Influence of partial substitution of Cr by Al on microstructure and mechanical behavior of Fe30Ni35Cr35 multi-principal element alloy

Influence of partial substitution of Cr by Al on microstructure and mechanical behavior of Fe30Ni35Cr35 multi-principal element alloy (MPEA) was investigated. In detail, Co-free Fe30Ni35Cr(35-x)Alx (x = 10, 12.5, 13.75 and 15 at.%) MPEAs were prepared by a vacuum arc melting process, subsequently, microstructure and tensile properties of these MPEAs were carefully studied. The as-cast Fe30Ni35Cr(35-x)Alx alloys are composed of face-centered cubic (FCC) and body-centered cubic (BCC) phases with spherical B2 nano-precipitates embedded in the BCC phase and B2 lamellar structure surrounding the BCC phase simultaneously. In particular, Al content strongly influences the solidification process of these alloys; with increasing Al content, the initial morphology varied from columnar dendritic grains (10 < x < 13.75) to equiaxed grains with Widmanstätten structures (x = 15) and resulted in increased tensile strength and hardness with reduced ductility. The as-cast Fe30Ni35Cr21.25Al13.75 alloy exhibits the best mechanical properties in Fe30Ni35Cr(35-x)Alx alloys with an ultimate tensile strength (UTS) of ∼1111.8 ± 11.4 MPa and a total elongation of ∼20.7 ± 2.1%. Furthermore, our study demonstrates outstanding combinations of ductility and strength in multi-phase MPEAs, ascribing to various complementary strengthening mechanisms, such as hetero-deformation induced (HDI) hardening and precipitation strengthening, which influence the work hardening and dislocation movement at different tensile strains.