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 AlxCrFe2Ni2 and AlxTixCrFe2Ni2, investigating the influence of Alx and Tix (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 AlxCrFe2Ni2 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 Al0.6CrFe2Ni2 alloy, which achieved a maximum compressive strength of σmax=1511 MPa at 50% deformation. A significant strengthening effect of Ti was observed in the AlxTixCrFe2Ni2 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 Al0.5Ti0.5CrFe2Ni2 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.