Application of the selected area channeling pattern method to the study of intergranular fracture in Ni 3Al

Abstract

The selected area channeling pattern method was applied to the characterization of grain boundaries on the basis of the coincidence lattice site model and to the detection of plastic strain accompanying intergranular fracture in cast or recrystallized Ll 2type Ni 3Al and Ni 3(Al, Ti) polycrystals. The sum of the numbers of low angle and twin (Σ3) boundaries observed was less than 20% of the number of all boundaries studied. An evident resistivity of low angle and Σ3 boundaries against intergranular cracking was found. The boundaries of grains having the coincidence orientation relation (Σ5-Σ29) and random boundaries were preferentially broken under tensile stress. The amount of plastic strain accompanying intergranular fracture of Ni 3Al was found to depend upon processing conditions (as-cast or as-recrystallized state), deformation temperature, and substitution of titanium for aluminum. It is pointed out that the amount of plastic strain is consistently larger in materials having higher resistivity against intergranular cracking.