Mechanical response and plastic deformation in single- and dual-phase polycrystalline FeNiAl alloys: molecular dynamics analysis

This study compares the tensile properties of single-phase and dual-phase polycrystalline FeNiAl alloys using molecular dynamics (MD) simulation. The findings reveal that dual-phase polycrystalline materials, incorporating both B2-NiAl and face-centered cubic (FCC)-Fe phases, exhibit significantly superior strength and strain hardening compared to their single-phase FCC-FeNiAl counterparts. The back stress and Bauschinger effect emerge as pivotal factors in strengthening and strain hardening during the tensile deformation of dual-phase polycrystalline materials. In single-phase polycrystalline materials, grain plastic deformation is uniform, primarily driven by Shockley partial dislocation \(b=\frac{1}{6}<121>\) $b=\frac{1}{6}<121>$ . Additionally, deformation twinning is observed with increasing strain. Conversely, in dual-phase polycrystalline materials, non-uniform plastic deformation occurs because of differences in crystal structure between the two phases. Plastic deformation predominantly takes place in the soft domain FCC-Fe grains, while dislocations encounter hindrance from the hard domain B2-NiAl grains, leading to the generation of back stress. The direction of dislocation movement opposes the back stress, further impeding plastic deformation and enhancing material strength. In cases where the back stress is sufficiently high, the dislocation source may halt dislocation emission, creating significant stress concentration between soft and hard domains, consequently causing local stress and strain and ultimately leading to crack formation. The comprehension of these mechanisms provides a valuable reference for developing FeNiAl alloys with exceptional mechanical properties.