Hydrogen- enhanced decohesion mechanism of the special Sigma 5(012)[100] grain boundary in Ni with Mo and C solutes

摘要

Ni and its alloys are susceptible to hydrogen embrittlement (HE). In this work, we perform a systematic density functional theory (DFT)-based investigation on the hydrogen-enhanced decohesion (HEDE) mechanism of HE for the case of the special Sigma 5(012) grain boundary (GB) in Ni containing C and Mo impurity atoms. Segregation and co-segregation energy profiles of H along with C and Mo solute elements are investigated in detail and used to analyze the effect of Mo and C solutes on HEDE in Ni within the framework of the Rice-Thomson-Wang theory. We show that H, C, and Mo segregate to the GB in Ni. H demonstrates the GB embrittling effect while C and Mo solutes strengthen the GB in Ni. The results also show that H-Mo and H-C interactions in the bulk and at the GB are very similar and can be neglected in most of cases of co-segregation.