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 electron microscopy (SEM). Contrary to several previous reports, no preference for {011} cleavage was found. Occasionally, fracture facets close to {115} and {117} planes were observed. For the [011] orientation, fracture 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] orientation, fracture facets exhibited similar angles but were, at the same time, close to {011} planes. In a [001] specimen, the fracture surface 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.