Design and Deformation Mechanisms of Multi-Phase Multi-Scale Eutectic Medium Entropy Alloys Cr1.5feni1.5nbx

Abstract

The design of multi-phase multi-scale eutectic high entropy alloys offers a new approach to breaking the strength-toughness trade-off in materials. However, current alloys of this type often contain precious rare metals such as Co, Ta, and Hf, and their fabrications usually involve complex procedures combining mechanical deformation and heat treatment, which hinders their engineering applications. This study established a model for designing multi-phase multi-scale eutectic medium entropy alloys based on low-cost metals and direct solidification, and developed an alloy system Cr1.5FeNi1.5NbX(X=0.4, 0.5, 0.61). Among them, the alloy Cr1.5FeNi1.5Nb0.5 was solidified with three-phase bimodal eutectic microstructure composed of nanoscale lamellar eutectic FCC/Laves and microscale irregular eutectic FCC/BCC/Laves. This effectively resolved the mutual exclusivity of strength and toughness in materials. The main reasons were as follows: Firstly, the nanoscale lamellar eutectic FCC/Laves improved the strength- toughness matching through the mechanisms including dislocation slip, crack initiation, and crack capture. Secondly, the microscale irregular eutectic FCC/BCC/Laves reduced dislocation pile-ups and alleviated stress concentration by a stepwise stress transfer mode FCC→BCC→Laves, thereby generating synergistic effects of strengthening and toughening. This study offered a novel perspective for the design and strength-toughness of multi-phase multi-scale eutectic high-entropy alloys.

Keywords: Eutectic medium entropy alloy, Multi-phase multi-scale, Mechanical properties, Deformation mechanisms