PSI - Issue 71

S.R. Reddy et al. / Procedia Structural Integrity 71 (2025) 172–179

177

Further phase fractions have not significantly affected with temperature or deformation and is consistent with recrystallization kinetics(Wani T. and Sheikh S. and Bhattacharjee P.P. and Guo S. and Tsuji N., 2016) based studies. Further the grain coarsening as observed at lower strain rates at 900 °C (high temperature) significantly limited the ductility of the material to <600% at lower strain rates of 3x10 -4 s -1 . However, the high strain rate superplasticity of ~960% with a combined effect of GBS and grain growth resistance at 10 -1 s -1 and 900 °C has shown remarkable ductility making this a suitable candidate for superplastic forming for aerospace applications. Although this material shows significant ductility it is inferior in comparison to conventional superplastic materials. This decreased ductility is found to be due to the formation of stringer cavities in these materials with limited growth of these cavities with average size of 1- 5 μm (Reddy et al., 2024b). The test data as shown in Table 1 represents a lower grain size at grip in comparison to fracture section under all conditions confirming the presence of deformation induced grain growth under superplastic conditions. The materials show significantly lowered but appreciable ductility at 900 C under slow strain rate condition and it is mainly attributed to the flow localization, low strain rate sensitivity coupled with the substantial grain growth. This confirms that the present EHEA is very sensitive to grain size to exhibit extraordinary ductility. Over all the AlCoCrFeNi 2.1 EHEA has shown potential to be a suitable candidate for Industrial forming of Aerospace applications. Table .1 Variation of grain size and phase fraction of the material at different test conditions

4. Conclusions AlCoCrFeNi 2.1 HEA revealed high strain rate super plasticity at high temperatures with a high ductility of ~960% at a high strain rate of 10 -1 s -1 . The effect of strain rate ( 3x10 -4 s -1 to 10 -1 s -1 ) and temperature (700 °C to 900 °C) on the deformation behavior of the fine grained EHEA is studied in detail. Both temperature and strain rate has dominant effect on the ductility and the strain rate sensitivity. The activation energy calculated to be ~204 kJ/mole with average stress exponent (n) of ~2.5. The strain rate sensitivity (m) decreased from 0.5 to 0.3 at 900 °C and similar trend is witnessed at different strain rates at lower temperatures. The material exhibited grain boundary sliding with deformation induced grain growth at higher temperatures whereas dynamic recrystallization with intragranular dislocation activity is found to be the dominant deformation mechanism at lower temperatures. 5. Acknowledgements The author acknowledges all the sponsoring agencies including Department of Science and Technology (DST), India and Swedish Research Council for the financial support. The author also acknowledges the support of Prof. P.P. Bhattacharjee (IIT Hyderabad, India), Prof. A.H. Chokshi (IISc Bangalore, India) and Prof. Sheng Guo (Chalmers University, Sweden) for the experimental work. 6. References Ahmed, M. Z., Chadha, K., Reddy, S. R., Shahriari, D., Bhattacharjee, P. P., & Jahazi, M. 2020. Influence of Process