Orientation and temperature dependence of a planar slip and twinning in single crystals of Al0.3CoCrFeNi high-entropy alloy

Abstract

This paper repots the effect of crystal orientation and test temperature on the tensile deformation behaviour, the type of dislocation structure (planar or cellular) and the deformation mechanism (slip and twinning) in single crystals of the fcc Al0.3CoCrFeNi (at%) high-entropy alloy. It was shown that, in the temperature range 77–573 K, the tensile deformation behaviour at 0.1% < ε < 15% along [001], [1¯11] and [011] orientations is related to the slip, at which a planar structure with dislocation pile-ups develops in the wide temperature range of 77–423 K. The planarity of the dislocation structure is determined by the strong effect of solid-solution hardening via Al atoms, since the effective radius of Al atoms exceeds the effective radii of the other elements included in the composition of the Al0.3CoCrFeNi alloy, and existence of short-range order. In slip deformation, the strain hardening coefficient in the linear stage of hardening, i.e., ΘII(T)/G(T), depends on the crystal orientation and the test temperature. In the [011]-oriented single crystals where the slip deformation develops predominantly in one system, ΘII(T)/G(T) has small values and it increases with an increasing number of active slip systems in the [1¯11]- and [001]-oriented single crystals. Twinning was detected at 77 K in the [1¯11]- and [011]-oriented single crystals after 15% and 20%, respectively. Deformation twinning in the [1¯11]- and [011]-oriented single crystals leads to an increase in ΘII(T)/G(T) and determines more complex deformation stages in the σ–ε curve in the [011]-oriented single crystals compared with the development of slip deformation at high test temperatures.