Improvement in fatigue strength of 41Cr4 steel through slide diamond burnishing

Slide burnishing (SB) is a static mechanical surface treatment based on the severe plastic deformation of the surface for which the contact between the deforming element and the surface being treated is sliding friction. SB improves the surface integrity of metal structural and machine components dramatically. This paper is devoted to improving the fatigue strength of 41Cr4 steel hourglass-shaped specimens subjected to SB with a spherical-ended deforming diamond via different combinations of basic governing parameters. Since the residual compressive stresses introduced play a significant role for the fatigue behavior of the burnished components, a comprehensive parametric study of the SB process was conducted using fully coupled thermal-stress finite element (FE) simulations. The FE model's adequacy was proven via comparison of the FE results for the residual stresses with X-ray diffraction measurements. The results obtained show that the diamond radius and the burnishing force have the strongest effects on the residual stresses, which, in turn, have a significant influence on the fatigue strength, respectively, fatigue life. An extensive experimental investigation of the effect of the selected SB basic parameters on the fatigue limit of the slide burnished specimens was carried out using Locatti's method. The latter is based on the Palmgren-Miner linear damage hypothesis, which is a particular case of a general cumulative damage theory. A planned experiment was carried out, with the governing factors changed among four levels. Regression analysis of the experimental results was carried out, and a model for predicting the fatigue limit was obtained. Based on the model obtained, a one-purpose optimization was carried out using a genetic algorithm. By means of the optimal basic parameters, the fatigue limit of the processed specimens was increased by 22.7%-from 440 to 540 MPa. The fatigue life increased more than 100 times over after SB with the optimal basic parameters.