Tensile properties and strengthening mechanisms of eutectic high-entropy alloys induced by heterostructure

To investigate the strengthening and deformation behavior of heterogeneous dual-phase high-entropy alloys (HEAs), AlxCoCrFeNi3 (x = 1, 1.1, 1.15, 1.2, 1.25 and 1.3) HEAs were designed and prepared. The microstructure consists of FCC phase rich in Co-Cr-Fe-Ni and BCC phase rich in NiAl, forming a soft and hard heterostructure. With the increase of Al, the microstructure changes from hypoeutectic to hypereutectic, and Al1.25CoCrFeNi3 alloy exhibits a fine eutectic lamellar morphology. Tensile results show that the strength of AlxCoCrFeNi3 HEAs tends to increase and then decrease with increasing Al elements. Al1.25CoCrFeNi3 alloy achieves the highest yield strength (535.32 MPa) and tensile strength (1060.59 MPa) as well as high plasticity (17.21%), achieving a balance of strength and plasticity. Interfacial strengthening, grain boundary strengthening, solid solution strengthening and friction stress strengthening play an important role. During the tensile process, the eutectic lamellar heterostructure results in long-range back stress, which induces the high strain hardening ability of FCC phase. Due to the continuous transformation of stress in lamellar heterostructure, the cracks initiate in BCC phase and passivate in FCC phase, which forms synergistic strengthening effects.