A theoretical approach to the hardening mechanism of L12–Ni3Al compound with Al-rich off-stoichiometric composition was attempted based on the classical elastic interaction model between an edge dislocation and a unit cell with an equi-atomic composition embedded in Ni3Al. A tetragonal distortion was expected to arise from a local anisotropic atomic configuration in the unit cell which was recognized as a face-centered tetragonal-L10 or distorted B2 NiAl structure around an anti-site Al atom. According to the study by Cochardt et al., it was found that the maximum point force Fm on an edge dislocation from the local L10 unit cell increased with decreasing the ci/ai ratio of the L10 structure towards the stable B2 structure, which was expected from the authors’ recent electronic structure calculations on the stability of L10–NiAl relative to B2-NiAl. This increment of Fm by decreasing the ci/ai ratio accounts for a larger hardening in Al-rich Ni3Al than that in Ni-rich Ni3Al at 77K.

Effect of Tetragonal Distortion Introduced by Anti-Site Defect Configuration on Additional Hardening in Off-Stoichiometric Al-Rich Ni3Al Alloys. Miura, S., Takizawa, S., Suzuki, T., Mishima, Y., Mohri, T.: Acta Materialia, 2005, 53[19], 5175-81