Effect of heterogeneous solute distribution on the anomalous thermomechanical response of Cu–Ni alloy single crystals below 50 K

The anomalous temperature dependence of the critical resolved shear stress (CRSS) of Cu–Ni alloys observed below a certain temperature, T o = 50 K, has been accounted for by introducing a stress-concentration factor f(T) = [(T ′ + T o)/(T ′ + T)] in the monotonic CRSS–T formulation of the kink-pair nucleation model of solid-solution hardening. The empirical constant T ′ is found to depend not only on the solute concentration, c, but also on the nature of the solute distribution in the host lattice. It is found that the solute distribution is random for c ≤ 14 at.% Ni in the Cu lattice and for c ≤ 20 at.% Cu in the Ni lattice, whereas some sort of local ordering occurs for all other values of solute concentration.