Strengthening CoCrFeNi High Entropy Alloy by In-Situ Synthesis Grain Ceramic-Reinforced Phase of ZrC

Abstract

To attain in-situ ceramic-reinforced phases by adding C powder, Zr purity metal in face-centered cubic (FCC) type CoCrFeNi high-entropy alloy (HEA), a series of (CoCrFeNi)_100-x(ZrC)_x (x = 0, 2, 4, 6, 8 atomic percent, at. %) high-entropy alloys were synthesized by vacuum arc melting. The phase composition, microstructure, tensile properties were studied in this work. It is found that the alloys possess microstructure of FCC phase, (Zr, Ni)-rich carbides and ZrC phase. The in-situ synthesis ZrC phase is randomly precipitated inside the grains. Multi-component (Zr, Ni)-rich carbides forming eutectic-like microstructure morphology with Ni-poor FCC is generated along the grain boundaries. The volume fraction of precipitated phases increases gradually from 0 to 36.7% with the addition of Zr, C elements. The in-situ ZrC ceramics phase hinders grain boundary migration and significantly reduces grain size in alloys. The yield of alloys increases gradually form 155 MPa to 374 MPa with the increasing of Zr, C. In (CoCrFeNi)₉₄(ZrC)₆ alloy, the alloy exhibited the best balanced mechanical performance, including tensile strength of 573 MPa and strain of 15.9%. The improvement of strength is attributed to the coordination of in-situ grain ceramic-reinforced phase of ZrC strengthening, precipitation strengthening, fine grain strengthening and solid solution strengthening. However, excessive (Zr, Ni)-rich carbides phase and impurity carbides will reduce plasticity.

Keywords: In-situ synthesis, High-entropy alloy, Precipitated ZrC phase, Mechanical properties