EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Grain boundary segregation of Cr, Cu, Mn, Mo, Ni, P and their effects on cohesion in bcc-Fe were studied by means of density functional theory simulation. Four model grain boundaries were considered in our studies: the $\Sigma$3(1$\bar{1}$1)[110], $\Sigma$3(1$\bar{1}$2)[110], $\Sigma$9(2$\bar{2}$1)[110] and $\Sigma$11(3$\bar{3}$2)[110], selected as representatives for "stacking fault", "typical coincident site lattice", and "low-angle" grain boundary types. We demonstrate that the diverse grain boundary characteristics can drastically change segregation behaviour of certain solutes, as different solutes can energetically prefer, and hence occupy different sites at the grain boundary. The effects of these solutes are presented in the framework of Rice-Wang's theory of interfacial embrittlement. We then systematically study the extent of embrittlement via segregated solutes through testing of different cleavage planes as defined by the work of separation. Finally, we performed a bond order analysis to gain a fundamental understanding the chemical bonding effects that drive such cohesion-altering effects in these grain boundaries. This study reveals that certain solutes such as Mo can have a beneficial effect on the grain boundary cohesion that spans all grain boundaries tested, while solutes such as P are strong segregants that are generally deleterious to GB cohesion.