Fig. 1. Calculated Al-Ni-Si phase diagrams in this work along with experimental data [14,[24], [25], [26], [27]]: (a) isothermal section at 550 ℃; (b) isothermal section at 850 ℃; (c) isothermal section at 1000 ℃; (d) vertical section at x(Ni) = 0.1; (e) vertical section at x(Ni) = 0.45; (f) vertical section at x(Ni) = 0.8; (g) liquidus projection.

Fig. 2. Calculated Al-Ni-Y phase diagrams in this work along with experimental data [31,33,36,39]: (a) isothermal section at 500 ℃; (b) isothermal section at 600 ℃; (c) isothermal section at 800 ℃; (d) isothermal section at 1000 ℃; (e) liquidus projection; (f) local magnification in the Al-rich region for the liquidus projection. Chain-like lines in Fig. 2(a)-2(d) highlights the experimental phase equilibria.

Fig. 3. Predicted isothermal sections of the Al-Ni-Si-Y system at 1 wt% Y and (a) 500 ℃; (b) 750 ℃; and (c) 1300 ℃, compared with the experimental results [43]. Three green triangles (#1, #2, and #3) denote the coatings prepared by multi-arc ion plating, the L12 and bcc_B2 phases can always be identified in these coatings at 500 ℃ by XRD; three red circles (#4, #5, and #6) denote the alloys prepared by arc-melting in this work, no bcc_B2 phase appears in alloy #4 while the samples #5 and #6 are calculated to show the coexistence of the L12, bcc_B2, and Ni5Y phases at 750 ℃.

Fig. 4. Predicted non-equilibrium solidification behaviors and equilibrium phase fractions of the NiSiAlY alloys at various mass fractions of Al: (a)(b) #1 Ni-13Al-3Si-1Y; (c)(d) #2 Ni-17Al-3Si-1Y; (e)(f) #3 Ni-21Al-3Si-1Y.

Fig. 5. Predicted non-equilibrium solidification behaviors and equilibrium phase fractions of the NiSiAlY alloys at various mass fractions of Si: (a)(b) #4 Ni-12Al-1Si-1Y; (c)(d) #5 Ni-12Al-3Si-1Y; (e)(f) #6 Ni-12Al-5Si-1Y.

Fig. 6. (a) XRD patterns and BSE images of the NiSiAlY candidates at various contents of Si: (b) #4 Ni-12Al-1Si-1Y; (c) #5 Ni-12Al-3Si-1Y; (d) #6 Ni-12Al-5Si-1Y.Fig. 7 shows the element distribution images of the NiSiAlY candidates at various content of Si (1, 3, and 5 wt.%), where nickel exhibits a dispersive distribution. The detailed atomic ratios for different phases detected in the EDS program are listed in Table 3 as well. Little yttrium is determined in the L12 or bcc_B2 phases, which is consistent with the calculated Al-Ni-Y isothermal sections in Fig. 2(a)-(d). As shown in Fig. 7(c), it is noted that there are two different contrasts for Si in alloy #6, indicating a minor discrepancy of Si in the L12 phase due to the insufficient annealing time.

Fig. 7. Element distribution images of the NiSiAlY candidates at various content of Si: (a) #4 Ni-13Al-3Si-1Y; (b) #5 Ni-17Al-3Si-1Y; (c) #6 Ni-21Al-3Si-1Y.

Fig. 8. Summary of the composition-structure-performance relationships of the NiSiAlY candidates based on the calculated phase diagrams at 750 and 1140 ℃ together with the material design regime. The region highlighted with red dashed lines denotes the compositional range proposed in this work, which may possess a combination of good strength, toughness, high-temperature oxidation, and corrosion resistance simultaneously.