Atomic-scale investigation of deep hydrogen trapping in NbC/α-Fe semi-coherent interfaces

By Rongjian Shi, Yuan Ma, Zidong Wang, Lei Gao, Xu-Sheng Yang, L. Qiao, Xiaolu Pang. 2020

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Abstract The precipitation of niobium carbide (NbC) is a superior approach to mitigating hydrogen embrittlement (HE). The role of the semi-coherent interface between NbC and α-Fe on hydrogen trapping and HE resistance in high-strength tempered martensitic steel was investigated in this study. High-resolution transmission electron microscopy observations are performed to reveal the atomic-scale crystallographic orientation relationship, atomic arrangements, and associated crystalline defects in the NbC/α-Fe semi-coherent interface. We observed the Kurdjumov–Sachs orientation relationship with ( 1 1 ¯ 1 ¯ ) NbC / / ( 101 ) α − Fe and [ 0 1 ¯ 1 ] NbC / / [ 1 ¯ 11 ] α − Fe between the NbC and α-Fe phases. Noticeably, two sets of misfit dislocations with Burgers vectors of b ( 1 ) = a b / 2 [ 111 ] on ( 01 1 ¯ ) α-Fe planes and b ( 2 ) = a b / 2 [ 1 1 ¯ 1 ] on (110) α-Fe planes (ab is the lattice constant of α-Fe), which would be the deep hydrogen trapping sites, were characterized in the NbC/α-Fe semi-coherent diffuse interface. In addition, density functional theory-based first-principles calculations revealed that the deep binding energy between the NbC/α-Fe semi-coherent interface and hydrogen is 0.80 eV, which well matches the hydrogen desorption activation energy of 81.8 kJ/mol determined via thermal desorption spectroscopy experiments. These demonstrate that the nature of the deep hydrogen trapping sites of the NbC/α-Fe semi-coherent interface is the misfit dislocation core. Distinguished HE resistance was obtained and ascribed to the deep hydrogen trapping of uniformly dispersed NbC nanoprecipitates with an average diameter of 10.0 ± 3.3 nm. The strategy of deep hydrogen trapping in the NbC/α-Fe semi-coherent interface is beneficial for designing HE-resistant steels.

Subfields: Materials Chemistry, Mechanical Engineering, Metals and Alloys

View Paper: https://www.semanticscholar.org/paper/bb0a52b0887ba6439736f263a8ab9c82fe7a5e9f