X-Ray Examination of Brittle Fractures in Extruded Chromium

Abstract

X-ray examinations of brittle fractures in polycrystalline chromium, produced at temperatures between 193°K and 623°K, have been made. Estimates of the amount of deformation present at the fracture surfaces showed that very large plastic strains were associated with brittle cleavage fracture at the higher temperatures, such that the length of a self-sustaining crack calculated according to the modified Griffith crack formula of Hall, was more than an order greater than the mean grain diameter of the material. Plastic strains of this order would be expected to result in ductile behavior. It is suggested that brittle failure was caused by the presence of a fine dispersion of precipitate particles, which delayed the action of cross slip in sealing off the early stages of cracking. The spacing of the precipitate particles was estimated to be between 6000 and 7000 A.