First-principles study on the grain boundary embrittlement of metals by solute segregation, 1; Iron(Fe)-Solute(B, C, P, and S) systems

溶質元素の偏析による粒界脆化の第一原理計算による研究,1; Fe-B,C,P,S系

山口 正剛   

Yamaguchi, Masatake

The microscopic mechanism of grain boundary 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 (= surface energy - grain boundary energy) of bcc Fe 3(111) symmetrical tilt grain boundary is reduced by the segregation of sulfur and phosphorous, while it is increased by the segregation of boron and carbon. The rate of the decrease/increase in the cohesive energy was excellently proportional to the experimental shift in the ductile-to-brittle transition temperature of high-purity iron with increasing segregation. It indicates that the change in the cohesive energy of grain boundary plays a key role in the grain boundary embrittlement.