Carbon Nanotubes Reinforced Aluminum Matrix Composites - A Review of Processing Techniques

Carbon nanotube reinforced aluminium matrix composites (Al-CNTs) have been widely used in aerospace and automotive industries where high quality and strength is required. The enhanced mechanical properties of Al-CNTs are closely related to processing technique due to challenges within production of these composite materials. In the current review, solid state processing techniques used for synthesizing Al-CNTs have been reviewed to provide an insight into the features and capabilities of each technique regarding the incorporation of CNT reinforcements. To conclude, the mechanical performance of Al-CNT composites is mainly decided by the capability of each technique in the dispersion of CNTs within the aluminum matrix

Investigation of the structure and hardness of quenched sintered materials produced from iron-base alloyed powders (Astaloy E)

The effect of heat treatment on the microstructure, hardness and density of sintered (1129°C, 45 min) specimens of iron-base powder alloys containing 0.8 – 2.5% C, 2% Cu and additives of chromium- and molybdenum-alloyed Astaloy E iron powder is studied

Effect of artificial aging on the microstructure and mechanical properties of aluminum alloy AA6061-T6

The properties of aluminum alloy AA6061-T6 after aging at 220°C for 0.5 – 8 h are studied by the methods of light and scanning electron microscopy and fractography. The mechanical characteristics of the alloy are determined by tensile tests

Process−microstructure−properties relationship in Al−CNTs−Al2O3 nanocomposites manufactured by hybrid powder metallurgy and microwave sintering process

Al−2CNTs−xAl2O3 nanocomposites were manufactured by a hybrid powder metallurgy and microwave sintering process. The correlation between process-induced microstructural features and the material properties including physical and mechanical properties as well as ultrasonic parameters was measured. It was found that physical properties including densification and physical dimensional changes were closely associated with the morphology and particle size of nanocomposite powders. The maximum density was obtained by extensive particle refinement at milling time longer than 8 h and Al2O3 content of 10 wt.%. Mechanical properties were controlled by Al2O3 content, dispersion of nano reinforcements and grain size. The optimum hardness and strength properties were achieved through incorporation of 10 wt.% Al2O3 and homogenous dispersion of CNTs and Al2O3 nanoparticles (NPs) at 12 h of milling which resulted in the formation of high density of dislocations and extensive grain size refinement. Also both longitudinal and shear velocities and attenuation increase linearly by increasing Al2O3 content and milling time. The variation of ultrasonic velocity and attenuation was attributed to the degree of dispersion of CNTs and Al2O3 and also less inter-particle spacing in the matrix. The larger Al2O3 content and more homogenous dispersion of CNTs and Al2O3 NPs at longer milling time exerted higher velocity and attenuation of ultrasonic wave

Carbon nanotubes reinforced aluminum matrix composites – a review of processing techniques

Carbon nanotube reinforced aluminium matrix composites (Al-CNTs) have been widely used in aerospace and automotive industries where high quality and strength is required. The enhanced mechanical properties of Al-CNTs are closely related to processing technique due to challenges within production of these composite materials. In the current review, solid state processing techniques used for synthesizing Al-CNTs have been reviewed to provide an insight into the features and capabilities of each technique regarding the incorporation of CNT reinforcements. To conclude, the mechanical performance of Al-CNT composites is mainly decided by the capability of each technique in the dispersion of CNTs within the aluminum matrix

Microstructural evaluation of ball-milled nano Al2O3 particulate-reinforced aluminum matrix composite powders

A mechanically alloyed mixture of Al-1 wt.% nano-alumina (n-Al2O3) composite powders was produced using a planetary ball milling machine. Different milling times were applied to investigate the effect of milling time on the dispersion and microstructure of n-Al2O3 particulate reinforcement within the aluminum matrix. A good homogeneous dispersion of n-Al2O3 particulates was observed after 8 h of milling. Longer milling times had no significant effect on the dispersion and morphology of n-Al2O3 particulates within the aluminum matrix because a steady state had been reached

Nanomechanical Behavior of Multi-Walled Carbon Nanotubes Particulate Reinforced Aluminum Nanocomposites Prepared by Ball Milling

The nanomechanical properties of carbon nanotubes particulate-reinforced aluminum matrix nanocomposites (Al-CNTs) have been characterized using nanoindentation. Bulk nanocomposite specimens containing 2 wt % multiwalled CNTs (MWCNTs) were synthesized by a combination of ball milling and powder metallurgy route. It has been tried to understand the correlation between microstructural evolution particularly carbon nanotubes (CNTs) dispersion during milling and mechanical properties of Al-2 wt % nanocomposites. Maximum enhancement of +23% and +44% has been found in Young’s modulus and hardness respectively, owing to well homogenous dispersion of CNTs within the aluminum matrix at longer milling time

Reinforcement of aluminum matrix by carbon nano tubes and nano alumina using powder metallurgy method

For the past few years, particulate reinforced aluminum matrix composites (AMCs) have attracted more attention in aerospace, automotive and military industries due to their outstanding mechanical properties including high strength to weight ratio, good wear resistance, good environmental resistance as well as lower costs of production. Besides, AMCs are attractive in engineering applications for weight critical applications which may assist in energy saving along with reduction in the cost. With its low density, aluminum (Al) is a candidate of interest, but further strengthening is needed. The strengthening and development of aluminum has become a critical issue, because only a few materials have been proposed to the industry to strengthen the aluminum matrix. For those proposed materials, fabrication methods and their parameters in order to disperse reinforcements, especially nano reinforcements, within aluminum matrix are still under close scrutiny by researchers all around the world. Because of tangled nature of nano reinforcements, the dispersion of these reinforcements in aluminum matrix is a difficult task and a proper technique to fabricate nano AMCs is needed. In this work, the benefits and limitations of adding Carbon Nano Tubes (CNTs) and Nano Alumina (n-Al2O3) to strengthen the aluminum matrix have been investigated with an emphasis on mechanical milling process and its effects on both nano reinforcement and aluminum matrix. Mechanical milling for different times of 0.5, 2, 5, 8 and 12 h was used to do mechanical alloying of different nano reinforcement contents with aluminum powder. Composite powders were then compacted and sintered at 530 °C. Micro-structural characterization of powders, grain refining analysis through XRD analysis, interfacial bonding assessment through micro structural observation of polished surface of sintered composites, the changes in the density and dimensions of sintered compacts as well as mechanical properties of Al-CNT and Al-Al2O3 composites were measured and compared. Micro structural characterizations showed that, mechanical alloying via ball milling could homogenously disperse CNTs within aluminum matrix. Dispersion uniformity decreased with an increase in the amount of CNTs from 2 wt% up to 5 wt% and 10 wt%. However, further increasing the time of milling caused damage to the CNTs structure and formation of Al4C3 phase. On the other hand, n-Al2O3 dispersed homogenously within aluminum matrix even after adding up high amount of this nano reinforcement to the matrix. Furthermore, mechanical milling offered the advantages of aluminum strengthening through grain refinement and strain hardening. As it was expected for samples fabricated by powder metallurgy processing, nano composite compression and sintering have presented several challenges as it resulted in porous structures, dimension growth and lack of bonding due to the sintering process. Results showed that nano composites which were milled for longer times had higher density after sintering. A minimum densification of 89% was achieved for all specimens. However, attempts to produce dense parts of Al-10CNTs failed due to excessive increase in the dimensions in the presence of CNTs clusters and agglomerations. Micro and nano hardness and Young‘s modulus of Al-CNTs and Al-Al2O3 nano composites as well as compression properties of Al-Al2O3 were measured. Comparison of the results with the previous studies indicated that higher hardness and Young‘s modulus were obtained from the addition of CNTs versus n-Al2O3. On the other hand, in the case of compressive strength of nano composites, an increase in the n-Al2O3 resulted in an increase in compressive stress at break point of 689 MPa, where a homogenous dispersion of nano reinforcement was observed

On the role of molybdenum on the microstructural, mechanical and corrosion properties of the GTAW AISI 316 stainless steel welds

A comparative study was carried out on GTAW AISI 316 welds fabricated by three different filler metals including ER-317M, ER-316 and ER-308. Filler metals were selected in a way to induce varying Molybdenum (Mo) concentrations in the weld metal, so that the effect of Mo on the microstructural, mechanical and corrosion behavior of the welds was investigated. Microstructural studies revealed that as Mo concentration increased in the weld metal, the dendritic morphology of this zone gradually was changed from cellular dendritic to columnar dendritic and a noticeable amount of austenitic phase and precipitations were formed. Mo-containing ER-316 and ER-317M welds showed appreciable amount of Mo- and Cr-rich carbides such as (Fe,Cr)23C6 which formed at the grain boundaries of δ-ferrite phase resulting in increased the hardness and strength of welded samples. The highest microhardness value of 188 HV and yield strength of 330 MPa belonged to ER-317M welds containing the highest Mo concentration. Also, corrosion resistance of the welds significantly improved by increasing Mo concentration and a minimum corrosion rate of 4.178 mm/year was accounted for ER-317M welds in which, the formation of passive film was more facilitated due to the higher concentration of Mo