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Electroless nickel-phosphorous (Ni P) coating was deposited on steel substrate followed by annealing at 600 °C in an argon atmosphere. Nanoindentations and nanoscratch experiments were performed on the as-deposited and annealed coating. Improvement of 32% in hardness was found on annealing the coating, which might be due to the two major phenomena. Firstly, presence of Ni 3 P precipitates which accelerated the bowing of dislocations and observed to be the dominant mechanism in increased hardness. Secondly, diffusion of iron (Fe) and chromium (Cr) atoms from the substrate to the coating. Scherrer technique and TEM analysis showed the increase in Ni grain size on annealing. Annealed coating showed an enhancement of 31% in elastic modulus compared to as-deposited coating. Increased elastic modulus could be due to the reduction in triple junction and grain boundary as a result of increased grain size. Strain hardening exponent was found higher for annealed coating (0.33) compared to as-deposited coating (0.25) indicating lower pile-up formation in annealed coating during indentation. Higher scratch hardness resulted lower scratch width and depth for the annealed coating. Coefficient of friction decreased from 0.30 for as-deposited coating to 0.23 for annealed coating, resulting 58% reduction in calculated wear rate of the scratch of annealed coating. Direct correlation was observed between nanoindentation and nanoscratch results of as-deposited and annealed Ni P coatings. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) reinforced nickel–tungsten (Ni–W) coatings were successfully fabricated on steel substrate by pulse electrodeposition method (PED) and the amount of SiC was varied as 0 g/l, 2 g/l, and 5 g/l in Ni–W coating. Effect of subsequent addition of SiC on microstructures, phases and on corrosion property of the coating was investigated. Field emission scanning electron microscopy (FE-SEM) image of the surface morphology of the coating showed the transformation from the dome like structure to turtle shell like structure. X-ray diffraction (XRD) of Ni–W–5 g/l SiC showed the disappearance of (220) plane of Ni(W), peak splitting in major peak of Ni(W) and formation of distinct peak of W(Ni) solid solution. Absence of (220) plane, peak splitting and presence of W(Ni) solid solution was explained by the high resolution transmission electron microscopy (HR-TEM) images. Tafel polarization plot was used to study the corrosion property of the coatings in 0.5 M NaCl solution. Ni–W–5 g/l SiC coating was showed higher corrosion resistance (i.e. ∼21% increase in corrosion potential, E corr ) compared to Ni–W coating. Two simultaneous phenomena have been identified for the enhanced corrosion resistance of Ni–W–5 g/l SiC coating. (a) Presence of crystallographic texture (b) formation of continuous double barrier layer of NiWO 4 and SiO 2 . [ABSTRACT FROM AUTHOR]