TRIBO-MECHANICAL CHARACTERIZATION OF ENB ALLOY COATINGS: EFFECT OF HEAT-TREATMENT TEMPERATURE AND SODIUM BOROHYDRIDE CONCENTRATION

Previously electroless Ni-B (ENB) coatings were analyzed and optimized based on various coating parameters. However, variation of nano-indentation behaviour like nano-hardness, elastic modulus and scratch hardness variation with bath composition and heat treatment temperature has not been reported earlier. An attempt has been made to explore the same in the present study. ENB coating layers are deposited on AISI 1040 steel specimen with varying concentration of  sodium borohydride (NaBH4) and heat-treated at 350°C, 450°C and 550°C to investigate the related effects. Nano-hardness and elastic modulus of as-coated specimens are found to improve with NaBH4 concentration due to increased boron content and nodule size. Both nano-hardness and elastic modulus are observed to improve further upon heat treatment because of incorporation of various boride phases leading to compact morphology and increased size of the nodules. Scratch hardness value also increases with NaBH4 concentration and it improves further upon heat treatment and reaches to its maximum at 450°C due to presence of compact and hard Ni2B phase. Compact homogeneous surface morphology enhances the friction and wear behaviour of the heat-treated coatings even though surface roughness deteriorates after heat treatment.

Paraparesis Following Spinal Anesthesia in a Patient After Cesarean Section: A Rare Entity

Paraparesis, as a complication after spinal anesthesia, is very rare. It may occur due to presence of undiagnosed spinal tumor or spinal shock after lumbar puncture. We describe a 22-year-old mother who had cesarean section under spinal anesthesia and developed paraparesis in postoperative period. She had history of facial palsy and hearing impairment for last 9 years. Magnetic resonance imaging (MRI) revealed spinal space-occupying lesion (extramedullary meningioma) at D-5/D-6 level. Careful observation and examination in postoperative period after regional anesthesia is necessary for early diagnosis and management

Optimization of wear behavior of electroless Ni-P-W coating under dry and lubricated conditions using genetic algorithm (GA)

The present study aims to investigate the tribological behavior of Ni-P-W coating under dry and lubricated condition. The coating is deposited onto mild steel (AISI 1040) specimens by the electroless method using a sodium hypophosphite based alkaline bath. Coating characterization is done to investigate the effect of microstructure on its performance. The change in microhardness is observed to be quite significant after annealing the deposits at 400°C for 1h. A pin–on–disc type tribo-tester is used to investigate the tribological behavior of the coating under dry and lubricated conditions. The experimental design formulation is based on Taguchi’s orthogonal array. The design parameters considered are the applied normal load, sliding speed and sliding duration while the response parameter is wear depth. Multiple regression analysis is employed to obtain a quadratic model of the response variables with the main design parameters under considerations. A high value of coefficient of determination of 95.3% and 87.5% of wear depth is obtained under dry and lubricated conditions, respectively which indicate good correlation between experimental results and the multiple regression models. Analysis of variance at a confidence level of 95% shows that the models are statistically significant. Finally, the quadratic equations are used as objective functions to obtain the optimal combination of tribo testing parameters for minimum wear depth using genetic algorithm (GA)

Modeling and Optimization of Fractal Dimension in Wire Electrical Discharge Machining of EN 31 Steel Using the ANN-GA Approach

To achieve enhanced surface characteristics in wire electrical discharge machining (WEDM), the present work reports the use of an artificial neural network (ANN) combined with a genetic algorithm (GA) for the correlation and optimization of WEDM process parameters. The parameters considered are the discharge current, voltage, pulse-on time, and pulse-off time, while the response is fractal dimension. The usefulness of fractal dimension to characterize a machined surface lies in the fact that it is independent of the resolution of the instrument or length scales. Experiments were carried out based on a rotatable central composite design. A feed-forward ANN architecture trained using the Levenberg-Marquardt (L-M) back-propagation algorithm has been used to model the complex relationship between WEDM process parameters and fractal dimension. After several trials, 4-3-3-1 neural network architecture has been found to predict the fractal dimension with reasonable accuracy, having an overall R-value of 0.97. Furthermore, the genetic algorithm (GA) has been used to predict the optimal combination of machining parameters to achieve a higher fractal dimension. The predicted optimal condition is seen to be in close agreement with experimental results. Scanning electron micrography of the machined surface reveals that the combined ANN-GA method can significantly improve the surface texture produced from WEDM by reducing the formation of re-solidified globules

Comparative Study of Tribological Behavior of Electroless Ni–B, Ni–B–Mo, and Ni–B–W Coatings at Room and High Temperatures

Ni–B alloys deposited by the electroless method are considered to be hard variants of the electroless nickel family. Inclusion of Mo or W to form ternary alloys improves the thermal stability of electroless nickel coatings. Therefore, in the present work, Ni–B, Ni–B–Mo, and Ni–B–W coatings are deposited; and their tribological behavior at room and high temperatures are investigated. Electroless Ni–B, Ni–B–Mo, and Ni–B–W coatings are deposited on AISI 1040 steel substrates. The coatings are heat treated to improve their mechanical properties and crystallinity. Tribological behavior of the coatings is determined on a pin-on-disc type tribological test setup using various applied normal loads (10–50 N) and sliding speeds (0.25–0.42 m/s) to measure wear and coefficient of friction at different operating temperatures (25 °C–500 °C). Ni–B–W coatings are observed to have higher wear resistance than Ni–B or Ni–B–Mo coatings throughout the temperature range considered. Although for coefficient of friction, no such trend is observed. The worn surface of the coatings at 500 °C is characterized by lubricious oxide glazes, which lead to enhanced tribological behavior compared with that at 100 °C. A study of the coating characteristics such as composition, phase transformations, surface morphology, and microhardness is also carried out prior to tribological tests

Fe-exchanged nano-bentonite outperforms Fe3O4 nanoparticles in removing nitrate and bicarbonate from wastewater

Nitrate (NO3−) and bicarbonate (HCO3−) are harmful for the water quality and can potentially create negative impacts to aquatic organisms, crops and humans. This study deals with the removal of NO3− and HCO3− from contaminated wastewater using Fe-exchanged nano-bentonite and Fe3O4 nanoparticles. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, surface area measurement and particle size analysis revealed that the adsorbents fall under the nano-scale size range with high specific surface area, and Fe was successfully exchanged in the nano-bentonite clay. The kinetics of adsorption was well defined by pseudo-first order and pseudo-second order kinetic models for both NO3− and HCO3−. The Fe-exchanged nano-bentonite was a better performing adsorbent of the oxyanions than Fe3O4 nanoparticles. According to the Sips isothermal model, the Fe-exchanged nano-bentonite exhibited the highest NO3− and HCO3− adsorption potential of 64.76 mg g-1 and 9.73 meq g-1, respectively, while the respective values for Fe3O4 nanoparticles were 49.90 mg g-1 and 3.07 meq g-1. Thus, inexpensiveness and easy preparation process of Fe-exchanged nano-bentonite make it attractive for NO3− and HCO3− removal from contaminated wastewater with significant environmental and economic benefits

Not Available

Not AvailableNitrate (NO3 −) and bicarbonate (HCO3 −) are harmful for the water quality and can potentially create negative impacts to aquatic organisms, crops and humans. This study deals with the removal of NO3 − and HCO3 − from contaminated wastewater using Fe-exchanged nano-bentonite and Fe3O4 nanoparticles. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, surface area measurement and particle size analysis revealed that the adsorbents fall under the nano-scale size range with high specific surface area, and Fe was successfully exchanged in the nano-bentonite clay. The kinetics of adsorption was well defined by pseudo-first order and pseudo-second order kinetic models for both NO3 − and HCO3 −. The Fe-exchanged nanobentonite was a better performing adsorbent of the oxyanions than Fe3O4 nanoparticles. According to the Sips isothermal model, the Fe-exchanged nano-bentonite exhibited the highest NO3 − and HCO3 − adsorption potential of 64.76 mg g-1 and 9.73 meq g-1, respectively, while the respective values for Fe3O4 nanoparticles were 49.90 mg g-1 and 3.07 meq g-1. Thus, inexpensiveness and easy preparation process of Fe-exchanged nanobentonite make it attractive for NO3 − and HCO3 − removal from contaminated wastewater with significant environmental and economic benefits.Not Availabl

Skewness and kurtosis of mean transverse momentum fluctuations at the LHC energies

International audienceThe first measurements of skewness and kurtosis of mean transverse momentum ($\langle p_\mathrm{T}\rangle$) fluctuations are reported in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV, Xe$-$Xe collisions at $\sqrt{s_\mathrm{NN}}$$=$ 5.44 TeV and pp collisions at $\sqrt{s} = 5.02$ TeV using the ALICE detector. The measurements are carried out as a function of system size $\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle_{|\eta|<0.5}^{1/3}$, using charged particles with transverse momentum ($p_\mathrm{T}$) and pseudorapidity ($\eta$), in the range $0.2 < p_\mathrm{T} < 3.0$ GeV/$c$ and $|\eta| < 0.8$, respectively. In Pb$-$Pb and Xe$-$Xe collisions, positive skewness is observed in the fluctuations of $\langle p_\mathrm{T}\rangle$ for all centralities, which is significantly larger than what would be expected in the scenario of independent particle emission. This positive skewness is considered a crucial consequence of the hydrodynamic evolution of the hot and dense nuclear matter created in heavy-ion collisions. Furthermore, similar observations of positive skewness for minimum bias pp collisions are also reported here. Kurtosis of $\langle p_\mathrm{T}\rangle$ fluctuations is found to be in good agreement with the kurtosis of Gaussian distribution, for most central Pb$-$Pb collisions. Hydrodynamic model calculations with MUSIC using Monte Carlo Glauber initial conditions are able to explain the measurements of both skewness and kurtosis qualitatively from semicentral to central collisions in Pb--Pb system. Color reconnection mechanism in PYTHIA8 model seems to play a pivotal role in capturing the qualitative behavior of the same measurements in pp collisions