Influence of zirconium addition on the microstructure, thermodynamic stability, thermal stability and mechanical properties of mechanical alloyed spark plasma sintered (MA-SPS) FeCoCrNi high entropy alloy

Equiatomic FeCoCrNi (Zr-0) and non-equiatomic FeCoCrNiZr0.4 (Zr-0.4) high-entropy alloys (HEAs) were synthesised by mechanical alloying and spark plasma sintering. XRD analysis verified the formation of FCC and BCC solid solution phases in both alloys after 30 h of ball milling. While the SPS FeCoCrNi alloy contains both FCC and BCC solid solution phases, the FeCoCrNiZr0.4 presents an FCC solid solution. The thermodynamic analysis showed that FeCoCrNiZr0.4 is more stable with respect to the FeCoCrNi alloy. The phase stability of FeCoCrNiZr0.4 was revealed up to similar to 800 degrees C. The shear strength and hardness of the FeCoCrNi HEA improved with Zr addition. Failure analysis of the shear punch tested samples revealed a ductile fracture with dimple structure for FeCoCrNi and a brittle fracture with a smooth featureless surface for FeCoCrNiZr0.4.