Study by EELS of helium bubbles in a martensitic steel

This work presents measurements of the helium density and pressure in small bubbles in a martensitic steel, which is a vital first step towards identifying their role in the microstructural mechanisms determining the macroscopic properties of the material. Electron Energy-Loss Spectroscopy in the Scanning Transmission Electron Microscope has been used to analyse individual bubbles. The energy shift of the 1s → 2p transition and the helium density have been measured for each bubble analysed. The pressure inside the bubbles has been calculated from the helium density using an equation of state. In these bubbles, the values for the helium pressure seem to be smaller than the equilibrium pressure, and agree in trend with the findings of previous studies, although our results extend to smaller radii and higher pressures.