The influence of hydrogenation on propagation of surface acoustic waves in structural steel with nanocrystalline layer

The influence of the surface layer with nanocrystalline structure (NCS), electrolytical hydrogen charging with different intensities and their complex effect on the velocity of surface acoustic waves (SAW) was studied on the 40X steel. Changes in the NCS parameters under hydrogen action were revealed. Using SAW with frequencies of 1; 3 and 6 MHz, the distribution of properties through the surface layer thickness was estima­ted. A decrease in the SAW velocity is shown for the layer with NCS versus the matrix metal, as well as for the hydrogen charged metal versus the non-hydrogenated one. A non-monotonic de­pen­dence of the change in SAW velocity on the hydrogen charging intensity of the steel was established. The dependence of the SAW velocity on the frequency was observed for the hydrogen charged steel, thus indicating a non-homogeneous distribution of changes in properties through the depth. The surface NCS layer is a barrier for the hydrogen permea­tion into the steel depth under hydrogen charging at ic = 0.1 mA/cm2