FRACTURE MORPHOLOGY OF NIAL SINGLE-CRYSTALS TESTED IN TENSION

The fracture surfaces of NiAl single crystals, strained to fracture in uniaxial tension at room temperature, were analyzed by scanning elect ron microscopy (SEM). Contrary to several previous reports, no prefere nce for {011} cleavage was found. Occasionally, fracture facets close to {115} and {117} planes were observed. For the [011] orientation, fr acture tended to occur at a 45 deg angle to the tensile axis (i.e., in the direction of maximum shear stress). In the case of the [111] orie ntation, fracture facets exhibited similar angles but were, at the sam e time, close to {011} planes. In a [001] specimen, the fracture surfa ce normals tended to include an angle close to 35 deg with the tensile axis. This suggests that the tensile fracture of [001] crystals could be associated with [111]{112} slip.