Abstract
The concept of high-entropy alloy has received lots of attention and research since 2004. Air Force Research Laboratory first reported refractory high-entropy alloy NbTaMoW and VNbTaMoW based on this concept in 2010. VNbTaMoW has high compressive yield strength of 1246 MPa at room temperature and excellent compressive yield strength of 477 MPa at 1600 °C, but has poor room-temperature ductility and much higher density. Afterwards, they reported new refractory high-entropy alloy HfNbTaTiZr with excellent ductility at room temperature and lower density. But, this alloy has poor oxidation resistance and low high-temperature strength. In order to overcome these drawbacks, our laboratory developed new compositions based on HfNbTaTiZr in recent years. From the previous studies in our laboratory, we found the addition of Al and Si in HfNbTaTiZr can effectively enhance high-temperature oxidation resistance and the addition of Mo can improve high-temperature strength. So, refractory high-entropy alloy Al0.5Hf0.5Mo0.5NbTaTiZr is designed in this study. Besides, the addition of Cr and Si to this new alloy will also be studied to see their effects on microstructure, mechanical properties and oxidation resistance. The results show that the addition of Cr can improve the hardness, room-temperature strength but reduce room-temperature ductility and oxidation resistance. On the other hand, the addition of Si improves not only the hardness, room-temperature strength but also high-temperature strength and oxidation resistance without sacrificing the room-temperature ductility. On the whole, (Al0.5Hf0.5Mo0.5NbTaTiZr)97Si3 has the best room- and high-temperature strength, i.e. 1633 MPa at RT and 375 MPa at 1100 °C, and high-temperature oxidation resistance. In addition, the high-temperature strength of this alloy is similar to that of single-crystal Ni-based superalloy CMSX-4 up to 1100 °C. Therefore, this alloy is very promising in high temperature applications.