ICAMS / Interdisciplinary Centre for Advanced Materials Simulation

Research Highlights

Ab initio study of the combined effects of alloying elements and H on grain boundary cohesion in ferritic steels

A. P. A. Subramanyam, A. Azócar Guzmán, S. Vincent, A. Hartmaier, R. Janisch.

Abstract: Hydrogen enhanced decohesion is expected to play a major role in ferritic steels, especially at grain boundaries. Here, we address the effects of some common alloying elements C, V, Cr, and Mn on the H segregation behaviour and the decohesion mechanism at a Σ5(310)[001] 36.9◦ grain boundary in bcc Fe using spin polarized density functional theory calculations. We find that V, Cr, and Mn enhance grain boundary cohesion. Furthermore, all elements have an influence on the segregation energies of the interstitial elements as well as on these elements’ impact on grain boundary cohesion. V slightly promotes segregation of the cohesion enhancing element C. However, none of the elements increase the cohesion enhancing effect of C and reduce the detrimental effect of H on interfacial cohesion at the same time. At an interface which is co-segregated with C, H, and a substitutional element, C and H show only weak interaction, and the highest work of separation is obtained when the substitute is Mn.

There are two aspects to H segregation at grain boundaries: on the one hand, the interface provides trappings sites for H and thus reduces the freely diffusing H in the microstructure. On the other hand, the trapped hydrogen can reduce grain boundary cohesion. In this study, it was investigated how the alloying elements Cr,V,Mn, and C influence these processes.