CLEAVAGE FRACTURE OF THE INTERMETALLIC COMPOUND NI3GE SINGLE-CRYSTALS

Tensile testing, optical metallography and scanning electron microfractography were examined in an attempt to resolve the fracture mechanism in the Ll2 intermetallic compound Ni3Ge at 290 K. Failure occurs in a catastrophic and brittle manner after considerable plastic deformation. River lines and cleavage steps which are characteristic of cleavage fracture are observed, but deformation twinning is not observed. The cleavage plane of Ni3Ge is {100}. The fracture stress increases with increasing the angle θ between [001] and the tensile axis, and it is well explained by a crack propagation criterion which takes account of the shear as well as the normal stress sustained by the crack and the anisotropy of Young's modulus. The cleavage fracture of Ni3Ge is considered to be related to the decrease of mobile dislocation density by a dislocation pinning mechanism based on the cube cross-slip which causes the positive temperature dependence of the yield stress. © 1979.