were compared with that of microwave sintered samples. The mechanical properties like Vickers hardness and electrical conductivity of the sintered specimens were also investigated.

Fabrication of Al/SiC Nanocomposite Powders via &lt;i&gt;In Situ&lt;/i&gt; Powder Metallurgy Method

In the present investigation, the in-situ powder metallurgy (IPM) method was utilized to synthesis aluminum alloy matrix composite powders containing SiC nanoparticles. Specified amounts of SiC particles (with a size in the range of 250-600 µm) together with SiC nanoparticles (average size of 60 nm) were preheated and added to aluminum melt. This mixture was stirred via an impeller at a certain temperature for a predetermined time. The kinetic energy of the impeller was transferred to the melt via the non-wetting SiC particles and resulted in melt disintegration. The liquid droplets created by this process were then solidified upon cooling the blend resulting in a mixture of Al powders and SiC particles. This blend was passed through a 250 µm sized sieve and a mixture of Al powders and SiC nanoparticles was produced which could be subsequently used as a feedstock for preparation of Al-SiC nano-composites via the standard powder metallurgy methods. The results confirmed that the surface condition (oxidized vs. as-received), amount and different proportions of the added nano-sized and micron sized SiC particles as well as the chemistry of the metallic charge (CP aluminum or Al-1wt.%Mg) affect the size distribution and yield of the resultant sub-250 µm sized powders. The scanning electron microscopy (SEM) studies revealed that Al/SiC composite powders containing nano-sized SiC particles could be produced by using Al-1 wt.% Mg as the matrix alloy.