In-situ-determination of tribologically induced hydrogen permeation using electrochemical methods

Abstract

White etching cracks are one of the possible causes of bearing damage, which can lead to the failure of wind turbines. The mechanisms of hydrogen diffusion in bearings are not yet fully understood, but it is assumed under tribological loading that the lubricant degradation releases hydrogen which diffuses into the contacting surfaces (i.e. steel). This leads to hydrogen-induced cracking and damage to the bearings. In order to better understand these mechanisms, it is necessary to investigate the influence of tribological loads and lubricant composition on hydrogen release. For this purpose, a test setup was developed for the analysis of tribologically induced hydrogen permeation by means of a ball-on-plate test. The diffused hydrogen was measured with an electrochemical three-electrode setup. The results showed a direct correlation between the amount of hydrogen released and the applied normal load. Furthermore, an increased velocity resulted in enhanced diffusion of hydrogen through metal. In addition, the tribological contact surface was decisive for hydrogen permeation. The higher velocity and the larger contact area result in an activated nascent iron surface which promotes hydrogen penetration. The results show that lubricants can be classified as critical for the formation of hydrogen embrittlement in tribological contacts.