An atomic study on the phase transformation behavior of laser powder bed fusion of Fe-riched high-entropy alloy at cryogenic temperature

• Compression behavior of the LPBF of Fe 60 (CoCrNiMn) 40 are highly sensitive to temperature. • Element segregation in cellular substructure and reduced SFEs are responsible for the TRIP behavior. • The continuous slip of Shockley partial dislocation is the main reason for the formation of HCP phase. • Dislocation reaction and HCP phase obstruction are the sources of work hardening. Laser powder bed fusion (LPBF) induces microstructural and compositional heterogeneities that can critically affect the deformation behaviors and mechanisms. In this study, heterogeneous Fe 60 (CoCrNiMn) 40 was fabricated via LPBF of mixed pure Fe and FeCoCrNiMn powders. Compression tests were subsequently performed under varying temperatures and strain rates. The result indicates that the TRIP effect mediated by FCC-to-HCP phase transformation was activated at 77 K, while deformation twins (DTs) dominate the plastic deformation at 298 K. Furthermore, molecular dynamics (MD) simulations reveal that the HCP phase originates from successive gliding of Shockley partial dislocations, and eventually resulting in the unusual structure containing both DTs and HCP phase, which shows excellent agreement with experimental observations. The reduced stacking fault energy (SFE) at lower temperatures promotes the multiplication of Shockley partial dislocations, which subsequently evolve into Lomer-Cottrell locks, Hirth locks and Frank partial dislocations. Dislocation entanglement and HCP phase-induced dislocation obstruction collectively enhance yield strength and strain hardening capacity at cryogenic temperatures. The results of this study help to provide new insights into the TRIP effect of low SFE alloys fabricated by LPBF.