Abstract
Lamellar eutectic structure in Al0.7CoCrFeNi high-entropy alloy (HEA) is emerging as a promising candidate for structural applications because of its high strength-ductility combination. The alloy consists of a fine-scale lamellar fcc + B2 microstructure with high flow stresses > 1300 MPa under quasi-static tensile deformation and >10% ductility. The response to shear loading was not investigated so far. This is the first report on the shear deformation of a eutectic structured HEA and effect of precipitation on shear deformation. A split-Hopkinson pressure bar (SHPB) was used to compress the hat-shaped specimens to study the local dynamic shear response of the alloy. The change in the width of shear bands with respect to precipitation and deformation rates was studied. The precipitation of L12 phase did not delay the formation of adiabatic shear bands (ASB) or affect the ASB width significantly, however, the deformed region around ASB, consisting of high density of twins in fcc phase, was reduced from 80 µm to 20 µm in the stronger precipitation strengthened condition. We observe dynamic recrystallization of grains within ASBs and local mechanical response of individual eutectic lamellae before and after shear deformation and within the shear bands was examined using nano-indentation.
Highlights
Lamellar structures exist widely in various metallic materials such as A356 aluminum alloy [1], Mg-Al-Zn magnesium alloy [2], pearlitic steel [3] and Ti-6.5 wt % Si alloy [4] and so on
In our previous work on Al0.7 CoCrFeNi alloy, we showed [9] that this dual-phase fcc and B2 (B2 with bcc nano-precipitates) and the alloy strength can be further enhanced via annealing at low temperature by the formation of coherent nano-scale L12 precipitates in the fcc phase
The current work is the first investigation of shear deformation in a eutectic high-entropy alloy (HEA) (EHEAs) and and effect of precipitation strengthening on the formation of adiabatic shear band (ASB) in any alloy
Summary
Lamellar structures exist widely in various metallic materials such as A356 aluminum alloy (eutectic Al-Si) [1], Mg-Al-Zn magnesium alloy (eutectic Mg-β-Mg17 Al12 ) [2], pearlitic steel (eutectoid cementite Fe3 C + ferrite) [3] and Ti-6.5 wt % Si alloy (eutectic Ti-Ti silicide Ti5 Si3 ) [4] and so on. Dynamic deformation often results in strain localization causing adiabatic shear band (ASB) formation. Hat-shaped specimens, commonly referred to as top hat specimens, have been widely used to study the dynamic deformation behavior under shear loading [14,15,16,17,18,19,20,21,22,23,24] using split-Hopkinson pressure bar (SHPB) apparatus. The current work is the first investigation of shear deformation in a eutectic HEAs (EHEAs) and and effect of precipitation strengthening on the formation of ASBs in any alloy. Nano-indentation results showed the change in hardness of the fcc and B2 phases before deformation and variation of hardness across the ASB.
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