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Journal Article

Development of new γ′-strengthened Co-based superalloys with low mass density, high solvus temperature and high temperature strength


Makineni,  Surendra Kumar
Atom Probe Tomography, Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Pandey, P., Mukhopadhyay, S., Srivastava, C., Makineni, S. K., & Chattopadhyay, K. (2020). Development of new γ′-strengthened Co-based superalloys with low mass density, high solvus temperature and high temperature strength. Materials Science and Engineering A: Structural Materials Properties Microstructure and Processing, 790: 139578. doi:10.1016/j.msea.2020.139578.

Cite as: https://hdl.handle.net/21.11116/0000-0009-7898-5
In this work we report new gamma' strengthened cobalt base superalloys that have low mass densities in the range of similar to 8.3-8.5 gm/cm(3), high solvus up to similar to 1128 degrees C and high specific 0.2% proof strength of similar to 90 MPa.gm(-1).cm(3) at temperatures up to 770 degrees C. The basic alloy composition is Co-10Al-5Cr-2Ta that exhibits gamma/gamma' microstructure on heat treatment. Electron diffraction and elemental partitioning across gamma/gamma' indicate the y' has an ordered L1(2) structure with a stoichiometry Co-3(Al,Ta,Cr) coherently embedded in disordered face-centered-cubic (fcc) gamma-Co matrix. The gamma' structure is primarily stabilized by Ta addition. The gamma' volume fraction and the solvus temperature of the base alloy was measured to be 14% and 870 degrees C respectively. These values are significantly enhanced by the addition of 30at.% Ni (35% and 975 degrees C) and together with 4at.% Ti attaining the values of 63% and 1128 degrees C, respectively. Atom Probe measurements reveal both Ni and Ti strongly partition to gamma' precipitates enhancing the stability of the gamma' while Cr partitions to the gamma phase. At 900 degrees C after 200 h of aging, the 30at.% Ni added alloy without Ti reveals formation of coarsened gamma' at the grain boundaries, directionally coarsened gamma' with wavy gamma/gamma' interface and coagulated rod shape gamma' inside the grains. Addition of Ti (2 and 4 at. %), however, suppresses the formation of these features up to 1000 h of aging at 900 degrees C. The feasibility of tuning the properties of the present alloys by alloying additions makes them attractive for their further development.