Study the Effect of Chrome Coating Thickness to Fatigue Strength of the Axle-Shaped Machine Parts

Nowadays, electroplating is used in the industry to enhance the corrosion resistance, abrasion resistance of the machine elements. Chrome plating is the most widely used, especially in the dimensions restore of undersized parts. The mechanical properties of details will change when chrome plating on. There are many studies show that the chromium coating greatly affects the fatigue strength of the machine parts. In this study, the fatigue strength of the substrate (C45 steel) and chrome plated with the thicknesses of $1\theta, 3\theta, 6\theta $, and $ 9\theta $ micrometers were examined The results show that residual stress tensile and microcrack always exist in the chromium coating due to hydrogen embrittlement in the process of plating. As the coating thickness increased, the residual stress tended to decrease while the microcrack density increased Decrease in fatigue life was observed for coated specimens in comparison to base metal. Fatigue strength goes down when chromium layer thicknesses increase. $X$-ray diffraction (with Cu-Ka radiation) technique is used to determine the residual stress. Microscope optics and scanning electron microscopy (SEM) are used to evaluate the cracks of the chromium coating.