The Influence of Ti and Al on the Evolution of Microstructure and Mechanical Properties in Medium-Entropy and High-Entropy Alloys Based on AlxTixCrFe2Ni2

This study focuses on the cobalt-free medium-to-high-entropy alloys Al_xCrFe₂Ni₂ and Al_xTi_xCrFe₂Ni₂, investigating the influence of Al_x and Ti_x (where x = 0.2, 0.3, 0.4, 0.5, and 0.6) on the development of microstructural and mechanical properties in as-cast and annealed states. Structural changes were examined using optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) measurements, while mechanical properties were evaluated through Vickers hardness testing and compression testing. X-ray diffraction analysis of the Al_xCrFe₂Ni₂ alloys confirmed that increasing the Al content in the as-cast state leads to the formation of a BCC phase, which completely dissolves into the FCC matrix after homogenization annealing. These single-phase alloys exhibit good ductility with relatively high strain hardening, such as the Al_0.6CrFe₂Ni₂ alloy, which achieved a maximum compressive strength of σmax=1511 MPa at 50% deformation. A significant strengthening effect of Ti was observed in the Al_xTi_xCrFe₂Ni₂ alloys, the mechanical properties of which are closely linked to the higher BCC phase content in the homogenized structure. The highest compressive strength, σmax=2239 MPa, was achieved by the Al_0.5Ti_0.5CrFe₂Ni₂ alloy, which fractured via a transcrystalline brittle fracture at 43% deformation. All alloys investigated offer an excellent balance between strength and ductility, which could meet the requirements of demanding structural applications.