Abstract
The synthesis of lightweight yet strong-ductile materials has been an imperative challenge in alloy design. In this study, the CoCrNi-based medium-entropy alloys (MEAs) with added Al and Si were manufactured by vacuum arc melting furnace subsequently followed by cool rolling and anneal process. The mechanical responses of CoCrNiAl0.1Si0.1 MEAs under quasi-static (1 × 10−3 s−1) tensile strength showed that MEAs had an outstanding balance of yield strength, ultimate tensile strength, and elongation. The yield strength, ultimate tensile strength, and elongation were increased from 480 MPa, 900 MPa, and 58% at 298 K to 700 MPa, 1250 MPa, and 72% at 77 K, respectively. Temperature dependencies of the yield strength and strain hardening were investigated to understand the excellent mechanical performance, considering the contribution of lattice distortions, deformation twins, and microbands. Severe lattice distortions were determined to play a predominant role in the temperature-dependent yield stress. The Peierls barrier height increased with decreasing temperature, owing to thermal vibrations causing the effective width of a dislocation core to decrease. Through the thermodynamic formula, the stacking fault energies were calculated to be 14.12 mJ/m2 and 8.32 mJ/m2 at 298 K and 77 K, respectively. In conclusion, the enhanced strength and ductility at cryogenic temperature can be attributed to multiple deformation mechanisms including dislocations, extensive deformation twins, and microbands. The synergistic effect of multiple deformation mechanisms lead to the outstanding mechanical properties of the alloy at room and cryogenic temperature.
Highlights
The previous studies primarily focused on the microstructure evolution of dislocation structure, stacking fault (SF), and deformation twinning to explain the superior strain hardening and significant ultimate tensile strength owing to the mechanical property and deformation mechanisms of High-entropy alloys (HEAs) being strongly dependent on the temperature and microstructure [6,7,13,14]
These studies provide extensive evidence that deformation twinning contributes to the improvement of strength and plasticity simultaneously when the M-HEAs deformed at 77 K and suggested that the index stacking fault energies (SFEs) will drop when the temperature decreases, which is favorable for dislocation glide to the formation of twins and even inducing the martensite phase transformation
The map in showed that the alloy is a completely recrystallized microstructure map in Figure 1b of medium-entropy alloys (MEAs) showed that the alloy is a completely recrystallized microstructure with random random orientation orientation and and multiple multiple micron micron annealing annealing twins twins
Summary
The previous studies primarily focused on the microstructure evolution of dislocation structure, stacking fault (SF), and deformation twinning to explain the superior strain hardening and significant ultimate tensile strength owing to the mechanical property and deformation mechanisms of HEAs being strongly dependent on the temperature and microstructure [6,7,13,14] These studies provide extensive evidence that deformation twinning contributes to the improvement of strength and plasticity simultaneously when the M-HEAs deformed at 77 K and suggested that the index SFEs will drop when the temperature decreases, which is favorable for dislocation glide to the formation of twins and even inducing the martensite phase transformation. It is significant to explain the deformation behavior of CoCrNi-based MEAs containing trace elements at low temperatures, widening their industrial applications in extreme conditions
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