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The current work investigates the effects of variation of coating bath temperature on friction and wear behaviour of electroless Ni–B (ENB) coatings developed from stabilizer free bath. Coating is applied to specimens made up of AISI 1040 steel. Coatings were deposited at three different coating bath temperatures (85°C, 90°C and 95°C). Field emission scanning electron microscopy, inductively coupled plasma-optical emission spectrometer, and X-ray diffraction were used to characterize the coating for surface morphology, chemical composition, and phase structure respectively. Pin-on-disc tribo-tester was used to estimate the friction and wear behaviour of ENB coatings at room temperature (25ºC), 100ºC, 200ºC and 300ºC. The coefficient of friction was higher at high temperature due to higher roughness of the coatings obtained from stabilizer free bath, adhesion and ploughing. The wear rate at 200°C or 300°C was lower compared to 100°C. Additionally, the ENB coatings were subjected to thermogravimetric analysis which reveals higher thermal stability of coatings obtained at 95°C. A scratch tester at constant (6 N) and progressive load (5-24 N) was used to estimate the coatings scratch hardness and adhesion. The corrosion behaviour of ENB coatings in 3.5 % NaCl was studied using potentiodynamic polarization tests. The Ni-B coated specimens could efficiently provide barrier protection to steel substrate. But the corrosion potential was lower compared to lead stabilized bath.

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The present study considers the tribological behavior and corrosion resistance of electroless Ni-B-W coatings deposited on AISI 1040 steel substrates. Coating is characterized using scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction technique. In as-deposited condition, coatings are found to be amorphous. On heat treatment, precipitation of crystalline Ni (1 1 1) and its borides take place. For as-deposited coating, the microhardness is obtained as [Formula: see text]759[Formula: see text]HV[Formula: see text] which increases to [Formula: see text]1181[Formula: see text]HV[Formula: see text] and [Formula: see text]1098[Formula: see text]HV[Formula: see text] when heat treated at 350[Formula: see text]C and 450[Formula: see text]C, respectively. Incorporation of W in Ni-B coating results in an increase of hardness by 89[Formula: see text]HV[Formula: see text] in as-deposited condition. Heat treatment also results in increase in crystallite size of Ni (1 1 1). Wear rate and coefficient of friction (COF) of the coatings are evaluated on a pin-on-disc setup under both dry and lubricated sliding conditions. Wear resistance is observed to improve on heat treatment with an increase in crystallite size while COF deteriorates. However, in as-deposited condition, wear rate and COF of Ni-B-W coatings improve by [Formula: see text]5 and [Formula: see text]3 times, respectively, compared with Ni-B coatings. Wear and friction performance of the coatings are enhanced under lubrication due to the columnar structure of the coatings that retain lubricants. Corrosion resistance of Ni-B-W coating in 3.5% NaCl solution gets improved on heat treatment.

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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.

Electroless nickel coatings containing Mo possess higher thermal stability in comparison with the binary alloy variants. In a quest to achieve enhanced thermal stability of Ni–B coatings, Mo is incorporated to obtain a ternary Ni–B–Mo coating. The coatings are deposited on AISI 1040 steel and characterized using energy dispersive X-ray (EDX) analysis, X-ray diffraction method and scanning electron microscope. The coatings are observed to lie in the mid-B range with amorphous structure in as-deposited condition. On heat treatment, precipitation of crystalline Ni and its borides is observed. The typical cauliflower-like surface morphology of the deposits could be observed in scanning electron micrographs. Microhardness measurements reveal the enhanced thermal stability of Ni–B–Mo coatings. Tribological behavior of Ni–B–Mo coatings at room and elevated temperatures (100∘C, 300∘C and 500∘C) is observed on a pin-on-disc type tribo-tester by varying the applied normal load (10–50[Formula: see text]N) and rotational speed of the counterface disc (60–100[Formula: see text]rpm). The purpose of the present work is to observe the tribological behavior and associated tribo-mechanisms at different temperatures under dry sliding condition. In general, the wear of the coatings increases with an increase in applied normal load and speed at room temperature, 100∘C and 300∘C. At 500∘C, the wear increases with load but with speed it first increases up to 80[Formula: see text]rpm and then decreases. The COF does not show a similar behavior like the wear with varying load and speed at different temperatures. Instead, it is controlled by the accompanying wear mechanisms, formation of oxide debris and oxide layers of Ni and Mo. The worn surface of the coatings is examined using scanning electron microscope and EDX analysis. Back scattered images of wear tracks of Ni–B–Mo coatings at the highest levels of load (50[Formula: see text]N) and speed (100[Formula: see text]rpm) at different temperatures further reveal the oxide formation and tribochemical reactions.