Kandula Muni Kumar*, MP Singh, SK Makineni, K Chattopadhyay

           Department of Materials Engineering, IISc, Bangalore, India

           *kandulakumar@iisc.ac.in

The studies are conducted to understand the effect of Re addition on coarsening behavior and microstructural evolution of new low-density Co-Ni-Al-Ti-Nb-Cr based superalloy. Lattice misfit is reduced with addition of Re and this depicts a sign reversal from positive to negative misfit which is confirmed from high-resolution XRD. Additionally, the morphological transition from cuboidal to rounded cornered cubes with Re addition is observed. The coarsening studies at 900C, reveals that  precipitate size has significantly reduced and microstructural stability is enhanced as a result of Re addition.

A comprehensive investigation in understanding the coarsening behavior, utilizing the phenomenological perspective way within the theoretical limitations are employed. The interpretations are arrived at by correlating the experimentally obtained parameters such as rate constant, precipitate size distribution (PSD) and standard deviations. The elastic anisotropy is minimized with addition of Re, confirmed from the defects in topological alignment of  and directional coarsening [1]. From theoretical approximations the interfacial parameters were estimated and are presented. However, the variation of / interface width as a function of Re and coarsening time is evaluated from compositional profiles obtained from atom probe tomography (APT). The estimated coarsening rate constants (K) are 1.3, 0.9 and 0.78 (nm3/s) and the / interfacial energies () are 0.94, 0.67 and 0.64 mJ/m2 for 0, 2 and 3 at. % Re additions, respectively. The K and  values for this class of alloys are comparable and better than many existing superalloys [2]. The reduction in interfacial energy, lattice misfit and diffusional kinetics with Re addition can effectively lower the coarsening rates and improves the microstructural stability.

References

[1] M. Degeiter et al.; Acta Materialia, 2020, 187, 41-50.

[2] X. Li et al.; Metallurgical and Materials Transactions A, 2002, 33A, 3367