Sharif Digital Repository

An architectural modification method was utilized to improve fracture toughness of discontinuously reinforced aluminum (DRA) composites. Al-DRA composites having a structure similar to that of reinforced concrete were fabricated. The number of reinforcing DRA rods within Al matrix and volume fraction of SiC particles in DRA were altered to evaluate their effect on fracture behavior of these materials. It was found that architectural modification does not have any destructive influence on elastic modulus and yield strength of the composite. Moreover, the success of this method on toughness improvement strongly depends on the occurrence of debonding between Al and DRA regions upon loading  

In this study Al2O3-SiC micro/nanocomposites have been fabricated by mixing alumina nanopowders and silicon carbide micro/nanopowders, followed by hot pressing at 1550, 1600, 1650 and 1700°C. The density, mechanical properties and fracture mode of Al2O3-SiC composites containing different volume fractions (2.5%, 5%, 7.5%, 10% and 15%) of micro/nanoscale SiC particles were investigated and compared with those of alumina. The relative density of composites could reach values very close to theoretical density, especially after sintering at 1700°C. However, relative density declined by increasing the SiC fraction at the same sintering temperature. The flexural strength of composites was best for... 

Foaming and crystallisation behaviours of compacted glass powders based on a diopside glass-ceramic composition were investigated using the sintering route. The foaming agent was 2 wt.% SiC particles. The effect of PbO on the foaming ability of glasses was investigated. The results showed that the addition of PbO not only improved the foaming ability, by improving the wettability of the glass-SiC particles but also increased the crystallisation temperature and widened the temperature interval between the dilatometric softening point and the onset of crystallisation. The glass-SiC wetting angle was decreased from 85°for the lead-free glass, to 55°for the glass that contains 15 wt.% PbO  

Cu-Sn composites incorporated with graphite and/or SiC particles were produced by electrodeposition technique. The effect of particle concentration in the plating bath and current density on tin content and volume percentage of particles in the coatings has been investigated. Structure, morphology, micro hardness and wear properties of the coatings have been studied. The results showed that particles cause an increase of tin content in the plated Cu-Sn. Graphite and silicon carbide particles had different effects on coating hardness; 7.8. vol.% graphite decreased the hardness of Cu-Sn layer from 231. Hv to 172. Hv whereas, 5.1. vol.% SiC raised the hardness to 316. Hv. Moreover, friction... 

In order to investigate the dislocation structure and flow stress evolution of Al-SiCp composite during ARB process, a comprehensive model which describes the evolution of dislocation density is needed. Dislocation density, microstructure and flow stress evolution of Al-SiCp composite are predicted considering the ETMB model, strain and strain rate achieved from the mechanical model of ARB process and shear modulus calculated from the composite model. In addition, models' parameters such as dislocation generation parameters are modified due to the effect of SiC particles. The predicted results are in good agreement with experimental data  

Burr in drilling plays an important role on product quality, so analysis the burr height is essential at the final production. This paper presents the application of Taguchi method for survey the burr height by adding ultrasonic vibration to the process. In this paper L18 orthogonal array based on Taguchi techniques was used in the design of experiments. Analysis of Variance (ANOVA) was used to determination the effect of drilling parameter on burr formation. Influence of spindle speed, feed rate and percentage of SiC particle was investigated in with and without ultrasonic assisted drilling. In this paper drilling of Al/SiCp MMCs with 5, 15 and 20 wt% of particulate SiC in dry drilling... 

Crystallographic texture is one of the most sensitive parameters for controlling the microstructure of electrodeposited layers. In this work, we study the crystallographic texture of electrodeposited nickel-silicon carbide coatings. The nickel coatings containing SiC nanoparticles and microparticles were electrodeposited from an additive-free sulfate bath containing nickel ions and SiC particles. The effect of current density on the codeposited Ni/SiC was studied. The coatings were analyzed with scanning electron microscopy and X-ray diffraction. Pole figure studies were done to characterize the evolved crystallographic texture. The X-ray scans followed by Rietveld analysis using the... 

In the present research the aging behavior of Al6061 alloy and Al6061/SiCp composite fabricated by powder metallurgy method was investigated. The solution treatment of the samples were carried out at 527°C for 2, 3and 4 h followed by aging at 180°C for different aging times between 1 and 10 h. The existence of SiC particles led to increasing the peak hardness of the composite. The peak hardness of the composite took place at shorter times than that of the 6061 alloy for the samples solution treated for 3and 4 h, but took place at longer times for the samples solution treated for 2 h. The optimum solution treating time was about 3 h for both the composite and the 6061 alloy that led to the... 

Metal matrix composites (MMCs) have received considerable attention due to their excellent engineering properties. However, poor machinability has been the main deterrent to their substitution for metal parts. The hardness and abrasive nature of reinforcement phase causes rapid tool wear during machining which results in high machining costs. In this study, the effect of SiC particles (5, 15 & 20 percent) on tool wear in turning process is experimentally investigated. Continuous dry turning of Al/SiC particulate metal matrix composite produced by powder metallurgy and utilizing titanium carbide inserts has been achieved as the test method. The influence of machining parameters, e.g. cutting... 

Al2O3-SiC composite ceramics were prepared by pressureless sintering with and without the addition of MgO, TiO2 and Y2O3 as sintering aids. The effects of these compositional variables on final density and hardness were investigated. In the present article at first α-Al2O3 and β-SiC nano powders have been synthesized by sol-gel method separately by using AlCl 3, TEOS and saccharose as precursors. Pressureless sintering was carried out in nitrogen atmosphere at 1600 °C and 1630 °C. The addition of 5 vol.% SiC to Al2O3 hindered densification. In contrast, the addition of nano MgO and nano TiO2 to Al 2O3-5 vol.% SiC composites improved densification but Y2O3 did not have positive effect on... 

This article reports experimental results on laser sintering of A356 aluminum alloy and A356/SiC composite powders. Effects of scan rate, sintering atmosphere, hatch spacing, and SiC volume fraction (up to 20%), and particle size (7 and 17 μm) on the densification were studied. The phase formation and microstructural development were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). Laser sintering under argon atmosphere exhibited higher densification compared to nitrogen. A faster sintering kinetics was observed as the scan rate decreased. Except at a low SiC content (5 vol%), the composite powders exhibited... 

Ni-Co/SiC composite coatings with various contents of SiC particles were electrodeposited in a modified Watt's type of Ni-Co bath containing suspended 20 nm SiC particles. Deposition parameters including current density, bath SiC concentration and magnetic stirring rate were optimized for the highest amount of the SiC codeposition: the current density of 4 A/dm2, 40 g/dm 3 SiC concentration and 480 rpm stirring rate. In order to study the SiC particles codeposition, the Guglielmi's model of codeposition was modified for high volume percentages of the second phase and the modified model was employed to explain the effects of deposition parameters on the kinetics of the particles codeposition.... 

In the present research work the 2024 aluminum alloy was reinforced with SiC particles via powder metallurgy method. The effect of heat treatment conditions on artificial aging kinetics was investigated. The solution treatment of the composite sample and the unreinforced alloy was carried out at 495 °C for 1, 2 and 3 h followed by aging at 191 °C for various aging times between 1 and 10 h. The existence of SiC particles led to increasing the peak hardness of the alloy. The peak hardness of the composite sample took place at shorter times than that of the unreinforced alloy for the samples solution treated for 2 and 3 h, but took place at longer times for the samples solution treated for 1 h.... 

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... 

The aim of the present work is to study the effect of reinforcement content and sintering temperature on the densification and microstructural development during sintering of Al6061/SiC composite compacts. Prealloyed Al6061 powder was mixed with various amounts of SiC particles up to 27 vol.-% and compacted at 350 MPa. Sintering was carried out in a dry nitrogen atmosphere at 580-620°C. It was shown that the presence of SiC particles retards the densification of the prealloyed powder during solid phase sintering and liquid phase sintering. This effect is particularly noticeable at SiC fractions higher than ∼9 vol.-%, at which continuous networks of the hard particles are formed. Increasing... 

The consolidation behaviour of particulate reinforced metal matrix composite powders during cold uniaxial compaction in a rigid die was studied. Al-SiC powder mixtures with varying SiC particle size, ranging from nanoscale (50 nm) to microscale (40 μm), at different volume fractions up to 30% were used. Based on the experimental results, the effect of the reinforcement particles on the densification mechanisms, i.e. particle rearrangement and plastic deformation, was studied using modified Cooper-Eaton equation. It was found that by increasing the reinforcement volume fraction or decreasing its size, the contribution of particle rearrangement on the densification increases while the plastic... 

Ni-Co/SiC nanocomposite coatings were electrodeposited in a modified watt type of Ni-Co bath containing 20 nm SiC particles to be codeposited. Potentiodynamic polarization tests were conducted to study the effect of the SiC particulates on the electrodeposition of Ni and Co. Scanning electron microscopy was used to assess the morphology of the Ni-Co alloy and Ni-Co/SiC nanocomposite coatings. The distribution of the particulates in the matrix was considered by means of transmission electron microscopy. Applying nanomechanical testing instruments coupled to atomic force microscopy, mechanical properties of the alloy and composite coatings were studied and compared. The presence of 11 vol.%... 

In the present article, α-Al2O3 nano powder was synthesized by a simple aqueous sol-gel method by using AlCl3 as precursor. It was shown that the gel calcined at 1000°C, 1100 °Cand 1200 °Cresulted in the formation of a crystalline ?-Al2O3 nano powder. In continue TEOS and saccharose was used to prepare SiO2 xerogels containing carbon nano particles. The conversion of the gel to β-SiC nano powders was accomplished by carbothermal reduction at 1500°Cfor 1 h in argon atmosphere. In second pace alumina matrix composites with nano particles of 5 vol% SiC were prepared with the addition of TiO 2 as sintering aid and densified by pressureless sintering method at 1600°Cand 1630°C for 2 h in nitrogen... 

Friction and wear behaviors of artificially aged 2024 Al and 2024 Al/20 vol.% SiC composite prepared by powder metallurgy method were investigated in the temperature range 20250 °C. Dry sliding wear tests were conducted at a constant sliding velocity of 0.5 m/s, an applied load of 20 N, and a sliding distance of 2500m using a pin-on-disc apparatus. Worn surfaces and wear debris were also examined by using SEM and EDS techniques. All specimens showed a transition from mild-to-severe wear above a critical temperature. In the mild wear regime, the wear rate and the friction coefficient of the composite specimen were higher than those of the unreinforced alloy. The SiC particles led to an... 

Alg -(1, 3, 5, 7, 10 vol%) SiC nanocomposites were produced by mechanical alloying (MA) and double pressing/sintering route. The characteristics of the milled powders and the consolidate specimens were examined using high resolution scanning electron microscopy and X-ray diffraction method. Compression and hardness tests were used to study the effect of SiC volume fraction on the strength of Alg -SiC nanocomposites. It was shown that with increasing the SiC volume fraction, finer particles with narrower size distribution and smaller crystallite size are obtained after MA. During sintering close to the melting point of aluminum, the presence of nanometer-scaled SiC particles was found to...