First-Principles Study on the Grain Boundary Embrittlement of Metals by Solute Segregation: Part I. Iron (Fe)-Solute (B, C, P, and S) Systems

The microscopic mechanism of grain boundary (GB) embrittlement in metals by solute segregation has been not well understood for many years. From first-principles calculations, we show here that the calculated cohesive energy (= 2.surface energy - GB energy) of bcc Fe Sigma 3(111) symmetrical tilt grain boundary (STGB) is reduced by the segregation of sulfur (S) and phosphorous (P) while it is increased by the segregation of boron (B) and carbon (C). The rate of the decrease/increase in the cohesive energy is proportional to the experimental shift in the DBTT of high-purity iron with increasing segregation. This indicates that the change in the cohesive energy of GB plays a key role in the GB embrittlement of metals.