M. F. A. Goosen

Structure Property Relationship of Suspension Thermally Sprayed WC-Co Nanocomposite Coatings

Tribomechanical properties of nanostructured coatings deposited by suspension high velocity oxy-fuel (S-HVOF) and conventional HVOF (Jet Kote) spraying were evaluated. Nanostructured S-HVOF coatings were obtained via ball milling of the agglomerated and sintered WC-12Co feedstock powder, which were deposited via an aqueous-based suspension using modified HVOF (TopGun) process. Microstructural evaluations of these hardmetal coatings included transmission electron microscopy, x-ray diffraction, and scanning electron microscopy equipped with energy dispersive x-ray spectroscopy. The nanohardness and modulus of the coated specimens were investigated using a diamond Berkovich nanoindenter. Sliding wear tests were conducted using a ball-on-flat test rig. Results indicated that low porosity coatings with nanostructured features were obtained. High carbon loss was observed, but coatings showed a high hardness up to 1000 HV2.9N. S-HVOF coatings also showed improved sliding wear and friction behavior, which were attributed to nanosized particles reducing ball wear in three-body abrasion and support of metal matrix due to uniform distribution of nanoparticles in the coating microstructure.

Influence of post-treatment on the microstructural and tribomechanical properties of suspension thermally sprayed WC-12 wt%Co nanocomposite coatings.

The potential to improve the tribomechanical performance of HVOF-sprayed WC–12Co coatings was studied by using aqueous WC–12Co suspensions as feedstock. Both as-sprayed and hot-isostatic-pressed (HIPed) coatings were studied. Mathematical models of wear rate based on the structure property relationships, even for the conventionally sprayed WC–Co hardmetal coatings, are at best based on the semiempirical approach. This paper aims to develop these semiempirical mathematical models for suspension sprayed nanocomposite coatings in as-sprayed and heat-treated (HIPed) conditions. Microstructural evaluations included transmission electron microscopy, X-ray diffraction and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. The nanohardness and modulus of the coated specimens were investigated using a diamond Berkovich nanoindenter. Sliding wear tests were conducted using a ball-on-flat test rig. Results indicated that the HIPing post-treatment resulted in crystallization of amorphous coating phases and increase in elastic modulus and hardness. Influence of these changes in the wear mechanisms and wear rate is discussed. Results are also compared with conventionally sprayed high-velocity oxy-fuel hardmetal WC–Co coatings.

Finite Element Modeling of Sliding Wear in a Composite Alloy Using a Free-Mesh

A finite element analysis (FEA) based wear algorithm model is presented to predict sliding wear behavior of a composite cobalt-based (Stellite 6) alloy. This study aims to provide an understanding of FEA model behavior using: (a) free-mesh, (b) composite material microstructure, and (c) wear test conditions of loading and geometry which are consistent with ASTM G133-02. Results indicate that the wear model using free-mesh is able to predict wear in composite alloy within the limits of experimental deviation using a suitable kD (wear-rate) value. The rationale for the differences in the experimental setup and FEA model calculations is discussed in terms of the role of wear debris, wear mechanisms, and ball wear.

Suspension thermal sprayed nanocomposite WC-Co coatings: Nano-indentation assessment

T critical challenge of current nanoscale oxide super thermal insulation materials, such as SiO2 and Al2O3 nano-particle aggregates and their composites, is the critical trade-off between extremely low thermal conductivity and unsatisfied thermal stability (nanostability typically below 1100oC). It is crucially important to modify current materials and further discover novel candidates which could balance the two key properties. This presentation shows progresses on optimal thermal stability of modified Al2O3 nano-particle aggregate; and in addition, new candidates of super thermal insulation materials, such as nano-Si3N4 and nanoSiC, which are commonly believed as excellent heat conductors. Especially, the new nano-systems exhibited good nanostability up to 1500°C. The striking results incorporated superior sintering stability of structural ceramics as SiC and Si3N4 with multiple phonon scattering mechanisms in nano-materials. It is possible to put forward this novel concept to design and search new types of high temperature thermal insulation materials through nano-scale morphology engineering of structural ceramics with excellent thermal stability, regardless their high intrinsic lattice thermal conductivities.Deok-Won Lee is an Oral and Maxillofacial Surgery Specialist and Associate Professor of Kyung Hee University College of Dentistry. His expertise is in treating and improving the oral and maxillofacial health and wellbeing of people. His research on dental implant materials creates new pathways for improving healthcare. He is continually building and investigating on adequate material for implantation through in-vivo and in-vitro models based on years of experience in research, evaluation, teaching and administration both in hospital and education institutions.Statement of the Problem: Nanoindentation of WC-12Co thermal spray coatings has been used to evaluate the elastic modulus and hardness of coating on the polished surface of the coatings. While there has been much progress overall, limited research has been reported on the deposition and evaluation of WC-cermet coatings. The aim of this study was to evaluate the microstructural and nanohardness characteristics of tungsten carbide-cobalt (WC-Co) cermet coatings deposited by liquid suspension spraying.Statement of the Problem: A more ubiquitous application of Ti-6Al-4V in the aerospace industry has been hindered by its poor set of surface properties. The cold spray coating (CSC) process is suitable for improvements in the surface properties but the process is very complex, and highly dependent and sensitive to small changes in its many process parameters. Moreover, the CSC is also very selective of the choice of powder materials. The choice is not only based on application requirements but also on plastic deformability of the powder.W developed an optically controllable organic field transistor (OFET) by employing photochromic diarylethene (DAE) molecules as a transistor channel layer. DAE molecules are known to undergo photochromic reaction, i.e., reversible conformational change between closedand open-ring isomers by alternating ultraviolet (UV) and visible (VIS) light irradiation. We found that the drain current in the DAE-based OFET also showed reversible change accompanied by this conformational change; the closed-ring isomer produced by UV light exhibited a transistor operation under appropriate gate and drain bias voltages, meanwhile the open-ring isomer produced by VIS light showed no drain current. As a result, a remarkably high on/off ratio of 1,000 was achieved. The drain current modulation can be attributed to the drastic transformation in the π-conjugation system in association with the photo-isomerization. These results present two important messages. The first one is that this compound has dual properties: organic semiconductor and photochromism. The second is that a phase transition between semiconductor and insulator can be induced by light irradiation. Based on these achievements, we demonstrate laser drawing of one-dimensional (1D) channels on an OFET with a photochromic DAE layer. The main findings are: i) a number of 1D channels can be written and erased repeatedly in the DAE layer by scanning UV and VIS focused laser spots alternately between the source and drain electrodes, ii) the conductivity of the 1D channel can be controlled by the illumination conditions, and iii) it is possible to draw an analogue adder circuit by optically writing 1D channels so as to overlap a portion of the channels and perform optical summing operations by local laser illumination on the respective channels. These findings will open new possibilities of various optically reconfigurable low-dimensional organic transistor circuits, which are not possible with conventional thin film OFETs.G nanoparticles of different shape and size have been designed and applied as contrast-enhancing agents for various imaging techniques: optical coherence tomography, fluorescence imaging, optical microscopy, photoacoustic imaging and sensing; and recently, for experimental cancer therapy as enhancers of thermal and radiation modes. In this presentation, we are focusing on different sides of gold nanorods (GNRs) applications, as well as their synthesis, functionalization, and specific targeting. The role of GNRs in comprehensive cancer diagnostics and treatment was analyzed and created the novel GNRs’ modifications of wide-ranging aspects ratio, size with high yield and quality. The GNRs were assessed by their toxicity for altered categories, such as amount of gold, surface area, optical density of their solutions and number of particles. GNRs have been reviewed as contrast agents with near-infrared absorption as highly efficient transformers of light energy into heat. Here, we present the use of GNRs as plasmonic nanoparticles for selective photothermal therapy of human acute and chronicle leukemia cells using a near-infrared laser. We have investigated GNRs as potential enhancers of radiotherapy. We have demonstrated high impact of external surface chemistry, role of molecules size and thickness of surfactant layer for damage of cancer cells by electromagnetic radiation. GNRs were evaluated as theranostic agents for imaging, photothermal and radiation modalities. The results may impact pre-clinical GNRs’ applications, molecular imaging, and quantitative sensing of biological analytes.W have done much work about silicon (Si) in solar cells and lithium ion batteries (LIBs). In the aspect of solar cell, we used silver (Ag)-assisted chemical etching method to fabricate black silicon solar cells with efficiency over 18% in 2013 and large-scale production was carried out. Besides, nickel, which is cheaper than Ag, was used as assisted metal to fabricate black silicon structure for the first time and surface reflectance of 1.59% was obtained. In the aspect of LIBs, we used Si powders made from broken Si wafers with different electrical resistivity in semiconductor industry as anode material in LIBs. We found that Si powders made from Si wafers with lower electrical resistivity show better electrochemical performance (higher capacity, and better rate performance) in LIBs. Therefore, broken Si wafers in semiconductor industry should be classified according to their electrical resistivity, which can be convenient for being used as anode raw materials for LIBs.Introduction: Si clathrate compounds have been widely studied due to their unique open-framework structures of Si polyhedrons. Two types of Si clathrates encapsulating Na atoms have been known: type I (Na8Si46) and type II (NaxSi136, 0 < x ≤ 24). These Na-Si clathrates have been generally synthesized by thermal decomposition of a Na-Si binary compound, Na4Si4, at 673–823 K under high-vacuum conditions (< 10−2 Pa), and the obtained samples were in the form of powder with a particle size in the micrometer range.I cold forming, die materials are subjected to severe wear because of high contact temperature and pressure. D2 steel is used as die material for cold forming applications. However, its friction and wear properties have not been studied fully under high stress and high temperature conditions. Friction and wear behavior of D2 steel against AISI 52100 and Alumina have been studied under dry sliding conditions in temperature range of RT – 150°C, using ball-on-disc universal tribometer. For sliding distance test the wear rate of D2 with AISI 52100 is less than the Alumina for entire range at 150°C. The wear volume of D2 steel increases with the increase in sliding distance from 200 m to 1000 m against AISI 52100 and Alumina. For D2 steel, highest coefficient of friction (μ) 0.751 and 0.754 against AISI 52100 and Alumina was obtained at 5 N, whereas minimum μ of 0.32 and 0.43 against AISI 52100 and Alumina was obtained at 25 N, these tests were carried out at 150°C. For temperature test, highest coefficient of friction (μ) of 0.92 and 0.7671 against AISI 52100 and Alumina was obtained at 50°C, whereas minimum μ of 0.77 and 0.52 against AISI 52100 and Alumina was obtained at RT. Optical microscopy, SEM, EDXA and 3D profilometery have been used to understand the friction and wear mechanism of tribopair. From these observations it is concluded that wear of D2 steel is minimum for particular range of load and temperature. The results obtained are useful for designers and engineers working in the field of cold forming.N allotropes of carbon, including carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs), show a great deal of promise as functional fillers in nanocomposite materials. The extreme linear aspect ratios, strong sp2 carbon bonds, and high chemical stability all contribute to making CNTs ideal reinforcement fillers for mechanical applications. Conversely, the high aspect ratio planar nature of graphene and GNPs, along with their high impermeabilities, suggests applications as barrier materials. In this talk, we discuss our work on CNT – aluminum oxide (AO) composites for mechanical applications, including as ballistic armour, and GNP – polymer composites for high barrier applications, including oxygen barriers for food packaging and anti-corrosion coatings. CNT – AO hybrid structures are produced by depositing CNTs as conformal coatings on various AO materials, including powders and fabrics. The deposition is carried out in a large-volume chemical vapor deposition reactor, following a conformal catalyst deposition from solution or via an atomic layer deposition process. The CNT – AO hybrids are sintered into composite materials under high pressure and characterized for mechanical enhancements. Increase in fracture toughness of as high as 71% have been found from these CNT – AO composites. GNP materials are melt-processed with polyethylene (PE) and extruded into packaging films, which are characterized for their oxygen transmission rates. It is found that the GNP – PE films show comparable oxygen transmission rates to the neat PE films, indicating that further processing will be necessary to realize the desired enhancements. The GNP materials are also solution processed with epoxy (EP), cast onto steel substrates, and cured to form coatings. The efficacy of these coatings as anti-corrosion barriers is established by electrochemical and salt-fog corrosion tests. Early results suggest that the GNPs are enhancing the anti-corrosion performance of the EP films.Statement of the Problem: Antimicrobial materials based on various nanoparticles has attracted huge attention in last few decades because of the cheapness, easiness to use, and effectiveness in preventing annexation and proliferation of microbes on material surfaces. Paper has been used in many applications as a matrix to carry the nanoparticles due to its high porosity, considerable mechanical strength, and high availability. Silver nanoparticles (AgNPs) have widely been used as antibacterial/ antifungal agents in a varied range of consumer products because of their large active surface area. However, effective methods for immobilizing AgNPs on cellulose paper or similar surfaces for various applications are inadequately advanced.C features of certain materials are self-similar. This phenomenon is recognizable by scaling of measurement data corresponding to the considered self-similar feature. To perform scaling, we apply notion of homogenous function in general sense. For two independent variables such a function reads P(f,B)=Bβ F(f/Bα), where P is a considered magnitude, α and β are scaling exponents, F(∙) is an arbitrary continuous function, where α, β and F(∙) have to be determined by the measurement data. Definition of P(f,B) enables us to transform all characteristics P(f,B) to the one universal function of the one variable: P(f,B)/ Bβ =F(f/Bα). This effect is so called the data collapse and can be applied for comparison of measurement, data measured in different laboratories, which enable us to estimate quality of each laboratory series. Another application of the data collapse is compression of large experimental data. If the considered data are produced by a self-similar system then one can store them in a form of continuous curve. The data collapse enables us to introduce an absolute dimensionless characteristic: P = f• (f+1), where P and f are dimensionless P and f, respectively. This characteristic divide {P, f } space into the two independent subspaces of material’s characteristics. Finally, the scaling supplemented by pseudo-equation of states plays basic role in creation of algorithms for designing of modern materials. The presented results are based on experimental data of soft magnetic materials and soft magnetic composites. Where, P (f,B) is density of power loss, f is frequency of the field’s modulation and B is maximum of magnetic induction. One can apply this simple mathematics to any self-similar object. However, ultimately one must say that the degree of success achieved when applying the scaling depends on the property of the data. The data must obey the scaling.A homeostasis and pH regulation inside the body is precisely controlled by kidney, lungs and buffer systems, because even a minor change from the normal value could severely affect many organs. Blood and urine pH tests are common in day-to-day clinical trials without much effort. Still, there is great demand for in-vivo pH testing to understand more about body metabolism and to provide effective treatments during diagnosis. The detection of pH at the single-cell level is hoping for the great level of clinical importance for the early detection of many diseases like cancer, diabetes, etc. In this research work, we have fabricated a micro region pH sensor by series of processes like electrolytic polishing to create needle structure, deposition of electrode materials using RF magnetron sputtering for pH measurements and finally testing in various biological mediums. Working and reference electrodes were Ag/AgIO3 and Sb/Sb2O3 deposited on microneedles under optimized deposition parameters. The structural, elemental and morphological properties were analyzed using XRD, XPS, EDS and FE-SEM. The fabricated tip of the microneedle probe is around 5 μM analyzed by FE-SEM which size is comparable with the biological cells. pH testing initially began with using fish egg and various biological cells. The obtained pH sensing results were adequate with theoretical values. Since the sensor works at micro region, the potential difference is easily disturbed by atmospheric anomalies. Hence, many steps have been taken to improve the stability of the sensor. Besides that, fabricated microneedle sensor ability is proved through in-vivo testing in mice cerebrospinal fluid (CSF) and bladder. The pH sensor reported here is totally reversible and results were reproducible after several routine tests.I closed cycle gas turbine, turbine blades are subjected to severe wear because of high contact temperature and pressure. Inconel 718 is used as a blade material for closed cycle gas turbine applications; however, its friction and wear properties have been studied fully under high stress and high temperature conditions. Friction and wear behavior of Inconel 718 against silicon nitride and alumina have been studied under dry sliding conditions in temperature range of 40-500°C using ball-ondisc universal tribometer. For sliding distance test the wear rate of Inconel 718 with alumina is less than silicon nitride for the entire range at 500°C. The wear volume of Inconel 718 increases with the increase in sliding distance increases from 200 m to 1000 m against alumina and silicon nitride. For Inconel 718 highest coefficient of friction (μ) of 0.88 and 0.52 against alumina and silicon nitride was obtained at 10 N, whereas minimum μ of 0.45 and 0.40 against alumina and silicon nitride was obtained at 20 N, these tests carried out at 500°C. For temperature test highest coefficient of friction (μ) 0.75 at 400°C and lowest μ 0.46 at 200°C against silicon nitride whereas highest coefficient of friction (μ) 0.88 at 200°C and lowest μ 0.54 at 500°C against alumina. Optical microscopy, SEM, EDXA, and 3-D profilometery have been used to understand the friction and wear mechanism of tribopair. From these observations it is concluded that wear of Inconel 718 is minimumW a growing number of high precision tools for studying biological systems, it is important to develop traceable quantitative methods that result in accurate measurements. Because biological systems are both complex and fluxional, context is vitally important for such measurements in order for them to be accurate. Correlation of measurements through space and time can provide such quantitative assessments. Metallic nanoparticles pose many challenges for measurement in cellular systems. The metal can interfere with the detection method and the particles can change in size and shape over time and in association with different biological molecules. At the National Research Council, we seek to correlate detailed physical characterization of silver nanoparticles with biological measurements to generate methods for measuring the impact of nanosilver on different cell types and quantifying the specific interactions of nanosilver with biological molecules. Correlating changes in nanoparticles over time in biological fluids helps to provide an understanding of nanoparticle behaviour and results in higher reproducibility of observed biological endpoints. Surface coatings play a pivotal role in recognition of the particles by cellular receptors suggesting active transport plays a critical role in the nanosilver life cycle. Physical and chemical differences between silver nanoparticles and changes that occur in biological test media can be correlated to toxicity, and different mechanisms for toxicity are apparent. Uptake rates and localization is also different between different cell lines. Uptake and localization of particles provides evidence that nanosilver should not be treated as a single material but should be studied as an array of materials with different properties in different biological systems.

Fuel cells as an energy source for desalination applications.

Nowadays, there is a renewed interest in fuel cell technology from industry and academia, electrochemistry and catalysis scientists. This interest is due to environmental legislations for CO2 and other greenhouse gases emissions (United Nations Environment Programme and the World Trade Organization, 2009) that demand the use of high efficiency energy production systems. Such systems have great potential in the area of desalination technology (Kenet, 2003, Al-Hallaj et al., 2004, Singh, 2008, Wang et al. 2011, Jones, 2013). Fuel cells are characterised by high operation efficiency, which results in decreased fuel consumption, and low environmental impact. A fuel cell is a device that converts the chemical energy of a fuel directly into electricity through electrochemical reactions, with low waste heat (e.g. SOFC in Fig. 1). The first fuel cell was fabricated back in 1830s, and slow but steady progress has been made toward their commercialization since then.

Nanoindentation evaluation of suspension thermal sprayed nanocomposite WC-Co coatings

The aim of this paper is to evaluate the microstructural and nanohardness characteristics of tungsten carbide-cobalt (WC-Co) cermet coatings deposited by liquid suspension spraying. Commercially available WC-Co coating powder was milled and water based suspension was produced as feedstock for the thermal spray coating process. Microstructural evaluations of WC-Co cermet coatings included XRD (X-Ray Diffraction) and SEM (Scanning Electron Microscopy). Post spraying nanomechanical evaluations were conducted using a Berkovich nanoindenter. Results indicated relatively higher modulus but lower hardness of suspension coatings. The load displacement curves during nanoindentation were characteristic of the complex coating microstructure showing signs of microcracking and pile-up.

Microstructural Evaluation of Suspension Thermally Sprayed WC-Co Nanocomposite Coatings

Microstructural and sliding wear evaluations of nanostructured coatings deposited by Suspension High Velocity Oxy-Fuel (S-HVOF) spraying were conducted in as-sprayed and HIPed (Hot Isostatically Pressed) conditions. S-HVOF coatings were nanostructured via ball milling of the WC-12Co start powder, and deposited via an aqueous based suspension using modified HVOF (TopGun) spraying. Microstructural evaluations of these hardmetal coatings included TEM (Transmission Electron Microscopy), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Sliding wear tests were conducted using a ball-on-flat test rig. Results indicated that nanostructured features inherited from the start powder in S-HVOF spraying were retained in the resulting coatings. The decarburisation of WC due to a higher surface area to volume ratio was also observed in the S-HVOF coatings. Nanostructured and amorphous phases caused by the high cooling rates during thermal spraying crystallized into complex eta-phases after the HIPing treatment. Sliding wear performance indicated that the coating wear was lower for the HIPed coatings.

Single Asperity Scratch Behaviour of Cast Stellite 6 Alloy

The aim of this paper is to investigate the nano-scale sliding wear behaviour of cast Stellite 6 (Co-28Cr-4.5W-1C) with a view to comprehend single asperity deformation. A nanoindentation system (NanoTest\(^{\mathrm{TM}}\)—Micro Materials Limited, UK) equipped with wear testing module was used to simulate single asperity deformation behaviour using a sphero-conical indenter of 10 \(\upmu \)m tip radius, 60\(^{\circ }\) included angle for a sliding distance of 60 \(\upmu \)m under 50 and 100 mN load, with sliding velocity of 2 \(\upmu \)m/s. The test load was increased linearly over the sliding distance. Post-test evaluations included X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements to determine the failure mode and wear volume. An elastic-plastic finite element model (FEM) was used to compare the displaced volume of alloy with the experimental data. There is limited work available to understand the nanotribological properties of Stellite alloys in published literature. In the current investigation results are discussed in terms of microstructural and tribo-mechanical evaluations to provide an understanding of the structure-property relationships. Results indicate that the wear behaviour at the nano-scale was dominated by the interaction of interdentritic carbides and metal matrix. It can be concluded that nano-scale sliding wear behaviour of cast Stellite 6 alloy is controlled by single asperity deformation. The predictions of nano-scale elastic-plastic FEM to calculate the volume displaced by the scratch are also discussed.