Enhanced strength-ductility synergy of an AlCoCrFeNi2.1 eutectic high entropy alloy by ultrasonic vibration

Abstract

The mechanical properties of eutectic high entropy alloys (EHEAs) can be significantly improved by adjusting its microstructure; however, the conventional adjustment approaches are inefficient and trapped in a strength-ductility tradeoff. In this study, we applied a compressive stress of 350 MPa (about 60 % yield strength) with ultrasonic vibration of 20 kHz frequency and 20 μm amplitude on an AlCoCrFeNi2.1 EHEA for different processing time. The ultimate tensile strength and total elongation of the EHEA were prominently enhanced to 1050 MPa and 27.4 % after 20 min ultrasonic processing, representing an increment of 17 % and 54 % from the initial state (900 MPa and 17.8 %), realizing the synergistic enhancement of both strength and ductility. The structural analysis of the ultrasonically processed AlCoCrFeNi2.1 EHEA shows that the strengthening effect induced by BCC(B2) precipitates with a typical size of 1 μm provoked by ultrasonic vibration was the primary reason for the enhanced strength. The synchronous deformation of alternating soft FCC(L12) phase and hard BCC(B2) phase as well as the motivated multiple slip systems intensified the strain hardening effect, resulting in the improvement of strength-ductility synergy. This study provided a new and efficient way to overcome the strength-ductility tradeoff and prepare a EHEAs with high mechanical properties.