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

Highlights: • 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 AlCoCrFeMo_0.05Ni₂ high entropy alloy. • The growth of (Cr, Mo)-rich BCC phase during annealing process resulted in the refinement of (Ni, Al)-rich BCC phase. -- Abstract: Segregation engineering (SE) can optimize the microstructure and improve the properties of traditional alloys. AlCoCrFeNi_2.1 alloy has been declared as a promising superalloy. Mo can improve high temperature performance, AlCoCrFeMo_0.05Ni₂ alloy has been developed. To evaluate the SE in AlCoCrFeMo_0.05Ni₂ 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.