Grain boundary decohesion by sulfur segregation in ferromagnetic iron and nickel - A first-principles study

Using first-principles calculations, we simulate grain boundary decohesion (embrittlement) in ferromagnetic bee Fe Sigma 3(111)[110] and fee Ni Sigma 5(012)[100] symmetrical tilt grain boundaries by progressively adding sulfur atoms to the boundaries. We calculate the segregation energy of sulfur atom, tensile strength, and cohesive energy of the grain boundaries. We show that a certain amount of sulfur segregation (two atomic layers, 14.4 atom/nm(2)) is energetically possible to realize considering the calculated segregation energies. At this concentration, the tensile strength and the cohesive energy of the grain boundaries reduce by one order of magnitude comparing with no segregation case.