Degradation of tensile mechanical properties of two AlxCoCrFeNi (x=0.3 and 0.4) high-entropy alloys exposed to liquid lead-bismuth eutectic at 350 and 500°C

Tensile mechanical properties of two AlxCoCrFeNi (x = 0.3 and 0.4) high-entropy alloys (HEAs) have been tested in liquid lead-bismuth eutectic (LBE) at 350 and 500 °C. The results show that LBE has a mild effect on the mechanical properties of Al0.3CoCrFeNi HEA which is a pure FCC structure, but some traces of liquid metal embrittlement (LME), such as cleavage, are detected at 350 °C and a tendency of intergranular (IG) cracking at 500 °C is also discovered. The mechanical properties of Al0.4CoCrFeNi HEA are strongly temperature-dependent. At 350 °C, the degradation effect of LBE is weak, while after the testing temperature increases to 500 °C, the mechanical properties are severely deteriorated even without the help of LBE. The mechanism responsible for this severe degradation phenomenon can be attributed to a network of thin (Ni, Al)-rich precipitates existing at the grain boundaries of the Al0.4CoCrFeNi HEA. As temperature increases, the precipitate/matrix interphase boundaries (IBs) become weak and can be perfectly wetted by LBE, leading to prevalent IG cracking facets on the fracture surface.