2,877 research outputs found
Investigation into laser re-melting of inconel 625 HVOF coating blended with WC
No full textHigh velocity oxy-fuel (HVOF) spraying of Diamalloy 1005 powders mixed with WC particles onto steel (304) is considered and laser re-melting of the resulting coatings is examined. Laser re-melting process is modeled to determine the melt layer thickness while temperature increase is formulated using the Fourier heating law. The morphological and metallurgical analyses prior and post laser re-melting process are carried out using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). X-ray diffraction (XRD) technique is used to determine the residual stress developed in the coating while the analytical formulation is adopted to predict the residual stress levels at the coating base material interface. The indentation tests are carried out to determine the Young’s modulus and fracture toughness of the coating prior to laser re-melting. Corrosion resistance of coating is measured using potentiodynamic polarization technique prior and post laser treatment process. The predictions of the melt layer thickness are in good agreement with experimental results. The presence of WC particles modifies temperature rise and its gradient in the coating while affecting the Young’s modulus, residual stress levels, and fracture toughness of the coating. The differences in the thermal properties of Inconel 625 powders and WC particles result in formation of small size cellular structure through polyphase solidification. WC dissolution in the central region of the large polycrystalline cells is observed due to the loss of carbon through carbonic gas formation. The results of corrosion tests prevail that significant improvement of corrosion resistance can be achieved after laser treatment process
Clinical Utility of a Commercial LAM-ELISA Assay for TB Diagnosis in HIV-Infected Patients Using Urine and Sputum Samples
No full textBackground: The accurate diagnosis of TB in HIV-infected patients, particularly with advanced immunosuppression, is difficult. Recent studies indicate that a lipoarabinomannan (LAM) assay (Clearview-TB (R)-ELISA) may have some utility for the diagnosis of TB in HIV-infected patients; however, the precise subgroup that may benefit from this technology requires clarification. The utility of LAM in sputum samples has, hitherto, not been evaluated.Methods: LAM was measured in sputum and urine samples obtained from 500 consecutively recruited ambulant patients, with suspected TB, from 2 primary care clinics in South Africa. Culture positivity for M. tuberculosis was used as the reference standard for TB diagnosis.Results: Of 440 evaluable patients 120/387 (31%) were HIV-infected. Urine-LAM positivity was associated with HIV positivity (p = 0.007) and test sensitivity, although low, was significantly higher in HIV-infected compared to uninfected patients (21% versus 6%; p<0.001), and also in HIV-infected participants with a CD4 <200 versus <200 cells/mm(3) (37% versus 0%; p = 0.003). Urine-LAM remained highly specific in all 3 subgroups (95%-100%). 25% of smear-negative but culture-positive HIV-infected patients with a CD4 <200 cells/mm(3) were positive for urine-LAM. Sputum-LAM had good sensitivity (86%) but poor specificity (15%) likely due to test cross-reactivity with several mouth-residing organisms including actinomycetes and nocardia species.Conclusions: These preliminary data indicate that in a high burden primary care setting the diagnostic usefulness of urine-LAM is limited, as a rule-in test, to a specific patient subgroup i.e. smear-negative HIV-infected TB patients with a CD4 count <200 cells/mm(3), who would otherwise have required further investigation. However, even in this group sensitivity was modest. Future and adequately powered studies in a primary care setting should now specifically target patients with suspected TB who have advanced HIV infection
Obtaining Crack-free WC-Co Alloys by Selective Laser Melting
No full textAbstractStandard hardmetals of WC-Co system are brittle and often crack at selective laser melting (SLM). The objective of this study is to estimate the range of WC/Co ratio where cracking can be avoided. Micron-sized Co powder was mixed with WC nanopowder in a ball mill to obtain uniform distribution of WC over the surface of Co particles. Continuous layers of remelted material on the surface of a hardmetal plate were obtained from this composite powder by SLM at 1.07μm wavelength. The layers have satisfactory porosity and are well bound to the substrate. The chemical composition of the layers matches the composition of the initial powder mixtures. The powder mixture with 25wt.%WC can be used for SLM to obtain materials without cracks. The powder mixture with 50wt.%WC cracks because of formation of brittle W3Co3C phase. Cracking can considerably reduce the mechanical strength, so that the use of this composition is not advised
Abrasive wear behaviour of detonation sprayed WC-Co coatings on mild steel
No full textThe main objective of the present investigation is to evaluate the abrasive wear behaviour of detonation sprayed WC-Co coatings and to compare them with plasma sprayed WC-Co coatings and carburised and nitrided surfaces. Mild steel was coated with WC-12Co and WC-17Co using detonation and plasma guns. The abrasive wear rates of these coatings were determined at three different loads and compared with wear rates of as received, carburised, and nitrided mild steel. The abraded surfaces and the surfaces beneath the abraded surfaces were characterised by SEM. The results indicate that the detonation sprayed WC-12Co coating has the best abrasive wear resistance at all loads. Maximum improvement in wear resistance is obtained at an intermediate load (i.e. at 5 kg). The wear of detonation sprayed coatings is by abrasion of the soft Co matrix followed by the pullout of hard WC particles
Porosity control of in situ forming tungsten carbide in laser additive manufacturing (LAM)
No full textThe effect of powder compression on the formation of porosity when heating with a laser beam has been investigated. The starting materials were elemental powders of Fe, W and C which were locally melted to form WC in Fe matrix by an in situ laser additive manufacturing (LAM) process. The resulting microstructures have been studied and chemical analysis has been performed. The main application for the process is for the production of WC based or carbide cutting tooling by very accurate deposition of hard-facing materials onto a steel substrate. Fe is used as the matrix material since ferrous alloys are employed as the substrate for these applications
A Quick Guide to Pediatric Retina
No full textThis book is intended to provide a quick guide to the field of pediatric retina. It has been long accepted that retinal disorders in children differ from those in adults. Although there are plenty of published books on retinal diseases, most of them only cover adult retinal disorders. Therefore, information on pediatric retinal diseases is urgently needed. The book combines comprehensive information with rich illustrations to offer readers an in-depth understanding of the two main themes: retinopathy of prematurity (ROP) and other pediatric vitreoretinal disorders. World-renowned pediatric retina experts share their insights and research findings in areas such as ROP, familiar exudative vitreoretinopathy, Coats disease, retinoblastoma, congenital x-linked retinoschisis and hereditary retinal diseases. Topics concerning modern and future medicine such as tele-screening for ROP, E-learning for ROP, and deep learning for ROP are also included. Designed to help readers understand the contents as quickly as possible, the book includes many useful tips and pearls, as well as easy-to-follow figures. It covers the majority of pediatric retinal diseases and offers essential information on their diagnosis and management. In addition, relevant and up-to-date references are provided for those who want to explore the topics in more depth. As such, the book offers an excellent reference guide to caring for these young patients
Electricity consumption in Hong Kong: trend analysis and greenhouse gases emission
No full textThe consumption of electricity has increased continuously in the past four decades. Inevitably, the emission of greenhouse gases has increased in the same period even though Hong Kong’s power companies have produced a certain percentage of electricity using “cleaner” fuels such as natural gas and nuclear power in recent years. This paper presents a four-parameter logistic model (To WM, Lai TM, Lo WC, Lam KH, Chung WL. The growth pattern and fuel life cycle analysis of the electricity consumption of Hong Kong. Environ Pollut. 2012;165:1–10) that describes the growth pattern of Hong Kong’s overall electricity consumption. The same approach was used to model the sectoral electricity consumption in Hong Kong. In addition, a fuel life cycle analysis was used to determine greenhouse gases emission due to electricity consumption. It was found that the emission factor due to the electricity generated in Hong Kong was 0.824 kg CO2-equivalent per kWh while the emission factor due to the electricity consumed in Hong Kong was 0.751 kg CO2-equivalent per kWh, as 23% of the electricity consumed was imported (net import) from the Daya Bay Nuclear Power Plant located in Shenzhen in 2012. Future electricity demand is presented
A Quick Guide to Pediatric Retina
No full textThis book is intended to provide a quick guide to the field of pediatric retina. It has been long accepted that retinal disorders in children differ from those in adults. Although there are plenty of published books on retinal diseases, most of them only cover adult retinal disorders. Therefore, information on pediatric retinal diseases is urgently needed.
The book combines comprehensive information with rich illustrations to offer readers an in-depth understanding of the two main themes: retinopathy of prematurity (ROP) and other pediatric vitreoretinal disorders. World-renowned pediatric retina experts share their insights and research findings in areas such as ROP, familiar exudative vitreoretinopathy, Coats disease, retinoblastoma, congenital x-linked retinoschisis and hereditary retinal diseases. Topics concerning modern and future medicine such as tele-screening for ROP, E-learning for ROP, and deep learning for ROP are also included.
Designed to help readers understand the contents as quickly as possible, the book includes many useful tips and pearls, as well as easy-to-follow figures. It covers the majority of pediatric retinal diseases and offers essential information on their diagnosis and management. In addition, relevant and up-to-date references are provided for those who want to explore the topics in more depth. As such, the book offers an excellent reference guide to caring for these young patients
Abrasion resistant glass-ceramic coatings reinforced with WC-nanoparticles
No full text© 2021 The Author(s)The glass ceramic coatings reinforced with nano-WC hard ceramic particles used in the study were designed to remove stress points in the vitreous matrix. Coatings were applied to cast iron surfaces by the wet spraying method and fired at 770 °C for 12 min. The abrasion resistance of the samples was evaluated with a Taber abrasion device with H18 wheels and the changes in SEM, color, gloss, mass loss, and surface roughness values were analyzed before and after the abrasion test of the samples. The results showed that, the addition of 2.5 wt% nano-WC (W25) created the lowest mass loss and the lowest change in the surface properties. The lowest amount and the size in the pores were also observed in the W25 sample. It was observed that agglomeration occurred with the increase of nano-WC ratio in the samples and the abrasion resistance decreased
Composition regulation of composite materials in laser powder bed fusion additive manufacturing
No full textUnderstanding and controlling the composition segregation during powder spreading is of key importance in the additive manufacturing (AM) of composite materials. Under this circumstance, the segregation behavior of WC/316 L composite powders during spreading in laser powder bed fusion (LPBF) AM was numerically investigated by the discrete element method. The effects of process conditions (i.e., spreader velocity and geometry) and powder properties (i.e., size and shape of the WC powder) on the powder bed composition segregation and related characteristics were systematically analyzed. Corresponding mechanisms were identified from microscopic scale in terms of particle velocity, motion trajectory, mechanical behavior, and energy information. Finally, proper solutions in designing and constructing WC/316 L composite materials with desired gradient structures were proposed. The results show that the small blade velocity (V) will enhance the negative segregation, increase the average packing density ρ¯, and decrease uniformity ρvc in the WC/316 L composite powder bed. Compared with the blade, the roller can increase the negative segregation (Seroller = −0.027 < Seblade = −0.019) and the average packing density (ρ¯roller = 0.31>ρ¯blade = 0.20). When the WC/316 L size ratio increases from 25 μm/45 μm to 45 μm/45 μm, the negative segregation becomes weaker, and its value increases from −0.084 to −0.007. When the size ratio increases to 65 μm/45 μm, the powder behaves positive segregation with Semax = 0.017; in this case, the packing density is the lowest (0.14), and the uniformity is the worst (0.17). In comparison with spherical shape, polyhedral WC powder can reduce the negative segregation of the powder bed (Sesphere = −0.019 < Sepolyhedron = −0.008), while the WC shape has less effect on the packing density and uniformity. The density difference of the WC and 316 L powders leads to the difference in energy and force, resulting in different motion and segregation behaviors in the composite powder bed. For WC/316 L composite powder with a fixed composition, the condition of V = 0.025 m/s, WC/316 L size ratio = 25 μm/45 μm, roller spreader, and spherical WC can realize the proper composition gradient along the spreading direction in the composite powder bed.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Resources & Recyclin
- …
