Sharif Digital Repository

The densification response of aluminum powder reinforced with 5 vol.% nanometric alumina particles (35 nm) during uniaxial compaction in a rigid die was studied. The composite powder was prepared by blending and mechanical milling procedures. To determine the effect of the reinforcement nanoparticles on the compressibility of aluminum powder, monolithic Al powder, i.e. without the addition of alumina, was also examined. It was shown that at the early stage of compaction when the rearrangement of particles is the dominant mechanism of the densification, disintegration of the nanoparticle clusters and agglomerates under the applied load contributes in the densification of the composite powder... 

The compressibility behavior of Al-AlN nanostructured composite powder with different amount of reinforcement content was studied. The composite powder was synthesized by blending and high-energy milling process for 25 h. Williamson-Hall method was applied to determine the crystallite size after milling process. To investigate the role of reinforcement particles in consolidation of composite powders, monolithic aluminum powder was examined. Samples were made at different pressures and relationships were established between the compaction pressure and the density of the compacts. The modified Heckel equation was used to assume the pressure effect on yield strength and then was compared with... 

A zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite) can be a good substitute as reinforcement in metal matrix composites. In the present study, the effect of the amount of 10Ce-TZP/Al2O3 particles on the microstructure and properties of Al/(10Ce-TZP/Al2O3) nanocomposites was investigated. For this purpose, aluminum powders with average size of 30μm were ball-milled with 10Ce-TZP/Al2O3 nanocomposite powders (synthesized by aqueous combustion) in varying amounts of 1, 3, 5, 7, and 10wt.%. Cylindrical-shape samples were prepared by pressing the powders at 600MPa for 60min while heating at 400-450°C. The specimens were then characterized by scanning and... 

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... 

Addition of spinel (MgAl2O4) to Al2O3-ZrO2 composite inhibits alumina grain growth and produces phase boundaries that leads to formation of a ceramic matrix composite with special mechanical properties such as high temperature superplastic deformation. However, the room temperature mechanical properties of Alumina-zirconia-magnesia spinel composite (AZM) such as fracture toughness were rarely investigated by researchers. In this research the AZM nanocomposite powders were synthesized via the solution combustion method. The dense AZM composite samples were fabricated through gelcasting process. Phase analysis studies were performed on both powder and sintered samples and the effects of spinel... 

We have synthesized nanocrystalline MgH2-5at% TiCr1.2Fe0.6 nanocomposite powder by high-energy mechanical alloying for onboard hydrogen storage application. Magnesium hydride and the elemental Ti, Cr, and Ni powders were milled in a SPEX 800 mill under a high purity argon atmosphere. The dehydrogenation properties of the nanocomposite were studied by simultaneous thermal analyzer. The crystallite size of the nanocomposite was determined by XRD method. It is shown that nanometric grain structure, ultrafine particle size, and the catalytic effect of the transition metals possess a relatively low desorption temperature (262 °C) with 5.5wt % hydrogen release for the nanocomposite powder. The... 

Recent advances in material issues for Direct Metal Laser Sintering (DMLS) process are presented. The concept is to decrease the powder particle size with the aim of enhancing the sintering kinetics and improving the surface quality of the produced parts. The outcome is particularly suitable for overcoming existing limitations with the rapid tooling, e.g. manufacturing of mould inserts for injection moulding and die casting, by the DMLS process. The powder composition was adapted near to the conventional P/M steels in order to get identical properties with a favourable price. Such novel powder material provides an opportunity to considerably reduce the product development time for P/M... 

The consolidation behavior of composite powders during pressure cycling at room temperature in uniaxial compaction experiments was studied and compared with monotonic compaction. Aluminum and various amounts of SiC powders (up to 50 vol%) were used to investigate the effect of hard reinforcement particle on the densification of soft aluminum matrix. The cyclic compaction was carried out at various pressure amplitudes, ranges from 90 to 360 MPa, at the frequency of 1 Hz. The pressure cycling was continued up to 5000 cycle, in which, the rate of consolidation was found to be fairly low. The consolidation of the composite powders under different loading modes was analyzed through... 

Carbon nanotubes with unique physical and mechanical properties have shown great potential for biological applications, including tissue engineering and mimicking the structure and properties of human bones. In the present work, sol-gel synthesized nanocomposite powder of multi-wall carbon nanotube/hydroxyapatite characterized using field-emission scanning electron microscopy, transmission electron microscope, X-ray diffraction, Fourier transform infra-red spectroscopy and thermal analyses. The results show homogenous dispersion of nanotube in well-crystallized hydroxyapatite ceramic matrix. Scanning electron microscopy and transmission electron microscope observations show the sodium... 

Effect of Al2O3 nanoparticles (80 nm) on the grain structure and phase formation in Ni-50Ti system during high-energy mechanical alloying (MA) was studied. While the formation of NiTi B2 phase occurs progressively during MA, it is shown that the hard inclusions cause abrupt phase formation at short milling times, particularly at higher nano-Al 2O3 contents. High-resolution transmission electron microscopy showed significant grain refinement in the presence of alumina nanoparticles to sizes less than 10 nm, which precedes the formation of semicrystalline structure and reduces the diffusion length and thus accelerates the phase formation. The composite powder reached steady-state MA condition... 

FeNiCo base powder alloy with nominal composition Fe-27Ni-17Co-4Ti (wt%) was prepared from elemental powders by mechanical alloying. The structure of milled powders was characterized by XRD and SEM. The effect of nanosize structure on magnetic properties and shape memory behavior was studied using VSM and DSC. After milling for 240 minutes by high energy vibrational ball mill under argon atmosphere, supersaturated solid solution formed with mean crystallite size of ∼20 nm. Results of VSM examinations showed that by milling for 240 minutes saturation magnetization and intrinsic coercivity reached 304 emu/gr and 21 Oe, respectively. XRD analyses made it clear that transformation from BCC to... 

Accumulative roll bonding (ARB) is used as a novel method to produce particle reinforced metal matrix composites (MMCs). Roll bonding of the sheets with layers of powder on their surfaces is the main stage in this process and it has been found that quality of the bonding has an important role in properties of the product. In this work, the behavior of alumina particles layer at interface during the rolling is investigated and the effects of particle size and amount of particle at interface on bonding of the commercial pure aluminum sheets are also studied. The results of peeling test indicate that presence of the powder at interface reduces the bond strength. However, it is shown that by... 

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... 

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... 

Compressibility of a nanostructured Al-5AlN composite powder synthesised via high energy ball milling for various times was studied by means of a modified Heckel equation. Since workhardening and morphological changes take place by milling evolution, the compressibility was consequently affected. Strengthening of composite compacts was influenced by milling and compaction processes, i.e. strength of compacts increased at longer milling times and higher compaction pressures. It was found that, at the initial stages of milling and higher compaction pressures, the strengthening was mostly affected from compaction process, whereas the milling strengthening fraction was near to unity at lower... 

A tensile-compression fatigue response of Al matrix composites containing different amount of SiC nanoparticles (50 nm diameter) up to 6 vol. pct was studied. The nanocomposite powders were prepared by a powder metallurgy (P/M) route consisting of mechanical alloying, hot extrusion, and hot closed-die forging. The microstructure of the materials was evaluated by optical microscopy, scanning and transmission electron microscopies, and electron backscattered diffraction. A fine distribution of the nanoparticles in submicron and ultrafine grains was obtained. The low cycle fatigue behavior was examined in stress control mode under fully reversed tension-compression cycle at 1 Hz up to 1000... 

Copper matrix composites reinforced with TiO2particles are promising materials widely used as contact materials due to their excellent mechanical and physical properties such as good electrical and thermal conductivity and strength at high temperature. In this research, the novel contact material were prepared by in-situ oxidation of Cu-Ti pre alloyed powders. The morphology of milled powders and microstructure of nano-composite specimens were studied by SEM and TEM. To evaluate mechanical alloying progress of Cu and Ti powders mixture and internal oxidation after Cu2O addition, XRD analysis were carried out. The Physical and mechanical properties results of specimens indicate that the... 

A neural network (ANN) model was developed to predict the densification of composite powders in a rigid die under uniaxial compaction. Al-SiC powder mixtures with various reinforcement volume fractions (0-30%) and particle sizes (50 nm to 40 μm) were prepared and their compressibility was studied in a wide range of compaction pressure up to 400 MPa. The experimental results were used to train a back propagation (BP) learning algorithm with two hidden layers. A sigmoid transfer function was developed and found to be suitable for analyzing the compressibility of composite powders with the least error. The trained model was used to study the effect of reinforcement particle size and volume... 

In this study, the inclusion of multi-walled carbon nanotubes as the second phase in the hydroxyapatite matrix, in order to improve the mechanical strength, has been performed via the sol-gel process. The stability of carbon nanotube sol with the changes of pH and dispersant values (sodium dodecyl sulfate) was evaluated by zeta potential analysis. The results indicated that synthesis of hydroxyapatite particles in the presence of the carbon nanotubes had the best result in homogenization of the carbon nanotube dispersion and faster crystallization of hydroxyapatite. The crystallization of hydroxyapatite phase was investigated with differential scanning calorimetry (DSC) and X-ray diffraction... 

A modified plastic yield function is proposed to predict the consolidation behavior of nanostructured metal powders and metal-matrix nanocomposite powders under uniaxial compaction. The validity of the model is verified for nanocrystalline Al6063 (~100nm) alloy reinforced without and with 0.8vol.% Al2O3 nanoparticles (~25nm). The plastic deformation propensity of these powders is analyzed by linear compaction equations. The yield stress of the powder compacts is shown to be influenced by the nano-scale grains and the reinforcement nanoparticles