ABSTRACT The B2 phase is a critical strengthening constituent in Al x FeCoCrNi high‐entropy alloys (HEAs), and introducing such phases onto the nanoscale cellular substructures is an ideal pathway for strengthening alloys fabricated by laser powder bed fusion (L‐PBF). However, the implementation of this strategy has been hindered by a longstanding challenge: The requisite high Al content (> 11 at%) for B2 formation often leads to severe cracking during the L‐PBF process. Here, we circumvent this challenge by employing an in situ alloying strategy to fabricate crack‐free Al x FeCoCrNi alloys with B2‐decorated cellular substructures at low Al concentrations (6.7 at% and 8.75 at%). Adjusting the content of mixed Al powders with a pre‐alloyed matrix FeCoCrNi powder enables the transition from dislocation cellular substructures (FeCoCrNi) to B2 phase‐modified substructures: particle‐like B2 in 6.70 at% Al (Al 0.3 FeCoCrNi), and banded B2 in 8.75 at% Al (Al 0.4 FeCoCrNi). The solidification model reveals the mechanism for this modulation: the Al‐rich melt between the cells solidifies into the B2 phase at the final stage. Consequently, the strengthening mechanism shifts from dislocation cellular substructure strengthening and deformation twinning to the Orowan mechanism, and then to the hetero‐deformation induced (HDI) strengthening mechanism. The strengthening model reveals that the introduction of B2‐modified cellular substructures contributes more to yield strength than that from relying solely on Al as a solid‐solution strengthening factor. This work is the first to demonstrate the crack‐free tailoring of B2‐decorated cellular substructures in L‐PBF Al x FeCoCrNi HEAs, providing a new design paradigm for regulating the microstructure and properties of other additively manufactured dual‐phase alloys.
Zhu et al. (Thu,) studied this question.