Insights into cathodic hydrogen charging - surface morphology evolution

Cathodic hydrogen charging is widely used to introduce hydrogen into metals for studying hydrogen embrittlement (HE). However, its side effect on surface morphology and surface chemistry have received relatively little attention. In this study, 316L austenitic stainless steel is charged in three electrolytes: H 2 SO 4 , NaCl and NaOH solutions. The induced changes in surface morphology depend on the charging conditions and the initial surface roughness. In H 2 SO 4 , surface cracking occurs and the hydrogen content increases sharply with increasing current density. Surface roughening significantly suppresses hydrogen-induced cracking, likely due to enhanced hydrogen recombination on rougher surfaces. In contrast, charging in NaOH and NaCl does not produce surface cracking because of the relatively low hydrogen uptake. However, surface deposits originating from trace impurities in the electrolyte are observed. Among the three electrolytes, NaCl produces the least change in surface morphology. Surface cracking and deposition may influence HE behavior and should not be overlooked. • Surface roughening suppresses hydrogen uptake and surface cracking. • Hydrogen charging in H 2 SO 4 induces cracking while trace Pb in NaOH causes deposition. • Surface cracks and deposits increase hydrogen content. • Hydrogen charging in NaCl shows minimal surface effect and lowest hydrogen uptake.