PSI - Issue 71

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

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3x10 -4 s -1 highlighting the transition to superplastic regime (e f >400%). Similar observations are made at 800 °C and 900 °C where the materials tested at 900 °C showing superplastic regime (e f >400%) at all testing conditions.

Fig. 1: Phase map (obtained from EBSD) representing the duplex microstructure after thermo-mechanical processing at 800 ° C 1 hr.

Fig. 2: True stress- elongation (%) curve at different temperatures (a) 700 °C (b) 800 °C (c) 900 °C (Reddy et al., 2024a) at different strain rates. In order to understand the flow behavior strain rate sensitivities are measured from the strain rate jump tests at all three test temperatures. Fig. 3 shows the strain rate jump test at different temperatures of 700 °C to 900 °C. The trend shows that strain rate sensitivity of the materials at all three temperatures is different from each other. Although the strain rate sensitivity reported almost similar values ~0.4 at low strain rates, the strain rate sensitivity reported in 900 °C is in increasing trend (from 0.3 to 0.5) where as it is not significant increase in ‘m’ at lower temperatures particularly at 700 °C. Further correlating the true stress vs. elongation curves (Fig.2 (a)) and strain rate sensitivity curves (Fig.3 (a)) confirms that at higher strain rates the materials show good strength owing to the intragranular dislocation motion predominant deformation mechanism leading to significant dislocation strengthening(Reddy et al., 2017) where as possible superplastic regime with flow softening at lower strain rates. In