Srinivasa R. Bakshi

Carbon nanotube reinforced metal matrix composites - a review

Abstract This review summarises the research work carried out in the field of carbon nanotube (CNT) metal matrix composites (MMCs). Much research has been undertaken in utilising CNTs as reinforcement for composite material. However, CNT-reinforced MMCs have received the least attention. These composites are being projected for use in structural applications for their high specific strength as well as functional materials for their exciting thermal and electrical characteristics. The present review focuses on the critical issues of CNT-reinforced MMCs that include processing techniques, nanotube dispersion, interface, strengthening mechanisms and mechanical properties. Processing techniques used for synthesis of the composites have been critically reviewed with an objective to achieve homogeneous distribution of carbon nanotubes in the matrix. The mechanical property improvements achieved by addition of CNTs in various metal matrix systems are summarised. The factors determining strengthening achieved by CNT reinforcement are elucidated as are the structural and chemical stability of CNTs in different metal matrixes and the importance of the CNT/metal interface has been reviewed. The importance of CNT dispersion and its quantification is highlighted. Carbon nanotube reinforced MMCs as functional materials are summarised. Future work that needs attention is addressed.

Boron nitride nanotube reinforced polylactide-polycaprolactone copolymer composite: mechanical properties and cytocompatibility with osteoblasts and macrophages in vitro.

Biodegradable polylactide-polycaprolactone copolymer (PLC) has been reinforced with 0, 2 and 5wt.% boron nitride nanotubes (BNNTs) for orthopedic scaffold application. Elastic modulus of the PLC-5wt.% BNNT composite, evaluated through nanoindentation technique, shows a 1370% increase. The same amount of BNNT addition to PLC enhances the tensile strength by 109%, without any adverse effect on the ductility up to 240% elongation. Interactions of the osteoblasts and macrophages with bare BNNTs prove them to be non-cytotoxic. PLC-BNNT composites displayed increased osteoblast cell viability as compared to the PLC matrix. The addition of BNNTs also resulted in an increase in the expression levels of the Runx2 gene, the main regulator of osteoblast differentiation. These results indicate that BNNT is a potential reinforcement for composites for orthopedic applications.

Carbon Nanotubes : Reinforced Metal Matrix Composites

Introduction Composite Materials Development of Carbon Fibers Carbon Nanotubes: Synthesis and Properties Carbon Nanotube-Metal Matrix Composites Chapter Highlights Processing Techniques Powder Metallurgy Routes Melt Processing Thermal Spraying Electrochemical Routes Novel Techniques Characterization of Metal Matrix-Carbon Nanotube Composites X-Ray Diffraction Raman Spectroscopy Scanning Electron Microscopy with Energy Dispersive Spectroscopy High Resolution Transmission Electron Microscopy Electron Energy Loss Spectroscopy X-Ray Photoelectron Spectroscopy Mechanical Properties Evaluation Thermal Properties Electrical Properties Electrochemical Properties Metal-Carbon Nanotube Systems Aluminum-Carbon Nanotube System Copper-Carbon Nanotube System Nickel-Carbon Nanotube System Magnesium-Carbon Nanotube System Other Metals-Carbon Nanotube Systems Mechanics of Metal-Carbon Nanotube Systems Elastic Modulus of Metal Matrix-Carbon Nanotube Composites Strengthening Mechanisms in Metal Matrix-Carbon Nanotube Composites Interfacial Phenomena in Carbon Nanotube Reinforced Metal Matrix Composites Significance of Interfacial Phenomena Energetics of Carbon Nanotube-Metal Interaction Carbon Nanotube-Metal Interaction in Various Systems Dispersion of Carbon Nanotubes in Metal Matrix Significance of Carbon Nanotube Dispersion Methods of Improving Carbon Nanotube Dispersion Quantification of Carbon Nanotube Dispersion Electrical, Thermal, Chemical, Hydrogen Storage, and Tribological Properties Electrical Properties Thermal Properties Corrosion Properties Hydrogen Storage Property Sensors and Catalytic Properties Tribological Properties Computational Studies in Metal Matrix-Carbon Nanotube Composites Thermodynamic Prediction of Carbon Nanotube-Metal Interface Microstructure Simulation Mechanical and Thermal Property Prediction by the Object-Oriented Finite Element Method Summary and Future Directions Summary of Research on MM-CNT Composites Future Directions

Aluminum-Based Cast In Situ Composites: A Review

In situ composites are a class of composite materials in which the reinforcement is formed within the matrix by reaction during the processing. In situ method of composite synthesis has been widely followed by researchers because of several advantages over conventional stir casting such as fine particle size, clean interface, and good wettability of the reinforcement with the matrix and homogeneous distribution of the reinforcement compared to other processes. Besides this, in situ processing of composites by casting route is also economical and amenable for large scale production as compared to other methods such as powder metallurgy and spray forming. Commonly used reinforcements for Al and its alloys which can be produced in situ are Al2O3, AlN, TiB2, TiC, ZrB2, and Mg2Si. The aim of this paper is to review the current research and development in aluminum-based in situ composites by casting route.

Nanomechanical behaviour of plasma sprayed PZT coatings

Abstract Nanomechanical properties of the plasma sprayed lead zirconate titanate (PZT) coating have been investigated using nanoindentation technique. PZT coating processed at higher plasma power of 32 kW exhibited lower elastic modulus E of 98 GPa compared with the modulus (113 GPa) of the coating processed at plasma power of 20 kW. The variation in the elastic modulus is attributed to the fine porosity of the PZT coating, which is formed during plasma spraying. Porosity increases by evaporation of PbO phase during plasma spraying. Overall effective elastic modulus of both coatings is computed using micromechanics models and compared with the experimentally obtained values. Hashin–Shtrikman and rule of mixtures models predict values that closely match with nanoindentation values.

Ab-initio molecular modeling of interfaces in tantalum-carbon system

Processing of ultrahigh temperature TaC ceramic material with sintering additives of B4C and reinforcement of carbon nanotubes (CNTs) gives rise to possible formation of several interfaces (Ta2C-TaC, TaC-CNT, Ta2C-CNT, TaB2-TaC, and TaB2-CNT) that could influence the resultant properties. Current work focuses on interfaces developed during spark plasma sintering of TaC-system and performing ab initio molecular modeling of the interfaces generated during processing of TaC-B4C and TaC-CNT composites. The energy of the various interfaces has been evaluated and compared with TaC-Ta2C interface. The iso-surface electronic contours are extracted from the calculations eliciting the enhanced stability of TaC-CNT interface by 72.2%. CNTs form stable interfaces with Ta2C and TaB2 phases with a reduction in the energy by 35.8% and 40.4%, respectively. The computed Ta-C-B interfaces are also compared with experimentally observed interfaces in high resolution TEM images.

Intersplat Friction Force and Splat Sliding in a Plasma-Sprayed Aluminum Alloy Coating during Nanoindentation and Microindentation

This study computes the friction force during splat sliding in the plasma-sprayed Al-Si coating based on the instrumented depth-sensing nanoindentation and microindentation experiments. A small intersplat friction force (approximately 10(-4) N) contributes to the occurrence of the splat sliding. As compared with nanoindentation, more and more splat sliding occurs during microindentation because of the increase in the applied load, which accounts for the approximately 26% loss of the elastic modulus.

Densification mechanisms during reactive spark plasma sintering of Titanium diboride and Zirconium diboride

Abstract In this study, dense fine-grained ZrB2 and TiB2 were fabricated using reactive spark plasma sintering (RSPS) of ball-milled Zr/B and Ti/B mixtures. Systematic investigations were carried out to understand the mechanisms of reactive sintering. Two densification mechanisms were found to be operating during RSPS. The first stage of densification was due to self-propagating high temperature synthesis reaction leading to formation of ZrB2 and TiB2 compacts having relative density of ~48 and ~65%, respectively. The second stage of densification occurred at temperatures more than 1100 °C and resulted in final relative density of more than 98%. Electron backscatter diffraction and electron microscopy studies on interrupted RSPS samples as well as dense samples showed deformed grains and presence of slip steps while grain orientation spread map and pole figure analysis confirmed plastic flow. Plastic flow-aided pore closure is shown as major mechanism during reactive sintering.

Effect of carrier gas on mechanical properties and fracture behaviour of cold sprayed aluminium coatings

Abstract Two different coatings of 1100 aluminium were cold sprayed onto similar substrates, using He and He–20N2 (vol.-%) mixture as carrier gases. Three point bend testing was carried out. The elastic moduli of the coatings were found to be close to each other and the substrate. The He processed coating showed higher fracture strength which was attributed to the higher degree of strain hardening. The He–20N2 processed coating failed at lower stress owing to its strain relaxed structure. The mode 1 fracture of the coating substrate system was found to be higher for the helium processed coating. The toughness was correlated to the microstructure. The delaminated coating showed a higher degree of brittle failure of the interface for the He processed coating.

Spark Plasma Sintering Process as a Tool for Achieving Microstructural Integrity

The fact that real materials are not perfect crystals, is critical to materials engineering as the presence of crystalline defects is the most important feature of the microstructure which influences the mechanical properties. Exposure of materials to high temperature for long duration would result in structural failure, when a sub-size crack grows into a critical level. This paper concentrates on the novel application of spark plasma sintering (SPS) technique in achieving microstructural integrity of materials by crack closure using the superior capability of SPS for annealing the defects in materials. Due to the presence of applied compressive stress, expansion is restricted and brings about the closure of cracks. The crack surfaces then come in contact with each other, and energization between the crack surfaces causes them to bond. The presentation would bring about the nature of bonding achieved through SPS when two model systems, diffusion bonding of stainless steel discs and stainless steel with ferroboron powder, were considered and highlighted its applicability through systematic optimization.