Phase transformation of AB5 to AB2 type phase on substitution of Mn with Zr in TiVCoNi (ZrxMn2-x) (x = 0, 0.3, 0.6, 1.0) high entropy alloys

Abstract

In this present investigation, we discussed the synthesis, microstructure, and phase transformation from BCC (AB5) to C14 Laves (AB2) phase in TiVCoNi (ZrxMn2-x) (x = 0, 0.3, 0.6, 1.0) high entropy alloys on substituting Mn with Zr. These high entropy alloys were synthesized using a 35 kW radio frequency induction furnace under argon atmosphere. At x = 0 (i.e in quinary HEA), the single BCC phase is observed, whereas at x = 1 (i.e, in hexanery HEA), the single C14 Laves phase was found to be stable. The calculations of the thermodynamic parameters have been done with the help of Miedema's semi-empirical model and other models available in literature. TiVCoNi (ZrxMn33.32-x) high entropy alloys have exhibited mixing enthalpy corresponding to TiVCoNi (ZrxMn2-x) at x = 0, 0.3, 0.6, 1 as −15.6 kJ/mol, −18.1 kJ/mol, −22.8 kJ/mol, −25.3 kJ/mol respectively. The corresponding atomic radius mismatch was found to be 10.03%, 11.85%, 10.18%, and 9.86%. It is established that on replacing Mn with Zr, the mixture of the BCC and Laves phase was observed, which was converted into a single C14 intermetallic Laves phase at equiatomic composition i.e., x = 1. Further, the study of surface morphology and elemental composition of these as-cast high entropy alloys gives us the idea that hardness increases on substitution of Mn in BCC phased-based TiVCoNi (ZrxMn2-x) (x = 0, 0.3, 0.6, 1.0) high entropy alloys due to the evolution of hard C14 Laves phase.