Nature of phosphorus embrittlement of the FeΣ3[11¯0](111) grain boundary

Abstract

Thermodynamic, electronic, and magnetic properties of the P/Fe\ensuremath{\Sigma}3[11\ifmmode\bar\else\textasciimacron\fi{}0](111) grain boundary and the P/Fe(111) free surface are compared using the full potential linearized augmented plane-wave method. The calculated segregation-energy difference of 0.8 eV is consistent with the embrittling effect of P according to the Rice-Wang thermodynamic model. The clean Fe\ensuremath{\Sigma}3[11\ifmmode\bar\else\textasciimacron\fi{}0](111) boundary is found to undergo an \ensuremath{\omega} phase transition which results in an antiferromagnetic coupling within the core of the grain boundary. Structural relaxations in the grain boundary alter the P segregation energy by \ensuremath{\sim}2.0 eV and are found to play an important role in defining the correct sign and value of the segregation energy difference controlling embrittlement. The P/Fe chemical interaction is found to be ``embeddedlike'' electrostatic rather than covalent in both environments. Long-range effects of P impurities are found for the Fe magnetization which reduce the embrittling potency of P.