Microstructures, damping capacity and mechanical properties of the as-cast Fe3CrxMn2CoAl0.5 high entropy damping alloys with different Cr molar ratios

The five Fe3CrxMn2CoAl0.5 high entropy damping alloys with different Cr molar ratios were prepared by vacuum arc melting technology, and their microstructures, damping capacity, and mechanical properties were systematically investigated. The results show that as the Cr molar ratio increases, the high entropy damping alloy undergoes a microstructural transition: a single FCC phase (x = 0.5) evolves into a duplex FCC+BCC mixture (x = 0.8) and finally stabilizes as a single BCC structure (x ≥ 1.4). The FCC phase solidifies as primary dendrites, whereas the BCC phase precipitates as polygonal, equiaxed grains. Continuous FCC films wet the BCC boundaries in the Cr1.1 alloy, but this film is no longer visible in Cr1.4 and Cr2.0 alloys. Owing to the preponderance of BCC, the Cr1.1, Cr1.4 and Cr2.0 alloys exhibit significantly higher damping capacity than the FCC-dominated Cr0.5 and Cr0.8 alloys. A progressively larger absolute volumetric magnetostriction coefficient accompanies the rise in Cr content (x ≥ 1.1), while the magnetic domain morphology evolves from closed/dagger domains to fine dendritic domains, both of which amplify energy dissipation and damping. The 0.2 % compressive yield strength climbs to a maximum of 1218.3 MPa at x = 1.1 and then declines with further Cr addition. Benefiting from the exceptional ductility of the FCC matrix, the Cr0.5 and Cr0.8 alloys sustain compressive strains exceeding 60 % without fracture, attaining markedly higher compressive stresses of 2153.6 and 2640.9 MPa. Conversely, the BCC-dominated alloys (x = 1.1–2.0) suffer from intrinsic brittleness, the fracture strains decrease monotonically, while their ultimate compressive strengths fall in parallel.