Of late, nanotechnology seems to be rapidly thrusting its applications in all aspects of life including engineering and medicine. Materials science and engineering has experienced a tremendous growth in the field of nanocomposite development with enhanced chemical, mechanical, and physical properties. A wide array of research has been conducted in the processing of nanocomposites. Consolidation of these systems from loose particles to bulk free form entities has always been a challenge. To name a few, traditional consolidation techniques such as cold pressing and sintering at high temperatures, hot pressing, and hot isostatic pressing have strong limitations of not being able to retain the nanoscale grain size due to the excessive grain growth during processing. This article reviews in detail the results from numerous studies on various methods for manufacturing nanocomposites with improved properties and retained nanostructures. Both challenges and recent advances are discussed in detail in this review.

Challenges and advances in nanocomposite processing techniques

Carbon nanotube (CNT) reinforced magnesium was synthesized using the powder metallurgy technique followed by hot extrusion. Up to 0.3 wt% of CNTs were added as reinforcements. The effects of the carbon nanotubes on the physical and mechanical properties of Mg were investigated. The thermo-mechanical property results show an increase in thermal stability with increasing amount of CNTs in the Mg nanocomposites. Mechanical property characterizations reveal an improvement of yield strength, ductility and work of fracture with higher weight percentages of CNTs incorporated. An attempt is made to correlate the physical and mechanical properties with the increasing weight fractions of carbon nanotubes in the pure Mg matrix.

https://iopscience.iop.org/article/10.1088/0957-4484/17/1/002/pdf

Development of novel carbon nanotube reinforced magnesium nanocomposites using the powder metallurgy technique

In the present study, magnesium based composites with three different volume percentages of nano-sized Al2O3 particulates reinforcement were fabricated using blend-press-sinter methodology avoiding ball milling. Microstructural characterization of the materials revealed reasonably uniform distribution of nano-size Al2O3 reinforcement and presence of minimal porosity. Mechanical properties characterization revealed that the presence of nano-Al2O3 particulates as reinforcement lead to a simultaneous increase in hardness, elastic modulus, 0.2% yield strength, UTS and ductility of pure magnesium. The results revealed that the 0.2% yield strength, UTS and ductility combination of the magnesium nano-composites containing 0.66 and 1.11 vol% of alumina remained higher when compared to high strength magnesium alloy AZ91 reinforced with much higher amount of micrometer size SiC particulates. An attempt is made in the present study to correlate the effect of presence of nano-Al2O3 as reinforcement and its increasing amount with the microstructural and mechanical properties of magnesium.

Development of high performance magnesium nano-composites using nano-Al2O3 as reinforcement

Elemental Mg and Mg-alloy (AZ91D) based composites reinforced with 15 vol.% silicon carbide (SiC) particulates (average particle size 15 μm and 150 μm) were synthesised by stir casting technique. Particle distribution, particle–matrix interfacial reaction, hardness and mechanical properties in the as cast as well as T4 heat-treated conditions were investigated. The composite materials show uniform distribution of SiC particulates. The average grain size decreases with the presence of SiC particulates and the grain size further decreases as the particle size decreases. The AZ91D alloy composite shows an increase in hardness and elastic modulus compared to monolithic alloys. The improvement in elastic modulus of composite containing 15 μm size SiC particles is significantly higher than the composite with 150 μm size particles. The ultimate tensile strength and ductility of composite materials were reduced compared to unreinforced alloy.

Processing and mechanical properties of SiC reinforced cast magnesium matrix composites by stir casting process

The disintegrated melt deposition method was used to fabricate Mg nanocomposites containing 0.3, 1.3, 1.6 and 2 wt.% carbon nanotubes (CNTs). The nanocomposites obtained were hot extruded and characterized for their physical and mechanical properties. Lighter nanocomposites have been produced with the incorporation of CNTs than without them. A simultaneous increase in 0.2% yield strength, ultimate tensile strength and ductility was found for the Mg–CNT nanocomposites, until a threshold of 1.3 wt.% was reached.

Simultaneous enhancement in strength and ductility by reinforcing magnesium with carbon nanotubes

In the present study, elemental and silicon carbide reinforced magnesium materials were synthesized using an innovative disintegrated melt deposition method followed by hot extrusion. Microstructural characterization studies revealed the presence of minimal porosity and completely recrystallized matrix in all the unreinforced and reinforced samples. In the case of reinforced magnesium samples, a fairly uniform distribution of SiC particulates and good SiC-Mg interfacial integrity was realized. The results of microhardness measurements revealed an increase in the brittleness of the SiC-Mg interfacial region with an increase in the amount of SiC particulates. Results of physical and mechanical properties characterization revealed that the increasing presence of SiC particulates led to an increase in hardness and elastic modulus, does not affect 0.2% yield strength and reduces the ultimate tensile strength, ductility, work for fracture and coefficient of thermal expansion. An attempt is made to correlate the results of physical and mechanical properties testing with that of the microstructural characterization.

Synthesis, microstructure and properties characterization of disintegrated melt deposited Mg/SiC composites

The aim of the present study was to determine the elastic modulus of magnesium based composites containing different volume fractions of SiC particulate using an innovative suspended beam type impact based technique. This applies classical vibration theory, which relates the resonant frequency of the test specimens to the geometry and material properties of the metal matrix composites. The elastic modulus values were determined from the funda mental resonant frequency obtained from the experiment and density measurements. In addition, a finite element model was proposed for determining the dynamic elastic modulus of MMCs with different SiC reinforcement content using the first natural frequency corresponding to the flexural mode. The elastic modulus values obtained from the finite element model were in close agreement with the values obtained from the impact based experiments and in better agreement than those from theoretical methods such as the shear lag, Eshelby, and Halpin–Tsai models.

Modelling and determination of dynamic elastic modulus of magnesium based metal matrix composites

An understanding of the work hardening behaviour of particulate reinforced metal matrix composites is crucial in optimising the parameters for deformation processing of these materials. In the present study, SiC reinforced magnesium metal matrix composites were produced using a liquid phase process. The microstructure of the composite was characterised and the mechanical properties were determined. The results of the ambient temperature tensile testing on the extruded Mg and Mg/SiC specimens revealed that an increase in the weight percentage of SiC particulates in pure magnesium increases the elastic modulus, does not affect the 0·2% yield strength, and reduces the ultimate tensile strength and ductility. A modified continuum model was applied to relate the work hardening behaviour of the composites to microstructural parameters and to predict the fracture strain of the composites. The model is shown to predict the fracture strain of the composites quite accurately for all the three weight fractio...

Application of model for work hardening behaviour of SiC reinforced magnesium based metal matrix composites

The objective of the present work was to investigate the effect of presence of SiC reinforcement and the vibration frequency on the overall damping characteristics of pure magnesium. The testing method uses a combination of the modified free – free beam method coupled with a circle fit approach. The effect of frequency on the damping property was studied by adding end masses to the specimen so as to alter the resonant frequency of the suspended beam. In the present study, the results are compared against a monolithic magnesium sample. The results revealed a higher damping capability of the composite specimen at all tested frequencies when compared to monolithic magnesium. Both monolithic and reinforced magnesium showed a progressive decrease in damping with an increase in frequency. An attempt is made to rationalise the damping behaviour of the composite in terms of the presence of a process induced plastic zone at the matrix/particulate interface and the operating frequency.

D. Saravanaranganathan

Papers

Synthesis, microstructure and properties characterization of disintegrated melt deposited Mg/SiC composites

Modelling and determination of dynamic elastic modulus of magnesium based metal matrix composites

Application of model for work hardening behaviour of SiC reinforced magnesium based metal matrix composites

Effect of presence of SiC and operating frequency on the damping behaviour of pure magnesium