Effect of γ′-phase particles on the orientation and temperature dependence of the mechanical behaviour of Al0.3CoCrFeNi high-entropy alloy single crystals

The present paper reports the effect of nanoscale gamma'-phase particles (d = 5-7 nm), after 50 h of ageing at 893K, on the mechanical behaviour, dislocation structure and dynamic strain ageing of the Al0.3CoCrFeNi high-entropy alloy single crystals under tensile strain, over a wide temperature range from 77 to 973K. It was found that precipitation of gamma'-phase particles leads to localization of deformation in one slip system, the development of a planar structure, a decrease in the value of (d sigma/d epsilon)/G(T) and an increase in plasticity, compared to quenched crystals, in the temperature range from 77 to 973K. The physical reason for the strain localization and the development of a planar structure in the Al0.3CoCrFeNi high-entropy alloy single crystals with gamma'-phase particles is associated with softening of the acting slip systems on shearing of particles via slip dislocations. At 973K, in the quenched single crystals and those with gamma'-phase particles of the Al0.3CoCrFeNi high-entropy alloy, dynamic strain ageing accompanied by a serrated flow on the sigma(epsilon) curves during tensile strain was observed. It was shown that at 973K, a planar structure develops simultaneously with dynamic strain ageing in quenched Al0.3CoCrFeNi high-entropy alloy single crystals. The development of a planar structure in quenched Al0.3CoCrFeNi high-entropy alloy single crystals at 973K is due to the formation of pre-precipitates which, like nanoscale gamma'-phase particles, soften the acting slip systems during the operation of the particle shearing mechanism.