Plasma And Cold Sprayed Aluminum Carbon Nanotube Composites: Quantification Of Nanotube Distribution And Multi-Scale Mechanical Properties

Carbon nanotubes (CNT) could serve as potential reinforcement for metal matrix composites for improved mechanical properties. However dispersion of carbon nanotubes (CNT) in the matrix has been a longstanding problem, since they tend to form clusters to minimize their surface area. The aim of this study was to use plasma and cold spraying techniques to synthesize CNT reinforced aluminum composite with improved dispersion and to quantify the degree of CNT dispersion as it influences the mechanical properties. Novel method of spray drying was used to disperse CNTs in Al-12 wt.% Si pre-alloyed powder, which was used as feedstock for plasma and cold spraying. A new method for quantification of CNT distribution was developed. Two parameters for CNT dispersion quantification, namely Dispersion parameter (DP) and Clustering Parameter (CP) have been proposed based on the image analysis and distance between the centers of CNTs. Nanomechanical properties were correlated with the dispersion of CNTs in the microstructure. Coating microstructure evolution has been discussed in terms of splat formation, deformation and damage of CNTs and CNT/matrix interface. Effect of Si and CNT content on the reaction at CNT/matrix interface was thermodynamically and kinetically studied. A pseudo phase diagram was computed which predicts the interfacial carbide for reaction between CNT and Al-Si alloy at processing temperature. Kinetic aspects showed that Al4C3 forms with Al-12 wt.% Si alloy while SiC forms with Al-23wt.% Si alloy. Mechanical properties at nano, micro and macro-scale were evaluated using nanoindentation and nanoscratch, microindentation and bulk tensile testing respectively. Nano and micro-scale mechanical properties (elastic modulus, hardness and yield strength) displayed improvement whereas macro-scale mechanical properties were poor. The inversion of the mechanical properties at different scale length was attributed to the porosity, CNT clustering, CNT-splat adhesion and Al4C3 formation at the CNT/matrix interface. The Dispersion parameter (DP) was more sensitive than Clustering parameter (CP) in measuring degree of CNT distribution in the matrix

The global burden of cancer attributable to risk factors, 2010-19 : a systematic analysis for the Global Burden of Disease Study 2019

Background Understanding the magnitude of cancer burden attributable to potentially modifiable risk factors is crucial for development of effective prevention and mitigation strategies. We analysed results from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 to inform cancer control planning efforts globally. Methods The GBD 2019 comparative risk assessment framework was used to estimate cancer burden attributable to behavioural, environmental and occupational, and metabolic risk factors. A total of 82 risk-outcome pairs were included on the basis of the World Cancer Research Fund criteria. Estimated cancer deaths and disability-adjusted life-years (DALYs) in 2019 and change in these measures between 2010 and 2019 are presented. Findings Globally, in 2019, the risk factors included in this analysis accounted for 4.45 million (95% uncertainty interval 4.01-4.94) deaths and 105 million (95.0-116) DALYs for both sexes combined, representing 44.4% (41.3-48.4) of all cancer deaths and 42.0% (39.1-45.6) of all DALYs. There were 2.88 million (2.60-3.18) risk-attributable cancer deaths in males (50.6% [47.8-54.1] of all male cancer deaths) and 1.58 million (1.36-1.84) risk-attributable cancer deaths in females (36.3% [32.5-41.3] of all female cancer deaths). The leading risk factors at the most detailed level globally for risk-attributable cancer deaths and DALYs in 2019 for both sexes combined were smoking, followed by alcohol use and high BMI. Risk-attributable cancer burden varied by world region and Socio-demographic Index (SDI), with smoking, unsafe sex, and alcohol use being the three leading risk factors for risk-attributable cancer DALYs in low SDI locations in 2019, whereas DALYs in high SDI locations mirrored the top three global risk factor rankings. From 2010 to 2019, global risk-attributable cancer deaths increased by 20.4% (12.6-28.4) and DALYs by 16.8% (8.8-25.0), with the greatest percentage increase in metabolic risks (34.7% [27.9-42.8] and 33.3% [25.8-42.0]). Interpretation The leading risk factors contributing to global cancer burden in 2019 were behavioural, whereas metabolic risk factors saw the largest increases between 2010 and 2019. Reducing exposure to these modifiable risk factors would decrease cancer mortality and DALY rates worldwide, and policies should be tailored appropriately to local cancer risk factor burden. Copyright (C) 2022 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license.Peer reviewe

Aluminum Composite Reinforced With Multiwalled Carbon Nanotubes From Plasma Spraying Of Spray Dried Powders

Homogenous dispersion of carbon nanotubes (CNTs) in micron sized aluminum silicon alloy powders was achieved by spray drying. Excellent flowability of the powders allowed fabrication of thick composite coatings and hollow cylinders (5 mm thick) containing 5 wt.% and 10 wt.% CNT by plasma spraying. Two phase microstructure with matrix having good distribution of CNT and CNT rich clusters was observed. Microstructural evolution has been explained using single splat and the infiltration of CNT clusters by liquid metal. Partial CNT surface damage was observed in case of the 10 wt.% CNT coating due to CNT mesh formation and smaller size of spray dried agglomerate. Increase in the elastic modulus and improvement in the yield strength and elastic recovery properties due to CNT addition was observed by nanoindentation. © 2008 Elsevier B.V. All rights reserved

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

Interface In Carbon Nanotube Reinforced Aluminum Silicon Composites: Thermodynamic Analysis And Experimental Verification

Interface in carbon nanotubes (CNTs) reinforced aluminium-silicon composites are studied via thermodynamic and kinetic analysis. A pseudo-phase diagram has been generated based on the thermodynamic calculations to predict the type of carbide (Al4C3 or SiC) that would form at the matrix-CNT interface as a function of matrix composition and processing temperature. The pseudo-phase diagram is useful in high temperature processes like thermal spray forming. Critical thickness values for carbide nucleation suggest the formation of Al4C3 with Al-11.6 wt.% Si alloy and SiC with Al-23 wt.% Si alloy. Thermodynamic calculations show that the amount of Al4C3 increases with an increase in the CNT content. The computed results perfectly agree with the results obtained by XRD, SEM of fracture surface and high-resolution transmission electron microscopy (HRTEM) observations on Al-11.6 wt.% Si and Al-23 wt.% Si alloy reinforced with CNT. © 2009 Elsevier B.V. All rights reserved

Structural Transformations In Carbon Nanotubes During Thermal Spray Processing

This study compares the interaction of carbon nanotubes (CNTs) with the flame/energy sources during different thermal spray processes viz. plasma spraying (PS), high-velocity oxy fuel spraying (HVOF), cold spraying (CS), and plasma spraying of liquid precursor (PSLP). CNTs were successfully retained as reinforcement in metal and ceramic composite coatings in all thermal spray processes except PSLP. The retention of CNT structure is attributed to micron size metal/ceramic powder which acts as a carrier and thermal shield against high heat in plasma spraying (PS) and high-velocity oxy fuel spraying (HVOF). However, vaporization of CNTs occurred in PSLP under the intense heat of the plasma which is attributed to phase transformation in unshielded CNTs. © 2009 Elsevier B.V. All rights reserved

Effect of Sc Addition on the Microstructure and Wear Properties of A356 Alloy and A356–TiB2in Situ Composite

In this study, the effect of Sc addition on the grain refinement, modification of the eutectic Si, mechanical and wear properties of A356 and A356–10 wt% TiB2in situ composite has been investigated. The A356–10 wt% TiB2 composites were prepared by an in situ reaction between K2TiF6 and KBF4 salts, which are added in proper stoichiometric ratio to form TiB2 in the A356 alloy melt at a temperature of 1073 K (800 °C). Al–2 wt% Sc master alloy was added to A356 and A356–10 wt% TiB2 melt to introduce 0.2 and 0.4 wt% Sc in the alloy and the composite. Addition of Sc reduced the secondary dendrite arms spacing (SDAS) by 50% and changed the Si morphology from needle-like to fine spheroidal particles. Microstructure of Sc modified alloys which were cast for different holding times of 0, 30, 60 and 120 min indicated that there was no fading or poisoning effect on the SDAS and eutectic Si morphology. Hardness was found to increase due to addition of Sc and TiB2. Pin-on-disk wear tests indicated that Sc addition increase the wear resistance of A356 alloy but reduced the wear resistance of A356–TiB2 composite

Spark plasma sintered tantalum carbide: Effect of pressure and nano-boron carbide addition on microstructure and mechanical properties

TaC and TaC-1 wt.% B(4)C powders were consolidated using spark plasma sintering (SPS) at 1850 degrees C and varying pressure of 100, 255 and 363 MPa. The effect of pressure on the densification and grain size is evaluated. The role of nano-sized B(4)C as sintering aid and grain growth inhibitor is studied by means of XRD, SEM and high resolution TEM. Fully dense TaC samples were produced at a pressure of 255 MPa and higher at 1850 degrees C. The increasing pressure also resulted in an increase in TaC grain size. Addition of B(4)C leads to an increase in the density of 100 MPa sample from 89% to 97%. B(4)C nano-powder resists grain growth even at high pressure of 363 MPa. The formation of TaB(2)/Carbon at TaC grain boundaries helps in pinning the grain boundary and inhibiting grain growth. The effect of B(4)C addition on hardness and elastic modulus measured by nanoindentation and the indentation fracture toughness has been studied. Relative fracture toughness increased by up to 93% on B(4)C addition

Effect of Sc addition on the microstructure and wear properties of A356 alloy and A356–TiB₂ in situ composite

In this study, the effect of Sc addition on the grain refinement, modification of the eutectic Si, mechanical and wear properties of A356 and A356–10 wt% TiB2 in situ composite has been investigated. The A356–10 wt% TiB2 composites were prepared by an in situ reaction between K2TiF6 and KBF4 salts, which are added in proper stoichiometric ratio to form TiB2 in the A356 alloy melt at a temperature of 1073 K (800°C). Al–2 wt% Sc master alloy was added to A356 and A356–10 wt% TiB2 melt to introduce 0.2 and 0.4 wt% Sc in the alloy and the composite. Addition of Sc reduced the Secondary Dendrite Arms Spacing (SDAS) by 50% and changed the Si morphology from needle-like to fine spheroidal particles. Microstructure of Sc modified alloys which were cast for different holding times of 0, 30, 60 and 120 min indicated that there was no fading or poisoning effect on the SDAS and eutectic Si morphology. Hardness was found to increase due to addition of Sc and TiB2. Pin-on-disk wear tests indicated that Sc addition increase the wear resistance of A356 alloy but reduced the wear resistance of A356–TiB2 composite

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

<p>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.</p