First-principles study of boron segregation in fcc-Fe grain boundaries and its influence on interface adhesive strength

Abstract

Boron, a commonly used microalloying element in steel, is distributed mainly at the grain boundary of stainless steel and plays an important role in regulating the mechanical, corrosion resistance and grain boundary structure of stainless steel. Owing to the small amount of boron added into the steel, it is difficult experimentally to detect the traces of boron segregation at the grain boundary, not to mention analyzing the structural characteristics of the boron segregation grain boundary. First-principles density functional theory (DFT) provides convenience in analyzing the existence mode and mechanism of boron in austenitic steel from the atomic level. Combining with the actual grain boundary structure types in austenitic stainless steel, Fcc-Fe Σ3(112), Σ5(210), Σ5(310), Σ9(114), Σ9(221) and Σ11(113) symmetric tilt grain boundaries are constructed based on DFT, and the segregation behaviors of boron atoms at the six grain boundaries are studied to reveal the segregation mechanism from the atomic and electronic level. The results show that boron segregation occurs mostly at Σ5(210), Σ5(310) and Σ9(114) grain boundaries, while a relatively weak segregation tendency is observed at Σ9(221), Σ3(112) and Σ11(113) grain boundaries; boron atom preferentially occupies the pentahedral or hexahedral segregation position with the largest coordination number; the interface adhesive strength at grain boundaries is improved by the segregation of boron according to the tensile test, which complies with the calculation results of Rice-Wang thermodynamic model; the chemical effect caused by the increase of local charge density after boron segregation at Σ9(114) grain boundary outstrips the adverse effect of structural changes, and the strong interaction between B-p electrons and Fe-s electrons improves the interface adhesive strength. The results provide a reference for using boron to optimize the interface structure of austenitic stainless-steel.