Trapping and diffusion in high-pressure hydrogen charged CoCrFeMnNi high entropy alloy compared to austenitic steel 316L
Michael Rhode, Jonathan Nietzke, Tobias Mente
Abstract
High entropy alloys (HEAs) have attracted considerable research attention as potential substitute materials for austenitic steels in high-pressure hydrogen environments. The corresponding hydrogen absorption, diffusion and trapping has received less scientific attention. Therefore, the CoCrFeMnNi-HEA was investigated and compared to an austenitic steel AISI 316L. Both were subjected to high-pressure hydrogen charging at 200 bar and 1000 bar. Thermal Desorption Analysis (TDA) was used to clarify the specific desorption behavior and hydrogen trapping. For this purpose, the underlying TDA spectra were analyzed in terms of a reasonable peak deconvolution into a defined number of peaks and the activation energies for the respective and predominant hydrogen trapping sites were then calculated. Both materials show comparable hydrogen diffusivity. However, there were significant differences in the absorbed hydrogen concentrations at both charging pressures. The calculated activation energies suggest strong hydrogen trapping in the CoCrFeMnNi-HEA. • First time in-depth thermal desorption analysis study of 1000 bar charged CoCrFeMnNi-HEA. • Hydrogen solubility of CoCrFeMnNi is 132 wt.-ppm (part per million) at 1000 bar. • Preferred trapping of hydrogen at Cr and Mn in HEA (atom-hydrogen-bonding). • Importance of trap occupancy rate for increase in hydrogen solubility with pressure.