Thermal modification of brittle CoFeNi2(Ti3Si5)0.16 eutectic high-entropy alloy by annealing treatment

Adopting the idea of thermal modification of conventional Si-containing eutectic alloys, this study performed heating of the brittle CoFeNi2(Ti3Si5)(0.16) eutectic high-entropy alloy under various annealing conditions to attempt the fragmentation and spheroidization of eutectic microstructure and improve fracture plasticity. Results reveal that the as-cast alloy exhibited fine eutectic microstructures with lamellar + network morphologies, consisting of face-centered cubic (FCC) and M16Ti6Si7-type silicide. After annealing at 1100 degrees C x 120 h, the lamellar + network eutectic morphologies were effectively fragmented and spheroidized into granular + irregular morphologies. The resulting alloy featured excellent mechanical properties with an ultimate compressive strength (UCS) of 1980 +/- 50 MPa, fracture plasticity of similar to 16.6% +/- 1%, and hardness of similar to 448 +/- 15 HV. Compared with the as-cast specimen, the fracture plasticity of the specimen annealed for 120 h increased by 12.7 times, with no UCS reduction. With a further increase in the annealing time, the hard M16Ti6Si7-type silicide was seriously coarsened, deteriorating the alloy's room-temperature mechanical properties but improving its high-temperature ones.

Automated summary

Adopting the idea of thermal modification of conventional Si-containing eutectic alloys, this study aimed to improve the fracture plasticity of the brittle CoFeNi2(Ti3Si5)(0.16) high-entropy alloy by heating it under various annealing conditions. The result showed that the eutectic microstructure transformed from lamellar + network morphologies to granular + irregular morphologies after annealing. The resulting alloy exhibited excellent mechanical properties, including an ultimate compressive strength of 1980 +/- 50 MPa, fracture plasticity of similar to 16.6% +/- 1%, and hardness of similar to 448 +/- 15 HV.