Suction casting-cooling gradient mediated grain orientation in Fe2NiCoCr(VN)0.5 high-entropy alloys for strength-plasticity synergy

Abstract

This study investigates the effects of suction casting parameters on the microstructure and mechanical properties of Fe₂NiCoCr(VN)_0.5 high-entropy alloys (HEAs). By adjusting copper mold diameters (7 mm, 6 mm, 5 mm, and 4 mm), gradient cooling rates were established, linking solidification induced microstructural evolution to mechanical performance. Reducing the mold diameter (and thus increasing the cooling rate) enhances the degree of grain preferred orientation. The 5 mm sample exhibits a dual microstructure: columnar grains with [001] and [101] crystallographic orientations coexisting with equiaxed grains. Transmission electron microscopy characterization of the 5 mm alloy reveals a metastable dislocation network near the fracture zone, contributing to exceptional strength-plasticity synergy with a yield strength of 416 MPa, ultimate tensile strength of 950 MPa, and elongation of 62 %. Compared to the 7 mm alloy, the 5 mm alloy shows increases of 42.9 % in yield strength, 52 % in ultimate tensile strength, and 44.2 % in elongation. Molecular dynamics simulations demonstrate that equiaxed and columnar grains jointly govern dislocation slip behavior through multi-slip activation, enhanced dislocation storage, and regulated grain interactions. This mechanism achieves a balance between homogeneous plastic deformation and localized stress distribution. The work elucidates the role of cooling rate in microstructural evolution and establishes a framework for optimizing HEA performance through solidification parameter control.