The effect of nonstoichiometry on the positive temperature dependence of strength of Ni3AI and Ni3Ga

Compression tests have been carried out on the polycrystalline Ni₃Al and Ni₃Ga alloys over the temperature range 77 ~ 1000 K. The flow stress and the temperature dependence of strength are found to be sensitive to small composition change within the phase field. The anomalous strengthening of these compounds with temperature is more significant for Al-and Ga-rich deviations than for Ni-rich deviations from stoichiometry. The change in activation constant of these compounds derived from the flow stress increment appears to be discontinuous at the stoichiometric composition. The influence of deviations from stoichiometry on the temperature dependence of strength could be accounted for by the phase stability concept proposed by the present authors. It is concluded that the phase stability of the Ni₃Al and Ni₃Ga alloys with respect to the D0₂₂ phase as well as the D0₁₉ phase are reduced as the composition of the minority component is increased. This change leads to the relatively reduced {100} antiphase boundary energy which increases the propensity for the cross slip onto cube plane. formerly graduate student, Department of Material Science and Engineering, Tokyo Institute of Technology.