Quasi-superplasticity in the AlCoNiV medium entropy alloy with Heusler L21 precipitates

The high-temperature tensile deformation behaviors of the recrystallization annealed Al-7(CoNiV)(93) medium entropy alloy with a duplex hierarchical microstructure of face-centered cubic (fcc) and ordered body-centered cubic L2(1) Heusler-type grains were investigated. The alloy showed a remarkably high tensile strength of & SIM;1.1 GPa and good ductility of & SIM;17% at 923 K due to a good strain hardening capacity of 60 MPa. At 1073 K, the highest fracture elongation of & SIM;270% was displayed at a strain rate of 10(-3) s(-1). The strain rate sensitivity was estimated to be about 0.32, which is typical of alloys that show this quasi-superplastic elongation. The activation energy was also estimated to be & SIM;421 kJ/mol. With deformation at 1073 K at a strain rate of 10(-3) s(-1), the duplex microstructure transformed into a refined triplex fcc-L2(1)-sigma equiaxed microstructure. The development of the triplex equiaxed microstructure resulted from dynamic recrystallization (DRX), which assisted in the maximum superplastic-like elongation of 270%. The inability of the alloy to access true superplasticity was attributed to immense cavitation due to the high amount of the brittle sigma phase, which served as de-cohesion sites for the early fracture of the sample. However, the observed quasi-superplasticity could still be useful in superplastic forming operations.

Automated summary

The high-temperature tensile deformation behaviors and microstructural evolution of the recrystallization annealed Al-7(CoNiV)(93) medium entropy alloy were investigated. The alloy exhibited high tensile strength and ductility, and showed quasi-superplastic-like elongation under certain conditions.