Fatigue strength of chromium coated elements and possibility of its improvement with slide diamond burnishing

Surface layer condition and fatigue strength of chromium coated elements were tested. Special shape samples cut out of chromium coated shafts were symmetrically deflected on electrodynamic vibrator at sample frequency oscillations in the 1000 Hz order. They were 42CrMo4 and 41Cr4 steel samples with a 25 and 50 μm chromium coat finished by slide diamond burnishing and polishing. Surface topology parametres, surface microhardness and residual stresses in the surface layer were checked and fatigue strength was tested. Before the coating was applied, the roller surfaces of the samples were ground and band polished. It was found that chromium electroplating causes detrimental, tensile stresses in the surface layer and worsens the fatigue strength limit. Slide burnishing of chromium coatings produces advantageous, compressive stress in the surface layer and the oscillatory bending fatigue strength of elements with burnished coatings can be improved up to 40%, which completely reduces the detrimental chromium plating effects. It can also be stated that slide burnishing of coatings does not create bigger technical problems and gives better results than band polishing.