High-strength Co–Al–V-base superalloys strengthened by γ′-Co ₃ (Al,V) with high solvus temperature

The γ/γ′ two-phase Co–Al–V-base superalloys are investigated in detail, including their phase equilibria, alloying effects, and alloy design. The experimental proof of the existence of a ternary compound with an L1 ₂ -ordered γ′-Co ₃ (Al, V) phase is provided in this study, and the γ/γ′ two-phase Co–5Al–14V (at.%) alloy is designed. The γ′-Co ₃ (Al,V) phase is proved to be thermodynamically stable at 900 °C, and a wide γ/γ′ two-phase composition region in the Co–Al–V ternary phase diagram at 900 °C is identified. The performed investigation of Co–5Al–14V-2X (X: Ti, Cr, Nb, Mo, Ta, and W) and Co-xNi-8Al–12V (x = 10, 20, and 30) quaternary alloys revealed that Ti, Nb, Mo, Ta, W, and Ni tend to concentrate in the γ′ phase, whereas Cr tends to partition to the γ matrix. Besides, the γ/γ′ two-phase Co–30Ni–10Al–5V–4Ta–2Ti (30Ni4Ta2Ti) alloy is designed. The 30Ni4Ta2Ti alloy exhibits a very high γ′ solvus temperature (namely, 1242 ± 3 °C) combined with a low density (8.46 ± 0.08 g cm ⁻³ ), which characteristics are comparable with those of the Mar-M-247 Ni-base superalloy. Moreover, the nominal and the specific yield strength values of the obtained 30Ni4Ta2Ti alloy within the temperature range from 600 to 900 °C are also close to those of the Mar-M-247 superalloy.