Hydrogen trapping behavior in IVB-VB transition metal carbides

The hydrogen capture mechanism of transition metal carbides is crucial to improve the hydrogen embrittlement resistance of steel materials. Although numerous experimental and theoretical studies have been carried out, the mechanism of hydrogen capture in these carbides has not been fully elucidated. In this paper, the ability of transition metal carbides (TMCs; TM=Ti, Zr, Hf, V, Nb and Ta) to capture hydrogen is studied by first-principles calculations. It is found that there is a strong correlation between the hydrogen solubility energy and the number of valence electrons of IV-VB transition metal carbides. With the increase of the number of valence electrons, the hydrogen solubility energy decreases, which indicates that IVB transition metal carbides have strong hydrogen capture ability. Compared with interstitial sites, the mechanism by which carbon vacancies are more stable hydrogen capture sites is to enhance the capture stability of hydrogen atoms by reducing the effect of chemical and mechanical effects on the dissolution energy of hydrogen atoms. In the interstitial site, hydrogen atoms tend to occupy the triangular site (TMCs-TM) surrounded by three transition metal atoms and one carbon atom. The bonding interaction between the hydrogen atom and the nearest carbon atom is the main factor affecting the stability of hydrogen atom capture.