Mechanical Properties of Ni₃Al with Ternary Addition of B-subgroup Elements

Abstract

A systematic evaluation has been made on the magnitude of the positive temperature dependence of strength in Ni₃Al as affected by ternary additions of B-subgroup elements. The rate of change in activation energy to provide the mechanical anomaly per one atomic per cent of the solute, dU⁄dc, is determined for a variety of the ternary additions. It is shown that the larger the valence difference between the solute element and aluminum, ΔZ, the larger the dU⁄dc. Also found is that the larger the rate of lattice parameter change in the compound per one atomic percent of the solute, da⁄dc, the larger the dU⁄dC. These are well interpreted in terms of the phase stability concept to determine the relative magnitude of the mechanical anomaly in the L1₂ compounds, in which e⁄a ratio of the compound and the atomic radius ratio of the components, R_B⁄R_A, are the key factors to alter the stability of the phase against other geometrically close packed phases and thereby control the occurrence and the magnitude of the mechanical anomaly. The effect of ternary additions of B-subgroup elements on the rate of solid solution hardening per one atomic percent of the solute, dσ⁄dc is also discussed. There seems to be a linear correlation between the dσ⁄dc and the da⁄dc implying that the atomic size effect would play a major role in the solid solution hardening in Ni₃Al.