SiC Nanocomposite Powders Research Articles

A novel approach for dynamic compaction of Mg–SiC nanocomposite powder using a modified Split Hopkinson Pressure Bar

ABSTRACTIn this paper, fabrication and characterisation of Mg–SiC nanocomposite are investigated. Micrometre-sized Mg powder with the different volume fraction of SiC nano particles were dynamically compacted using a modified Split Hopkinson Pressure Bar. Moreover, the compaction process was simulated using AUTODYN commercial software to demonstrate that the stress in the powder sample was sufficient for consolidation. To achieve the best quality samples, the effects of lubrication and compaction velocity on dynamic compaction process were initially studied by experiment. It was observed that the temperature of 450°C and the compaction velocity of 15.5 m/s led to the best samples with relative density more than 99%. The effects of reinforcing phase content on the relative density, micro-hardness, and compressive behaviour of the compacted samples along with their microstructures were investigated. The results showed that the micro-hardness and the compressive strength of the samples fabricated at 450°C increased about 70% and 50%, respectively.

Microstructural Characterization of Mg-SiC Nanocomposite Powders Fabricated by High Energy Mechanical Milling

Mg–SiC nanocomposite powders, with SiC particles of 50 nm size, were synthesized by mechanical alloying starting from a mixture of 80 vol.% pure Mg and 20 vol.% SiC powders. The effect of milling time on the microstructure properties of nanocomposite powders during mechanical alloying was investigated. The structural evolution during milling was monitored using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray mapping and X-ray diffraction methods. Using the Williamson-Hall equation, crystallite size and lattice strain of nanocomposite powders were estimated with broadening of XRD peaks. XRD results showed that the crystallite size of magnesium reached 49.52, 15.76 and 12.73 nm, respectively after 5, 15 and 25 h milling, also a uniform distribution of the SiC reinforcement in the Mg matrix was successfully obtained after milling the powders for 25 h.

Microstructures and tensile mechanical properties of an ultrafine grained AA6063–5 vol%SiC metal matrix nanocomposite synthesized by powder metallurgy

A bulk ultrafine grained (UFG) AA6063–5vol%SiC metal matrix nanocomposite has been synthesized by consolidation of a nanocrystalline AA6063–5vol%SiC nanocomposite powder using two powder metallurgy (PM) routes: one combining spark plasma sintering (SPS) and hot extrusion and the other combining die pressing and hot extrusion. The yield strength, ultimate tensile strength and elongation to fracture of the sample produced by a combination of SPS and hot extrusion at 500°C are 392MPa, 496MPa and 7.1%, respectively, while those of the sample produced by die pressing and hot extrusion are 449MPa, 526MPa and 3.5%, respectively. Pre-sintering of the powder compact using SPS prior to extrusion improves the ductility of the consolidated material without causing significant decrease of strength, suggesting that SPS has a beneficial effect on improving the consolidation level of the material. The UFG microstructure of the AA6063 matrix is the result of recrystallization of the as-milled nanocrystalline AA6063–5vol%SiC nanocomposite powder particles during extrusion. With increasing the extrusion temperature from 500 to 550°C, the average grain size of the consolidated sample increases from 276nm to 627nm, leading to a significant decrease of the yield strength from 449 to 233MPa, but a drastic increase of the elongation to fracture from 3.5% to 9.6%.

Phase and morphology studies of B4C–SiC nanocomposite powder synthesized by MASHS method in B2O3, Mg, C and Si system

In this study, ultra fine B4C–SiC composite powder was prepared by mechanically activated self-propagating synthesis (MASHS) method from the raw material of B2O3, Si, C and Mg. Initially the synthesized samples contained MgO, B4C, SiC and a small amount of magnesium borates, residual carbon and silicon. XRD analysis after acid leaching of combustion products showed a great effect of acid leaching on removing the impurities. The remaining substances significantly reduced by increasing the energy of milling. The comparison of diffraction patterns after synthesis and after acid leaching showed that acid leaching had moved the peaks to the lower angles. This is due to the development of solid solution and a decrease in contraction stress during the synthesis. Optimum sample prepared with milling parameter of ball to powder ratio of 20:1, rotation speed 300rpm and milling time of 12h and synthesized at 1000°C furnace temperature. The average crystallite size of B4C and SiC were calculated less than 15nm. These values are consistent with the TEM results while most of grain size was less than 30nm. The particle size analysis of optimum sample indicated that 99.7% of synthesized nanocomposite agglomerated particles were less than 1000nm.

Synthesis and structural evolution of B4C–SiC nanocomposite powders by mechanochemical processing and subsequent heat treatment

B4C–SiC nanocomposite powders were synthesized successfully through mechanochemical processing with B4C, Si and graphite powders. Structural evolution of the powder mixtures was characterized by XRD and IR spectra. Microstructure investigations of the end products were performed in HRTEM. Phase transition of the end products associated with heat treatment was monitored by DSC and XRD. The results indicate that the end products are composed of nanocrystalline B4C and amorphous SiC. The synthesis of the amorphous SiC is only controlled by the gradual diffusion reaction mechanism. During ball milling, the C atoms are firstly dissolved into the interstices of Si lattice to form an interstitial solid solution Si (C). After continuous milling, the C atoms located into the interstices of Si lattice gradually occupy the positions of Si to form amorphous SiC. However, no C or Si atom is dissolved into the interstices of B4C lattice. The large quantity of B4C dilutes the reactants of graphite and Si and hinders the self-propagating reaction to form crystal SiC. The end products (nanocrystalline B4C and amorphous SiC) are gradually transformed into crystalline B4C and SiC during heat treatment.

Effect of starting composition on formation of MoSi2–SiC nanocomposite powder via ball milling

MoSi2–SiC nanocomposite powders were successfully synthesized by ball milling Mo, Si and graphite elemental powders. Effects of milling time and annealing temperature were also investigated. The composite formation and phase transformation were monitored by X-ray diffraction. The microstructure of milled powders was studied by SEM, TEM and XRD peak profile analysis. Formation of this composite was completed after 10 and 20 h of milling for 25%SiC and 50%SiC, respectively. High temperature polymorph (HTP) of MoSi2 was obtained at the end of milling (20 h). On the other hand, annealing led to transformation of HTP to low temperature polymorph (LTP) of MoSi2. Mo5Si3 was formed during annealing as a product of a reaction between MoSi2 and excess graphite. Mean grain size <50 nm was obtained for 20 h milled sample on the basis of peak profile analysis and TEM images.

Artificial Neural Network-Based Multiobjective Optimization of Mechanical Alloying Process for Synthesizing of Metal Matrix Nanocomposite Powder

The aim of this article was to optimize the mechanical alloying process for synthesizing of Al-8vol%SiC nanocomposite powders through an artificial neural network based on multiobjective optimization procedure. First, a suitable trained multi-layer perceptron (MLP) neural network was established for modeling purpose. Process variables as inputs of the network included milling time, milling speed, and balls to powders weight ratio. Parameters of the nanocomposite as outputs of the network were the crystallite size and the lattice strain of the aluminum matrix. The optimization was carried out by using two methods: gradient descent and pattern search. The aim of the optimization was to determine the minimum crystallite size and the maximum lattice strain of the aluminum matrix that could be obtained by regulating the mechanical alloying process variables. The response surfaces and the contour plots showed that the combination of the artificial neural network (ANN) and the optimization procedure were able to optimize the mechanical alloying process to synthesize Al-8vol%SiC nanocomposite.

Mechanochemical synthesis of MoSi2–SiC nanocomposite powder

MoSi2–25wt.%SiC nanocomposite powder was successfully synthesized by ball milling Mo, Si and graphite powders. The effect of milling time and annealing temperature were investigated. Changes in the crystal structure and powder morphology were monitored by XRD and SEM, respectively. The microstructure of powders was further studied by peak profile analysis and TEM. MoSi2 and SiC were synthesized after 10h of milling. Both high and low temperature polymorphs (LTP and HTP) of MoSi2 were observed at the short milling times. Further milling led to the transformation of LTP to HTP. On the other hands, an inverse HTP to LTP transformation took place during annealing of 20h milled powder at 900°C. Results of peak profile analysis showed that the mean grain size and strain of the 20h milled powder are 31.8nm and 1.19% that is in consistent with TEM image.

Dispersion and co-dispersion of ZrB2 and SiC nanopowders in ethanol

The dispersion and co-dispersion behavior of ZrB2 and SiC nanopowders in ethanol solution was studied by sedimentation test, particle size measurement and transmission electron microscope (TEM) analysis. The dispersion behavior of ZrB2 and SiC nanopowders in ethanol solution was strongly dependent on the pH values, types and amounts of dispersant. PEI was found to be effective for the dispersion of both ZrB2 and SiC nanopowders in ethanol solution. With the addition of PEI, the isoelectric points of ZrB2 and SiC nanopowders in ethanol solution were at pH 10 and pH 9.5, and shift to pH 13 and pH 12.3, respectively. The stability of ZrB2 suspension increased with the dispersant content increasing until reached 0.7wt% and well-dispersed SiC slurry can be obtained with more than 2.5wt% PEI. The suitable pH value for the dispersion of ZrB2 and SiC nanopowders should be lower than 12 and 10, respectively. The well co-dispersed ZrB2 and SiC nanocomposite powders can be achieved by using 1wt% or more PEI below pH 10.

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.

Structural and morphological evaluation of Al–5 vol.%SiC nanocomposite powder produced by mechanical milling

Al–5 vol.%SiC nanocomposite powder is produced by using attrition milling in this investigation. The particle size distribution has been determined based on the standard deviation and the coefficient of variation. The results show that the addition of hard SiC particles accelerates the milling process, leading to faster work hardening rate and fracture of the aluminum matrix. Furthermore, Al becomes smaller crystallite size during ball milling of Al powder in the presence of SiC particles. Finally, the scanning electron microscopy (SEM) analysis and the X-ray diffraction (XRD) experiments are used to investigate the effect of milling time on the structural changes of Al–5 vol.%SiC nanocomposite and pure aluminum powder.

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.

The Effect of Reinforcement Phase on the Microstructure of Al-SiC Nanocomposite Powder Prepared via Mechanical Alloying

Mechanical alloying is one of the most successful methods for the manufacturing of metal matrix nanocomposite powders. In this study, Al/SiC metal matrix composite (MMCp) powders with volume fractions of 5, 10, and 15 percent SiC were successfully obtained after milling the powder for a period of 25 hours at a ball to powder ratio of 15:1 using high energy planetary milling. The Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses were conducted to investigate the lattice strain of the matrix phase and the microstructure of the nanocomposite powders after 1, 10, and 25 hours of milling time. Also, the morphology of the Al-5%SiC nanocomposite powder was investigated using transmission electron microscopy (TEM). The results show that with the increase of both milling time and the reinforcement phase volume fraction, the lattice strain increases and the average size of aluminum phase crystallites decreases. Eventually, after 25 hours of milling, the nanocomposite powders show a spherical-like morphology and SiC particles were distributed in an aluminum matrix with appropriate order.

Effect of reinforcement volume fraction on mechanical alloying of Al–SiC nanocomposite powders

Mixtures of aluminium powder and nanoscaled SiC particles (n-SiC) at various volume fractions of 0, 1, 3, 5, 7 and 10 are comilled in a high energy planetary ball mill under an argon atmosphere to produce nanocrystalline Al–SiC nanocomposites. High resolution scanning electron microscopy (HRSEM), X-ray diffraction (XRD) method, laser particle size analysis and powder density measurement were used to study the morphological changes and microstructural evolution occurred during mechanical alloying. Al–SiC composite powder with microscaled SiC particles (1 m m) was also synthesised and characterised to examine the influence of reinforcement particle size on the milling process. It was found that with increasing volume fraction of n-SiC, a finer composite powder with more uniform particle size distribution is obtained. The morphology of the particles also became more equiaxed at shorter milling times. Furthermore, the analysis of XRD patterns by Williamson–Hall method indicated that the crystallite size of the aluminium matrix decreases with increasing reinforcement volume content while the lattice strain changes marginally. As compared with microscaled SiC particles, it appeared that the effect of n-SiC on the milling stages is more pronounced. The results clearly show that the reinforcement particles influence the work hardening and fracture of the metal matrix upon milling, affecting the structural evolution. With decreasing size of the ceramic particles to nanoscale, this influence becomes more pronounced as the surface to volume fraction increases.

Artificial neural network modeling of mechanical alloying process for synthesizing of metal matrix nanocomposite powders

An artificial neural network model was developed for modeling of the effects of mechanical alloying parameters including milling time, milling speed and ball to powder weight ratio on the characteristics of Al–8 vol%SiC nanocomposite powders. The crystallite size and lattice strain of the aluminum matrix were considered for modeling. This nanostructured nanocomposite powder was synthesized by utilizing planetary high energy ball mill and the required data for training were collected from the experimental results. The characteristics of the particles were determined by X-ray diffraction, scanning and transmission electron microscopy. Two types of neural network architecture, i.e. multi-layer perceptron (MLP) and radial basis function (RBF), were used. The steepest descent along with variable learning rate back-propagation algorithm known as a heuristic technique was utilized for training the MLP network. It was found that MLP network yields better results compared to RBF network, giving an acceptable mapping between the network responses and the target data with a high correlation coefficients. The response surfaces between the response variables, i.e. crystallite size, lattice strain of the aluminum matrix and the processing parameters are presented. The procedure modeling can be used for optimization of the MA process for synthesizing of nanostructured metal matrix nanocomposites.

Processing Ti3Al–SiC nanocomposites using high energy mechanical milling

Abstract Ti 3 Al–10 vol.% SiC and Ti 3 Al–20 vol.% SiC composite powders were produced by high energy mechanical milling of Ti, Al and SiC powders, using both coarse and fine SiC powders. For a coarse SiC powder, the milling energy has to be high enough to fracture the SiC particles in-situ. While for a fine SiC powder, a lower energy mill is sufficient to produce a nanocomposite powder. Additionally, nanocrystalline Ti(Al) solution was formed during milling. A simple theoretical analysis shows that there exists a lower limit of the particle size below which further reduction of the particle size cannot be achieved by milling since the stresses required for further particle refinement cannot be reached during milling. During consolidation of the Ti 3 Al–SiC nanocomposite powders, the reaction between the Ti 3 Al matrix and SiC is difficult to be avoided.

Effect of Y2O3 addition on ammono sol–gel synthesis and sintering of Si3N4–SiC nanocomposite powder

Abstract An ammono sol–gel and carbothermal reduction process was employed to prepare silicon nitride–silicon carbide (Si 3 N 4 –SiC) nanocomposite powder using silica sol, urea and carbon black as starting materials. When yttria (Y 2 O 3 ) was introduced into the silica sol, a Si 3 N 4 –SiC–Y 2 O 3 composite powder was obtained. Results showed Y 2 O 3 addition led to substantial change in the synthesizing temperature and the morpyology and size of Si 3 N 4 –SiC powder. The state of Y presented in Si 3 N 4 –SiC composite powder was investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The effect of addition method and amount of additives on densification and microstructure of sintered Si 3 N 4 –SiC ceramics was examined. In comparison with mixed powders of Si 3 N 4 –SiC and Y 2 O 3 , the evaluated densification of Si 3 N 4 –SiC–Y 2 O 3 composite powder can be carried out with a smaller amount of Y 2 O 3 , since Y 2 O 3 was dispersed more homogeneously with Si 3 N 4 –SiC.