Electrodeposition of Ni-W & Ni-Mo under ultrasonication
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AbstractThe advancement of science demands materials with superior properties. Surface coating technology can be used to impart required wear or corrosion resistance on surfaces. The current research relates to the development of a deposition method for coating nanostructured Ni-W alloy and Ni-Mo alloy onto contoured external and internal surfaces of metallic components for improved corrosion and erosion resistant applications. The coatings should have a high alloy content with reproducible concentration, and should not have through thickness cracks. Electrodeposition of pure tungsten or molybdenum from an aqueous solution is not possible. However, these metals can be co-deposited along with iron group metals as an alloy. These deposits are the result of an induced co-deposition mechanism that gives an anomalous amount of W or Mo in the deposit. Ultrasonic assisted electrodeposition has been developed to give reproducible results of the chemical composition of the coating. Ultrasonication results in higher current densities during cyclic voltammetry. Increasing the deposition current density increases the tungsten content of the deposit under ultrasonicated conditions. The coatings obtained with ultrasonication show a uniform chemical composition across the thickness of the coating. Ultrasonication also minimizes hydrogen incorporation in the coatings, distributes the defect concentration more uniformly in the deposit, and promotes finer crystallite nucleation. Furthermore, ultrasonication doubles the nucleation kinetics under otherwise similar electrochemical conditions. The TEM and XRD analyses also support the nano crystallite morphology of the Ni-W deposits. The newly developed deposition method is capable of producing crack-free coatings that are nanocrystalline with high hardness, which can be used for both corrosion and wear resistant applications.