Segregation engineering in a promising heat-resistant AlCoCrFeMo0.05Ni2 high entropy alloy

Segregation engineering (SE) can optimize the microstructure and improve the properties of traditional alloys. AlCoCrFeNi2.1 alloy has been declared as a promising superalloy. Mo can improve high temperature performance, AlCoCrFeMo0.05Ni2 alloy has been developed. To evaluate the SE in AlCoCrFeMo0.05Ni2 HEA, annealing process of the alloy was investigated. The experimental results showed that a large number of metastable phases were formed at the lattice defects in the as-cast alloy during annealing. And the main phase of the alloy annealed at 800 °C for 72 h changed from FCC to BCC structures. Moreover, a large number of dislocations and stacking faults were formed in the (Ni, Al)-rich BCC new phase, and finally turned into nanocrystals or twins. At the same time, the (Cr, Mo)-rich BCC phase changed from spherical to rod, square and dish-like during the annealing. The growth of the (Cr, Mo)-rich BCC phase and the mutual restriction of different phases resulted in the refinement of the (Ni, Al)-rich BCC phase during annealing. The high temperature ductility of the alloy has been improved significantly. At 700 °C, its elongation reached 80%, while the strength had still up to 500 MPa. [Display omitted] •A large number of dislocations and stacking faults were discovered in a new metastable (Ni, Al)-rich BCC phase.•Annealing twin transformed from the metastable phase has been found in an as-cast AlCoCrFeMo0.05Ni2 high entropy alloy.•The growth of (Cr, Mo)-rich BCC phase during annealing process resulted in the refinement of (Ni, Al)-rich BCC phase.