Microstructure and tensile properties of Y2O3-dispersion strengthened CoCrFeNi high entropy alloys prepared via mechanical alloying using pre-alloyed powder

Abstract

Nano-Y₂O₃-dispersion strengthened CoCrFeNi high entropy alloys are fabricated via mechanical alloying and spark plasma sintering using high purity elemental powders or pre-alloyed CoCrFeNi powder. All the alloys show an FCC matrix incorporated by small amount of BCC Cr-rich segregations, whose brittle nature is detrimental to the mechanical properties of the alloys. It has been found that using pre-alloyed powder significantly suppresses the formation of the Cr-rich phase, and its size and volume fraction can be further reduced by increasing the rotation speed of ball-milling during mechanical alloying. Besides, the grain refinement is also achieved under a higher rotation speed. Y₂O₃ nanoparticles with a number density of 1.8 × 10²² m⁻³ and an average diameter of 11.0 ± 7.3 nm are uniformly distributed in the alloy that produced from pre-alloyed powder under the rotation speed of 350 rpm during ball-milling. These Y₂O₃ nanoparticles share coherent interface with the FCC matrix, indicating the in-situ precipitation mechanism. Due to a good combination of grain boundary strengthening, dislocation strengthening and precipitation strengthening, this ODS high entropy alloy possesses a yield strength of 1281 MPa at room temperature.