Precipitation behaviors of the rapidly-solidified CoCrFeNiTi high-entropy alloy during aging treatment

Abstract

The precipitation behavior of second phases plays a crucial role in optimizing the microstructure and improving the mechanical properties of precipitation-strengthened high-entropy alloys (HEAs).In this work, the CoCrFeNiTi HEA alloy was fabricated by the laser cladding, and a novel method was proposed to regulate the type, size, and distribution of precipitates in rapidly-solidified CoCrFeNiTi HEA. During the rapid non-equilibrium solidification of laser cladding, the CoCrFeNiTi HEA consisted of FCC phase, Laves phase, and tiny amount of η phase. The 900 ℃ isothermal aging treatment was designed to achieve a fine-distributed η phase with nanometer size. Four types of coherent η phase with different formation mechanisms and morphologies were found. By comparing the aging treatment of 700 ℃ and 1100 ℃, it was revealed that the competition between the continuous precipitation and the discontinuous precipitation played a crucial role in regulating the type and size of the η phase. Low temperature aging facilitated the continuous precipitation of η phases, while high temperature aging favored the discontinuous precipitation. With the 900 ℃ aging, the synergistic relationship between the matrix and the precipitates was optimized. The microhardness and nanohardness of the HEA coating were ∼865 HV and ∼11.2 GPa, respectively, indicating excellent wear resistance capability. This research not only provides insights into the precipitation behavior in rapidly-solidified HEAs but also offers valuable guidelines for designing precipitation-strengthened HEAs with optimized microstructures and superior mechanical properties.