Improved Strength–Ductility Synergy of a CoCrNi Medium‐Entropy Alloy by Ex Situ TiN Nanoparticles

Abstract

The introduction of ex situ reinforcement particles to increase the strength of alloys generally reduces ductility. Herein, a method to fabricate CoCrNi/TiN composite via spark plasma sintering (SPS) and rolling and annealing to achieve a superior combination of strength and ductility is presented. Under the as‐SPSed condition, the CoCrNi/TiN composites exhibit the fracture strain of 41.9%, yield strength (YS) of 0.48 GPa, ultimate tensile strength (UTS) of 0.88 GPa, and hardness of 232.0 Hv. After rolling at 25 °C for the thickness reduction of 50%, the alloy presents fracture strain of 6.9%, YS of 1.24 GPa, UTS of 1.41 GPa, and hardness (408.9 Hv). After rolling at 25 °C for the thickness reduction of 50%, and annealing at 700 °C for 1 h, a good combination of YS of 0.77 GPa, UTS of 1.01 GPa, and fractured strain of 55.2% can be obtained in the samples. The superior strength–ductility synergy can be attributed to the refined structure, the formation of lattices defects (i.e., stacking faults [SFs] and Lomer–Cottrell Locks (LCs)), the interaction of nanotwin–TiN particles, and the concurrent process of potential grain boundary sliding accommodated by intragranular dislocation in the softer face‐centered cubic (fcc) matrix.

Microstructure Characterization and Robust Lubrication Performance of CoCrNi Medium Entropy Alloy with Advanced Electrochemical Boronizing Treatment

“…The concept of medium-entropy alloys (MEAs) is based on highentropy alloys (HEAs), [1][2][3] which are alloys containing three to four elements with equal or nearly equal molar ratios. [4][5][6] In recent years, the face-centered cubic (FCC) CoCrNi MEA has been widely studied due to its impressive mechanical properties, including an excellent combination of strength and ductility, high work hardenability, and fracture toughness. [7][8][9][10][11][12] At room temperature (293 K), CoCrNi has been reported to have an ultimate tensile strength (UTS) of about 1 GPa and uniform elongation of 65%, [13] making it a promising candidate for aviation and aerospace fields.…”