Mechanical Performance and Microstructural Evolution of (NiCo)75Cr17Fe8Cx (x = 0~0.83) Medium Entropy Alloys at Room and Cryogenic Temperatures

Abstract

We investigated the effects of the addition of Co and carbon on the deformation behavior of new medium-entropy alloys (MEAs) designed by increasing the entropy of the conventional NiCrFe-type Alloy 600. The strength/ductility combination of carbon-free (NiCo)75Cr17Fe8 MEA was found to be 729 MPa/81% at 298 K and it increased to a remarkable 1212 MPa/106% at 77 K. The excellent strength and ductility of (NiCo)75Cr17Fe8 at cryogenic temperature is attributed to the increased strain hardening rate caused by the interaction between dislocation slip and deformation twins. Strength/ductility combinations of carbon-doped (NiCo)75Cr17Fe8C0.34 and (NiCo)75Cr17Fe8C0.83 at cryogenic temperature were observed to be 1321 MPa/96% and 1398 MPa/66%, respectively, both of which are superior to those of other high-entropy alloys (HEAs). Strength/ductility combinations of (NiCo)75Cr17Fe8C0.34 and (NiCo)75Cr17Fe8C0.83 at room temperature were found to be 831 MPa/72% and 942 MPa/55%, respectively and both are far superior to 676 MPa/41% of the commercial Alloy 600. Yield strengths of carbon-free and carbon-doped alloys comprised strengthening components from the friction stress, grain size strengthening, carbide strengthening and interstitial strengthening and excellent agreement between the predictions and the experiments was obtained. A design strategy to develop new MEAs by increasing the entropy of the conventional alloys was found to be effective in enhancing the mechanical performance.

The Effects of Annealing at Different Temperatures on Microstructure and Mechanical Properties of Cold-Rolled Al0.3CoCrFeNi High-Entropy Alloy

“…Work hardening and refining hardening can be employed to increase the yield strength of HEA alloys [10,11]. Moreover, alloying is also an effective method to increase the yield stress by solid solution hardening or precipitation hardening [12][13][14][15][16]. The FCC Al 0.3 CoCrFeNi is the most widely studied precipitation hardening HEA alloy [16][17][18][19][20].…”

Corrosion Behavior of AlFeCrCoNiZrx High-Entropy Alloys in 0.5 M Sulfuric Acid Solution

“…% [1][2][3][4]. Many researchers have contributed their efforts to understanding the fabrication, composition, microstructure, and properties of more than 400 HEAs to date [5][6][7][8][9][10][11][12], where the CoCrFeNi system HEAs have been heavily researched, and many studies in the literature have focused on improving the corrosion resistance of CoCrFeNi system HEAs through the addition of other alloy elements, such as Al, Mn, Mo, Cu, and Ti [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Kao et al [14] investigated the electrochemical passive properties of AlxCoCrFeNi alloys by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and weight loss tests, indicating that a higher amount of Al in AlxCoCrFeNi alloys was harmful to the corrosion resistance in a 0. solution, and the pitting potentials of Al0.5CrFe1.5MnNi0.5 HEAs were significantly lower than those of Al-free CrFe1.5MnNi0.5 HEAs in a 1 M NaCl solution [15].…”