Development of low-density γ/γ′ Co-Al-Ta-based superalloys with high solvus temperature

The present paper reports the development of W-, Mo-, and V-free and Ni- and Cr-containing Co-Al-Ta-based superalloys. In particular, the presence of a metastable L1(2)-gamma' phase is experimentally verified in Co-12Al-2Ta alloy. The results show that the gamma phase stability is improved and the gamma/gamma' composition range is broadened by rising the Ni content in alloys under study. Moreover, elemental partitioning proves that Cr was a gamma-phase former, which addition reduces the gamma/gamma' lattice misfit and the y precipitate coarsening rate. Moreover, the developed Cr-containing alloys exhibit excellent gamma phase stability even at high temperatures of 800-1100 degrees C. In particular, Co-30Ni-12Al-4Ta-12Cr (12Cr) alloy possesses a good combination of high solvus temperature (similar to 1152 degrees C), low density (similar to 8.38 g/cm(3)), low gamma/gamma' lattice misfit (similar to+0.33%), and low coarsening rate of gamma' precipitate (similar to 1.95 x 10(27) m/s at 900 degrees C). Besides, nominal and specific yield strength values of the developed 12Cr alloy at ambient and high temperatures are no worse than those of other available Cr-containing and W-free cobalt-based superalloys. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.