In this article, the tribological behavior and energy efficiency of surfaces coated with WC-CoCr/HVOF were evaluated after a laser remelting process, using low and high laser energy densities, ...respectively, 33.3 and 150 J/mm2. The purpose of laser remelting was to adequately modify the microstructure of the coatings and promote better performance during surface sliding. Therefore, the microstructure, phase composition and microhardness of the coatings were investigated, and heat effect on the substrate. During dry and lubricated tribological tests, friction coefficient (COF), wear, and surface roughness also were evaluated. In the dry tests, friction, wear and heat dissipation energies were obtained, which were then correlated with the energy consumed by the tribometer. A HEPR-type biodegradable oil was used in the lubricated tests. The proper formation of W2C and Co3W3C, obtained for the lower energy density, increased the hardness, without weakening the material, while the CrC phase acted as an anti-wear barrier. Whereas for the high energy density, thermal decomposition produced fragile phases, which were easily removed from the matrix during the wear test. The sample tested in as-sprayed condition had a high adhesion and friction compared to the remelted samples. On the remelted surfaces, greater friction stability was obtained. The lower dry friction was not linked to the lower power consumption, a result which was then attributed to the higher heat dissipation from the surface during the tests. Finally, this study proposes a methodology for quantifying the efficiency of sliding surfaces and points to a sustainable solution for tribology.
•An energy-based mathematical model was developed to estimate the sliding efficiency.•A non-linear behavior between laser energy and coating microhardness was obtained.•Laser remelting in the coating lowers COF but not necessarily energy consumption.•The adequate distribution of W2C, Co3W3C and CrC increases the resistance to wear.•The sustainable combination of laser remelting with HEPR oil reduced COF and wear.
A thermal analysis in laser welding using inverse problems Magalhães, Elisan dos Santos; Paes, Luiz Eduardo dos Santos; Pereira, Milton ...
International communications in heat and mass transfer,
March 2018, 2018-03-00, Letnik:
92
Journal Article
Recenzirano
Odprti dostop
The heat flux inverse analysis is significantly affected by the heat flux distribution in laser welding simulation. This work proposed a different approach for the heat distribution which predicts ...the temperature and the weld bead in laser welding. The influence of the heat flux distribution in an inverse heat conduction problem applied on laser welding simulation is studied by comparing different heat distribution models. An inverse heat conduction algorithm based on the three-dimensional (3D) heat diffusion equation and the enthalpy function to model the phase change problem are used to estimate the heat flux under different heat distributions. The Time Traveling Regularization is applied with the Golden Section method to estimate the heat flux in the studied cases. The proposed cubic root and square root of the volumetric heat distribution presented a good agreement between the weld profile and the experimental temperatures. The heat rate estimation proves to be dependent on the heat distribution. The proposed methodology is an alternative to predict the weld bead profile and the thermal efficiency in low penetration laser welding.
Ni-superalloys coatings deposited via laser metal deposition (LMD) have been known to perform well in increasing components lifespan and consequently reducing production and repair costs. Although ...most of these coatings already present good results in its hardness, and tribological behavior, some can be improved by post-deposition treatments, such as laser remelting. In this ambit, the present paper aims to evaluate the laser remelting posttreatment effects on the Ni-Cr-B-Si coating sliding tribological behavior. For this, two conditions were compared: Ni-Cr-B-Si coating as-deposited and Ni-Cr-B-Si coating as-deposited and remelted. The coating’s occurrence of superficial macro defects, their microhardness, and tribological performance in the pin-on-disk (ASTM G99) test were compared. Friction coefficient (load cell), volumetric loss (optical interferometry), Archard's wear coefficient and worn surfaces (SEM and EDS), were evaluated. Results show that the laser remelting posttreatment was effective in reducing cooling cracks, increasing hardness and reducing friction coefficient oscillation and volumetric loss average.
A coleta e a destinacao dos residuos solidos preocupam de forma cada vez mais intensa, a opiniao publica e as administracoes municipais. Algumas medidas tem sido realizadas, e preliminarmente ...apresentam bons resultados, um deste empreendimento e a USINA VERDE, que recebe diariamente 30 toneladas de residuos solidos. Estes sao separados em funcao da possibilidade de reutilizacao ou de reciclagem e o restante e incinerado, gerando energia e subprodutos. Contudo, mesmo apresentando um conjunto de beneficios ambientais, este empreendimento precisa ser alvo de avaliacoes de impactos ambientais de forma constante. O objetivo deste artigo e avaliar os principais impactos esperados nas diversas fases do empreendimento, nomeadamente as de implantacao e operacao da USINA VERDE, atraves da matriciacao e modelagem matematica dos mesmos. A metodologia proposta se prestou ao seu objetivo, demostrando de forma clara que o empreendimento estudo e viavel do ponto de vista ambiental, desde que sejam implementados programas de mitigacao dos seus impactos. Palavras-chave: Impacto ambiental, Residuos solidos, Avaliacao d e impactos ambientais. The collection and disposal of solid waste is increasingly worrying public opinion and municipal administrations. Some measures have been carried out and shows good preliminary results. One such example is USINA VERDE, which receives 30 tons of solid waste daily. The waste is segregated according to the possibility of reuse or recycling and the rest is incinerated, generating energy and by-products. However, even presenting a set of environmental benefits, the facility needs to be the target of environmental impact assessments on a constant basis. The objective of this article is to evaluate the main expected impacts in the various phases of the project namely those of implementation and operation of USINA VERDE, through matrix support and mathematical modeling of them. The proposed methodology shows that the facility is environmentally viable, provided that programs to mitigate its impacts are implemented. Keywords: Environmental impact, Solid waste, Environmental impact assessment. La recoleccion y disposicion de residuos solidos es una preocupacion creciente para la opinion publica y las administraciones municipales. Algunas medidas se han llevado a cabo y preliminarmente muestran buenos resultados, uno de estos emprendimientos es la USINA VERDE, que recibe diariamente 30 toneladas de residuos solidos. Estos se separan en funcion de la posibilidad de reutilizacion o reciclaje y el resto se incinera generando energia y subproductos. Sin embargo, aun presentando un conjunto de beneficios ambientales, este proyecto necesita ser objeto de constantes evaluaciones de impacto ambiental. El objetivo de este articulo es evaluar los principales impactos esperados en las diferentes etapas del emprendimiento, a saber, la implantacion y operacion de la USINA VERDE, a traves de su matrizacion y modelacion matematica. La metodologia propuesta cumplio su proposito, demostrando claramente que el proyecto en estudio es viable desde el punto de vista ambiental, siempre y cuando se implementen programas para mitigar sus impactos. Palabras clave: Impacto ambiental, Residuos solidos, Evaluacion de impactos ambientales.
Improving the performance of mechanical components and reducing machine energy consumption involves the correct selection of lubricants and their contact surfaces. The use of biodegradable hydraulic ...fluids along with less environmental impact surfaces is one example. In this sense, the following paper aims to analyze the behavior of mineral oil (HLP) and biodegradable oils (HEPR and HETG) submitted to a sliding with pins manufactured in PTFE and Al2O3 against a flat substrate coated with FeCrNiMo by the Laser Directed Energy Deposition (L-DED) process. Coatings by this replacement deposition process are proving to be a promising alternative in the replacement of hard chromium, a harmful material to human health. The slip tests were performed in a pin-on-disk tribometer using different loads in order to assess lubrication and wear regimes. In the tests, the average of the friction coefficients (μ) obtained was μHETG = 0.072, μHLP = 0.026 and μHEPR = 0.011, besides well-defined lubrication regimes. In the wear analysis, it was observed that the highest concentrations of Zn and P additives, found in HEPR, reduced surface damage. The main wear mechanisms identified were scratching, microcracking, microploughing and detachment. Consistent with the results mentioned, the largest volume removed from the coating was with the use of HETG vegetable oil, about 41% more than HEPR.
This study investigated the effects of a maternal dyslipidaemic (DLP) diet on lipid metabolism, microbial counts in faeces and hepatic and intestinal morphology in rat offspring with respect to sex ...during different phases of life. Wistar rats (dams) were fed a control (CTL) or DLP during gestation and lactation. After weaning, CTL and DLP offspring were fed a standard diet. The effects of a maternal DLP on body composition, biochemical parameters, faecal microbiota and intestinal and hepatic histomorphometric characteristics in rat offspring were evaluated at 30 and 90 d of age. The DLP diet during gestation and lactation caused lower birth weight and a greater weight gain percentage at the end of the 90-d period in both male and female offspring. Female pups from DLP dams had higher liver fat levels compared with CTL (P≤0·001) at 90 d of age. Males from DLP dams had greater visceral fat weight and lower Lactobacillus spp. faecal counts at 90 d of age (P≤0·001) as well as lower faecal fat excretion (P≤0·05) and Bacteroides spp. faecal counts (P≤0·001) at 30 d of age when compared with pups from CTL dams. However, both dams and DLP pups showed damage to intestinal villi. A maternal DLP alters intestinal function and lipid metabolism in a sex-specific manner and is a potential predisposing factor for health complications in offspring from the juvenile period to the adult period.
Efflux pumps are proteins present in the plasma membrane of bacteria, which transport antibiotics and other compounds into the extracellular medium, conferring resistance. The discovery of natural ...efflux pump inhibitors is a promising alternative. α-Bisabolol is a sesquiterpene isolated from several plants such as
L. and has important properties such as antibacterial and anti-inflammatory activity. Currently, the formation of inclusion complexes with β-Cyclodextrin has been used for improving the physicochemical characteristics of the host molecule. This study evaluated the effect of α-Bisabolol, in isolation and in complexation with β-Cyclodextrin, as TetK and NorA efflux pump inhibitors in
strains. The minimum inhibitory concentration (MIC) was determined. Subsequently, inhibitory activity over the pumps was observed by an MIC reduction for the antibiotics, by using subinhibitory concentrations (MIC/8) in combination with tetracycline and norfloxacin. The MIC of the compounds was ≥1024 μg/mL. α-Bisabolol potentiated the action of tetracycline and reduced the MIC of norfloxacin to a clinically relevant concentration. The complexed substance showed synergism however, the effect of the isolated α-Bisabolol was superior to the complex. These results indicate α-Bisabolol is a potential substance to be used as an efflux pump inhibitor.
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