Microstructural evolution and effect of heat treatment on the precipitation and mechanical behavior of Al0.7CoCrFeNi alloy

The microstructural features and promising properties exhibited by Al0.7CoCrFeNi have led to extensive studies on the alloy. The current work discusses the microstructural evolution, thermal stability and mechanical behavior of the alloy. CALPHAD studies predicated the alloy to be near eutectic with pro-eutectic BCC and eutectic FCC and BCC/B2. However, experimental studies displayed the FCC phase to evolve from a high-temperature B2. Interfacial energy, chemical inhomogeneity and cooling rate were attributed to play a key role in the microstructural evolution and phase stability. Heat treatment resulted in the dissolution of BCC and the formation of Al-Ni-rich B2 phase. During solidification and heat treatment, Widmanstätten FCC formed and coarsened via superledge mechanism. Further, thermal exposure resulted in lamellar instability and localized globularization of the B2 phase. The heat-treated alloy displayed excellent resistance to thermal softening when compared to the cast alloy. Further, the thermally exposed alloy exhibited a superior work hardening rate. [Display omitted] •The study displayed lamellar morphological evolution from a high-temperature B2, contradicting the CALPHAD predictions.•Localized cooling rates during solidification significantly affect the microstructural morphology and residual stresses.•The growth of the lamellar structures was attributed to superledge growth mechanism.•Thermal exposure led to localized globularization and lamellar instability similar to α-β Ti alloys.•Heat-treated alloy showed excellent resistance to thermal softening and superior work hardenability compared to cast alloy.