Fig. 1. X-ray diffraction patterns of CoCrFeNi alloy (a) and those doped with 4 at.% Al (b), Mo (c), and Ti (d) annealed at 800, 900, 1000 and 1100 °C for 1 hour following room temperature rolling.

Fig. 2. Back-scattered electron image of CoCrFeNi alloy (a) and those doped with 4 at.% Al (b), Mo (c), and Ti (d) annealed at 800, 900, 1000 and 1100 °C for 1 hour following room temperature rolling.

Fig. 3. TEM micrographs of the Co24Cr24Fe24Ni24Al4 (a), Co24Cr24Fe24Ni24Mo4 (b), and Co24Cr24Fe24Ni24Ti4 alloys (c); the insets in (b) and (c) present the SAED patterns of the corresponding observable particles; (d) HRTEM image of the particle present in the Co24Cr24Fe24Ni24Ti4 alloy.

Fig. 4. Representative engineering stress-strain curves of the CoCrFeNi alloy (a) and those doped with 4 at.% Al (b), Mo (c), and Ti (d) annealed at 800, 900, 1000 and 1100 °C for 1 hour following room temperature rolling.

Fig. 5. Hall-Petch plots showing the effects of grain size, d, on the yield strength, ${{\sigma }_{Y}}$, for the CoCrFeNi alloy and those doped with 4 at.% Al, Mo and Ti; the black and green open circles respectively indicate the 800 °C-and 900 °C-annealed Co24Cr24Fe24Ni24Mo4 and Co24Cr24Fe24Ni24Ti4 alloys; the closed squares correspond to those with additional annealing.

Fig. 6. Relationships of (a) ${{\sigma }_{ss}}\sim {{\varepsilon }_{f}}$ and (b) ${{\sigma }_{ss}}\sim {{\varepsilon }_{l}}$, in which ${{\sigma }_{ss}}$ values are cited from Table 1. ${{\varepsilon }_{f}}$ and ${{\varepsilon }_{l}}$ represent the overall contributions from elastic misfit and were calculated using the atomic size misfit (${{\varepsilon }_{a}}$) and modulus mismatch (${{\varepsilon }_{G}}$).

Fig. 7. Predicted vs. experimental yield strength due to “dilute” doping of the CoCrFeNi alloy; the prediction was made using Eq. (1) by applying the dimensionless parameter f obtained from the linear relation in Fig. 5b to Eq. (3) and assuming a linear relation between kHP and doping concentration;.

Fig. 8. Comparisons of the spin density distribution in one [110] plane in the stacking fault energy calculations based on the slab model. (a) shows the computational model, in which the red atom denotes the dopant element X, (b)-(d) shows the spin density distribution for Al, Ti, and Mo, respectively. The location of the dopants is indicated by the red arrow. The lower panels shows the spin density difference before and after the introduction of stacking fault. Charge accumulation is represented by red while depletion by green. An isovalue of 0.004 e/Å3 was used.

Fig. 9. Stacking fauly energies (SFEs), annealing twin densities (ρtwin) and kHP values of the CoCrFeNi, Co24Cr24Fe24Ni24Al4, Co24Cr24Fe24Ni24Mo4, and Co24Cr24Fe24Ni24Ti4 alloys. Noted first that the ρtwin was defined here as the number of twin boundary intercepts per unit length and second that the for the measurement of ρtwin, the 1000 °C (1 h)-annealed alloys were used since they exhibited similar grain sizes (36-42 μm) and ρtwin was found influenced by the grain size.