A L12 precipitation strengthened Co-free medium-entropy alloy with superior high-temperature performance

In present work, the superior high-temperature properties in a novel (Ni, Cr, Fe)3(Al, Ti, Cr)-γʹ (L12) type precipitation-strengthened Co-free medium-entropy alloy (MEA) was systematically evaluated. Experimental results indicate that this γʹ-strengthened alloy demonstrates excellent structure thermal stability and no other brittle intermetallic phases formed at grain boundaries or grain interior during long-term thermal exposures. The γʹ phase in this Co-free MEA exhibits an extraordinary sluggish coarsening rate, which is much lower than most conventional superalloys and recently developing γʹ-strengthened high/medium-entropy alloys (HEAs/MEAs). This γʹ-strengthened alloy also exhibits a good combination of high γʹ-solvus temperature (1068 °C) and low mass density (7.79 g/cm3). More significantly, this γʹ-strengthened MEA shows excellent high-temperature tensile strength, especially outstanding specific strength, which is superior to most Ni/Co-based superalloys. Our present work provides a useful illustration for designing advanced high-temperature alloys based on γʹ(L12)-strengthened HEAs/MEAs, rather than Ni-based/Co-based superalloys.