Microstructure and Mechanical Properties of CoCrFeNi(TiAl) High Entropy Alloys

Abstract

The structure and mechanical properties of CoCrFeNi and CoCrFeNiTi0.5Al0.5 (in molar ratio) high entropy alloys were investigated using X-ray diffraction (XRD), optical microscope (OM), scanning electron microscope (SEM), hardness and compression tests. With the addition of Ti and Al, the crystal structure of CoCrFeNi changed from FCC to a mixture of FCC and double BCC structures. The lattice parameter of FCC increases upon addition of Al and Ti. The microstructure analysis shows the morphological transition of dendrites from non-equiaxed to equiaxed during the suction casting of CoCrFeNiTi 0.5Al 0.5 alloy. The Vickers microhardness testing of CoCr-FeNi alloy reveals significant increase in hardness with the addition of Al and Ti. The hardness values are improved in as-suction cast CoCrFeNi and CoCrFeNiTi0.5Al 0.5 alloys compared to their ascast alloys due to strengthening. The CoCrFeNiTi0.5Al 0.5 alloy yields at 1997 MPa and fails at 2344 MPa. The fracture mechanism of CoCrFeNiTi 0.5Al 0.5 alloy reveals a cleavage mode.