Tailoring deformation mechanism via Ti, V, Mo microalloying in L-PBF fabricated Fe50Mn30Co10Cr10 multi-principal element alloys for enhanced strength-ductility synergy at room and cryogenic temperatures

초록

A dual-phase Fe50Mn30Co10Cr10 multi-principal element alloy (MPEA), composed of gamma (FCC) and epsilon (HCP) phases, exhibits a favorable balance of strength and ductility through the activation of transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) mechanisms. In this study, a modified alloy (M-MPEA) was developed by incorporating 0.1 at.% each of Ti, V, and Mo, aiming to further enhance plasticity via stacking fault energy (SFE) control. Alloys were fabricated via laser powder bed fusion (L-PBF), where rapid solidification promotes refined microstructures that synergize with minor-element alloying. Tensile tests conducted at 298 K and 77 K revealed that the base MPEA exhibited ultimate tensile strengths (UTS) of 769.2 MPa at 298 K and 1175.2 MPa at 77 K, with elongations of 28.8 % and 21.4 %, respectively. In contrast, the M-MPEA demonstrated comparable strengths of 773.3 MPa and 1199.7 MPa, but significantly improved elongations of 37.8 % and 27.2 % at each temperature. Post-deformation EBSD analysis revealed more pronounced gamma ->epsilon phase transformation and active twinning within the epsilon phase in the M-MPEA, indicating the concurrent operation of TRIP and TWIP. The addition of minor alloying elements is inferred to have reduced the effective SFE, thereby facilitating stable phase transformation and uniform strain distribution, which ultimately alleviates the conventional strength-ductility trade-off. These findings highlight minor-element alloying as a cost-effective and practical strategy to exploit the intrinsic advantages of L-PBF, providing a robust pathway to tailor deformation mechanisms and optimize the cryogenic performance of MPEAs.

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