Hydrogen-enhanced entropy (HEENT): A concept for hydrogen embrittlement prediction

The concept of hydrogen-enhanced entropy (HEENT) for hydrogen embrittlement prediction was firstly introduced and discussed through experimental validation methods, multiscale characterization, and trapping studies. The accumulated generated entropy reaches a constant value (fatigue fracture entropy (FFE)) regardless of hydrogen content. Hydrogen-enhanced localized plasticity (HELP) is the dominant mechanism for hydrogenassisted cracking in the studied material, due to quasi-cleavage fracture pattern with serrated marking and Henhanced planar slip. Fatigue life is reduced due to increasing hydrogen uptake with increasing current density of H charge, and the accumulated generated entropy reaches a constant FFE value. As H content increases, a fraction of weakly trapped hydrogen at interstitials and dislocations in the ferrite increases, and the possibility of reaching hydrogen to crack tip and slip planes increases. Direct evidence of HELP mechanisms with a welldeveloped dislocation substructure is reported for the first time in pearlitic steels with nanoscale observations near the H-assisted crack path. The contribution of microplasticity due to the HELP mechanism to the total entropy compensates for the total entropy reduction generated due to reduced fatigue life. This introduces the hydrogen-enhanced entropy (HEENT) concept for hydrogen embrittlement prediction.