Abstract
Hydrogen embrittlement is often a catastrophic phenomenon of machine elements failure under cyclic stresses. This hydrogen is generated as a result of tribo-chemical and mechanical actions on the working surfaces. This hydrogen can have three different zones or stages of behaviour under tribo-mechanical actions. Firstly, it can strongly adsorb on the mating surfaces at a shallow subsurface zone and take up the load in the boundary-lubricating regime and reduce the coefficient of friction. At a second stage, it can diffuse to the deep subsurface zone where it might work together with Hertzian stresses and embrittle the subsurface zone. The last zone of hydrogen activity is the bulk of the bearing steel where it is known to collect under the action of tensile stresses and degrade the bearing steel and hence resulting in catastrophic failure. It is important and interesting to follow up the presence of hydrogen in these zones in order to predict the safe functioning of the machine elements. In addition to this a clear distinction must be made between the internal hydrogen embrittlement and environmental hydrogen embrittlement. Two important behaviours of hydrogen are studied and quantification was made by a melting sample technique. Dependence of hydrogen diffusion on the variation of tribo-mechanical action is shown in this work. This was done by studying the pure rotating bending, rotating bending with combination of sliding and rolling motion of the mating surfaces and uni-axial tensile experiments in pure water environment to see the diffusion of hydrogen into or out of the AISI-52100 bearing steel and in silver steel. Two different approaches were adopted in order to investigate the presence of hydrogen in three zones under the action of different stress states. The two techniques are melting sample technique by using hydrogen analyser and elastic recoil detection analysis, an ion beam technique. It is believed until now that hydrogen spread is homogeneous in the bearing steel. The results obtained showed that the inherent amount of hydrogen in steel samples is non-homogeneous and it was learnt that inherent amount of hydrogen in the steel samples is very important in order to support the boundary lubrication by hydrogen. Content of hydrogen in the steel samples showed a relation to the increasing number of cyclic stresses. The sliding–rotating bending stress state showed a considerable wear of the surfaces but the content of hydrogen was not very high in that sample when compared to the samples that were run under pure rotating bending stress state.