High-strength Co-Al-V-base superalloys strengthened by γ′-Co3(Al,V) with high solvus temperature

The gamma/gamma' 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 gamma'-Co-3(Al, V) phase is provided in this study, and the gamma/gamma' two-phase Co-5Al-14V (at.%) alloy is designed. The gamma'-Co-3(Al,V) phase is proved to be thermodynamically stable at 900 degrees C, and a wide gamma/gamma' two-phase composition region in the Co-Al-V ternary phase diagram at 900 degrees 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 gamma' phase, whereas Cr tends to partition to the gamma matrix. Besides, the gamma/gamma' two-phase Co-30Ni-10Al-5V-4Ta-2Ti (30Ni4Ta2Ti) alloy is designed. The 30Ni4Ta2Ti alloy exhibits a very high gamma' solvus temperature (namely, 1242 +/- 3 degrees 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 degrees C are also close to those of the Mar-M-247 superalloy. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.