Abstract Scope |
In the present work, we show the feasibility of microstructural control by additions of Ti and Cr to a /′ Co-30Ni-10Al-5Mo-2Nb superalloy. Solutioning at 1300 ℃ followed by aging at 900 ℃ leads to homogenous distribution of L12 ordered cuboidal ′ precipitates in face-centered-cubic (fcc) matrix. Compositional measurements show Al, Mo and Nb partition to ′ that indicates the ′ can be described as (Co,Ni)3(Al,Mo,Nb). An addition of 2 at.% Ti leads to increases in the ′ volume fraction from 56 % to 70 % and solvus temperature from 990 ℃ to 1030 ℃. Ti strongly partitions to ′ with respect to ã matrix. Similarly, an addition of 10 at.% Cr to the base alloy leads to a morphological transition of ′ precipitates from cuboidal to near spherical shape, indicating a direct influence on the /′ lattice misfit. Unlike Ti, Cr partitions to matrix and additionally, Cr influences Mo to partition into matrix. A combined addition of Ti and Cr leads to high ′ volume fraction ~ 76 % and an increase in solvus temperature to 1045C, while maintaining the spherical ′ morphology. These superalloys show 0.2 % proof strength comparable to those of Co-Al-W based superalloys. At 870 C, 10 at.% Cr and 2 at.% Ti added alloys show higher specific 0.2 % proof stress than Co-Al-W based superalloys. The obtained results show the microstructural sensitivity of these Co-based superalloys towards their designing for better performance. |