An HVEM In situ deformation study of nickel doped with sulfur

Abstract

Intergranular embrittlement of Ni due to the segregation of sulfur to grain boundaries has been investigated in the high-voltage electron microscope by the in situ deformation technique. With sulfur segregated to the grain boundary, dislocations are effectively blocked at the grain boundary, dislocation pile-ups develop, cracks then nucleate at the intersection of the pile-ups with the grain boundary and propagate along the grain boundary. Grain-boundary cracking is not a brittle process as it is accompanied by the emission of dislocations from the crack tip. In contrast, in pure nickel the deformation proceeds across the grain boundaries and failure occurs by a ductile transgranular fracture. This promotion of intergranular failure by the presence of sulfur at grain boundaries appears to result from a decrease in the boundary cohesive strength.