Effects of non-stoichiometry on the high-temperature deformation of Ni₂AITi

Abstract

High-temperature deformation experiments have been performed on two non-stoichiometric Ni₂AlTi compounds lying roughly on the NiAl-NiTi quasi-binary line in the Ni-Al-Ti ternary system, and the results have been compared with those for the stoichiometric compound. The marked effects of non-stoichiometry on the deformation behaviour are observed only in the Al-rich compound; the deviation from stoichiometry on the Al-rich side produces considerable strengthening of Ni₂AlTi and causes the 〈110→ 〈001〉 slip mode transition in crystals with orientations near [111]. In crystals of the Ti-rich compound and in those of the Al-rich compound with orientations away from [111], slip occurs along 〈110〉 directions, as in the stoichiometric compound.

The 〈001〉 superlattice dislocations in the Al-rich compound are found to be dissociated into two 1/2〈001〉 superlattice partial dislocations coupled by a ribbon of antiphase boundaries (APB). From the separation of the superlattice partial dislocations, the energy of the APB on {110} in the Al-rich compound is found to be about 115 mjm ⁻². Assuming that the excess AI atoms in the Al-rich compound are all on the Ti-sublattice, the energy of the APB for the stoichiometric composition is estimated to be higher than 155mJm⁻².