Mechanical Properties of Ni3Al with Ternary Addition of Transition Metal Elements

A systematic investigation is carried out on the temperature dependence of strength in ternary Ni3Al compounds with additions of transition metal elements. The rate of solid solution hardening per one atomic percent of the solute, dσ⁄dc, is determined for each of the ternary addition using the compressive flow stress measured at liquid nitrogen temperature. It is found that dσd⁄dc can not be simply correlated with the rate of lattice parameter change, da⁄dc, although a linear correlation has been found for the addition of B-subgroup elements. The rate of change in activation energy to provide the anomalous positive temperature dependence of strength per one atomic percent of the solute, dU⁄dc, is then evaluated. Together with the results for the addition of B-subgroup elements, the apparent valence is assigned for each transition metal element by an analogy utilizing equi-valence contour determined for B-subgroup elements. Then it becomes possible to discuss the relative magnitude of the mechanical anomaly in Ni3Al in terms of the phase stability concept of L12 phase, in which e⁄a ratio as well as the atomic radius ratio of the compound, RB⁄RA, as affected by ternary addition is an important parameter to alter the stability of the phase against other geometrically close packed phases.