Microstructural Evolution and Mechanical Behaviour of Near-Eutectic High Entropy Alloy

In the current work, the thermal stability of the eutectic regions and precipitation and mechanical behaviour of near eutectic high-entropy alloy is studied. The alloy solidified as FCC and underwent sequential ordering to L1(2) with order-disorder transition temperature between 700 & DEG;C and 1000 & DEG;C. Cooling rate, variation in the concentration boundary layer, thermal gradient and interfacial energy were attributed to define the eutectic morphology (L1(2) and B2). Thermal exposure resulted in homogeneous precipitation of acicular Al-Ni-rich B2 phase within the proeutectic and irregular eutectic regions. The preferential B2 precipitation within the irregular eutectic regions was attributed to the lower stability and higher lattice strain associated with these regions. The FCC: B2 phase fraction after heat treatment was similar to that of the eutectic alloy. Furthermore, lamellar degradation, globularization and Ostwald ripening of the B2 phase were observed after heat treatment. Lamellar degradation occurred via mechanisms like cylinderization, edge spheroidization, termination migration and boundary splitting. The experimental observations on the phase evolution, stability and order-disorder transformation matched well with the CALPHAD predictions except for the & sigma; phase formation. B2 precipitation during heat treatment enhanced the mechanical behaviour of the alloy. However, the work hardening rate was superior for as-cast alloy.

Automated summary

This study investigates the thermal stability, precipitation, and mechanical behavior of near eutectic high-entropy alloy. The alloy solidifies as FCC and undergoes sequential ordering to L1(2) with a transition temperature between 700°C and 1000°C. The eutectic morphology (L1(2) and B2) is defined by cooling rate, variation in the concentration boundary layer, thermal gradient, and interfacial energy. Thermal exposure results in homogeneous precipitation of Al-Ni-rich B2 phase within the proeutectic and irregular eutectic regions. B2 precipitation during heat treatment enhances the mechanical behavior of the alloy, but the as-cast alloy has a superior work hardening rate.