Analysing the serrated flow in a multi-component Co-base superalloy

Abhinav Kumar Karnati¹, N.T.B.N. Koundinya¹, Anuradha Naik Majila², Chandru Fernando D² and Ravi Sankar Kottada¹*

¹Metallurgical and materials engineering, IIT Madras, Chennai – 600036, India

²Materials Group, GTRE, DRDO, Bengaluru, 560093, India

*Corresponding author: ravi.sankar@iitm.ac.in

Interesting observations in the recent past in multicomponent Co-base alloys have triggered attention in high-temperature Co-base alloys. Among them, the wrought FCC stabilised Co-base multi-component alloys are specifically interesting due to higher melting point, solid solution, and precipitation forming ability[1]. Therefore, understanding the deformation behaviour of these alloys over a wide range of temperatures and strain rates is essential. However, in the quasi-static regime, a few studies have shown that inherent low stacking fault energy leads to a contrasting mechanical behaviour in solid solution Co-base superalloys as compared to the wrought Ni-base superalloys [2,3]. Notedly, these alloys have shown dynamic strain aging (DSA) in quasi-static regime in a certain temperature range. However, there is an equivocal understanding of the rate-controlling solute and the influence of substructure on DSA. Thus, the present study aims to address the origin of DSA in multi-component Co-base superalloy, Co-22Cr-22Ni-14W-2Fe-0.1C.

To establish the DSA regime, tensile tests were carried out at a constant crosshead velocity in the strain rate range of 10^-4 to 10^-1 s^-1 and in the temperature range of room temperature (RT) to 1000°C (Fig. 1). Strain rate sensitivity was measured from the strain rate jump tests in the DSA regime to delineate the Portevin- Le Chatelier (PLC) regime. Comprehensive transmission electron microscopic studies have shown the stacking faults, array of dislocation dipoles and multipoles on (111) planes. Besides, theoretical models were used in estimating the activation energies and drift velocities associated with solute atoms across tested regime[4]. By correlating the present results with existing DSA models, the complex mechanisms responsible for DSA in the present Co-base superalloy are discussed.

References

[1] S. Wei, D.P. Moriarty, M. Xu, J.M. LeBeau, C.C. Tasan, Acta Mater.,2023, 242, 1–13.

[2] H.M. Tawancy, V.R. Ishwar, B.E. Lewis, J. Mater. Sci. Lett.,1986, 5, 337–341.

[3] R. Pal Singh, R.D. Doherty, Metall. Trans. A , 1992, 23, 321–334.

[4] J.P. Hirth, J. Lothe, Theory of Dislocations, 2nd editin, Krieger Publication, 1992.