Ductilizing B2 for high strength-ductility synergy in precipitation-strengthened FCC/B2 dual-phase HEAs at 650 °C

Abstract

Designing precipitation-strengthened FCC/B2 dual-phase high-entropy alloys (HEAs) is an effective method for preparing structural materials with superior strength and lower density at elevated temperatures. However, high-density precipitates in FCC/B2 dual-phase HEAs will also cause a sudden drop in ductility, especially for the B2 phase with insufficient slip systems. Here, by tailoring the precipitates of disordered FCC and ordered L1₂ in the B2 phase, we achieved significant ductilization of the B2 phase. With the ductilized B2 phase, the precipitation-strengthened FCC/B2 dual-phase HEAs exhibited superior strength-ductility synergy over a wide temperature range. At 650 °C, it was different from traditional understanding that the hard L1₂ precipitate improved the deformability of B2 via sustainable stacking fault shearing, whereas the soft FCC precipitate transformed into the hard 18 R phase which reduced the B2 ductility by suppressing the dislocation motion of the B2 phase. By tailoring the precipitates in the B2 phase from FCC to L1₂, the strain localization near the FCC/B2 phase boundary was significantly decreased and premature cracking was inhibited, leading to the superior ductility. These findings advance the microstructural design of precipitation-strengthened FCC/B2 dual-phase HEAs by introducing hard yet ductile precipitates to the B2 phase to enhance ductility, shedding light on the development of alloys with exceptional mechanical properties and lower density at elevated temperatures.