Teh Effects Of Stress On The Properties Of Electroplated Ni And Ni-co Films On Casloom Steel

Electrodeposition is one of the most extensively applied surface techniques. However, there were few reports on the effect of stress on the deposited coatings. In this thesis, the effects of compression and tensile stress on adhesion strength, deposition rate and grain growth on electrodeposited Ni and Ni-Co films on Q235 mild steel substrate were studied. The morphology, grain size, chemical and phase compositions of the coatings were characterized by using methods of scanning electron microscopy (SEM), X-ray diffraction(XRD) and energy dispersive X-ray spectrometry (EDX), and the corrosion resistance of the coatings was evaluated by electrochemical polarization and EIS measurements in 3.5% NaCl solution and 0.5M/L H2SO4 solution.Both for the Ni and Ni-Co coatings, the hardness decreases with the increase of tensile stress, but increases with the increase of compression stress. The grain size of the coatings increases if the tensile stress increases but decreases if the compression stress increases. As compared to the pure Ni coating, hardness of nickel-cobalt coating is higher because of addition of cobalt. Both for the Ni and Ni-Co coatings, the corrosion resistance is found good if the compression stress is at higher side but in the case of tensile stress, the corrosion resistance is good if the stress is at lower side, but as compared to pure Ni coating, the corrosion resistance of nickel-cobalt coating is better because of addition of cobalt.The percentage of nickel and cobalt in Ni-Co coating increased a little, if the compression stress increases but in case of tensile stress the percentage of nickel and cobalt decreases if the tensile stress increases. It has been noticed in the SEM thickness images that both the sides of the coating has different coating thickness, and compression stress have more thickness. As compression stress increases, the coating thickness also increases. Thickness results showed that the compression stressed samples of 300,600, and 900 MPa having near about 60,90 and 150?m thickness respectively, by analyzing these thickness values it is very much clear that the optimum compression stress (900MPa) have more coating thickness as compared to others.