Faculty Publications
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Item Role of δ-phase on recrystallisation behaviour of Inconel 718(SAGE Publications Inc., 2024) Padasale, B.; Potphode, L.; Dsilva, P.C.; Hegde, S.R.The present work investigates the annealing behaviour of prior-coldworked Inconel 718 (IN718) sheets over wide reduction and temperature ranges by performing cold-rolling and isothermal annealing, followed by mechanical testing and structural characterisation. The study reveals that, with increasing annealing temperature, the prior-coldworked alloy shows non-monotonic M-Type variation with double peak-hardening at 0.3Tm and 0.6Tm. The study discovers that the first peak is due to the ‘static–strain–aging phenomenon’ that precedes recovery-softening. The second peak-hardening is due to precipitation-hardening, following which, the alloy softens due to recrystallisation. Supported by SEM, electron back-scattered diffraction and X-Ray diffraction results, the investigation suggests that the precipitation of fine rod-shaped δ-phase creates numerous nucleation sites at the shear bands that cause recrystallisation-burst at 0.75Tm. However, above 0.75Tm absence of the δ-phase activates grain-boundary migration resulting in rapid grain-coarsening. © The Author(s) 2024.Item Annealing Behavior of Cold-Rolled Inconel 601(Springer, 2024) Dsilva, P.C.; Padasale, B.; Vasavada, J.; Mishra, S.; Hegde, S.R.Present study investigates isothermal annealing behavior of prior cold-worked Inconel 601 (aka, IN 601) sheets. The study comprehensively covers the annealing response of the material over wide cold-reduction and temperature ranges. Using structural characterization and mechanical testing, the study tracks strain-hardening, strain-aging, recovery, and recrystallization stages of IN 601 sheets as a function of degree of cold-reduction and annealing temperature. Using X-Ray diffraction analysis, hardness measurements, and tensile tests, the study reveals that prior cold-worked IN 601, irrespective of the degree of cold-reduction, consistently exhibits strain-aging during low-temperature (~ 0.4Tm) annealing. The investigation establishes that the ‘recovery stage’ is preceded by ‘strain-aging-stage’ during which the alloy exhibits superior strength and hardness than the strain-hardened and recovered states. Based on the thermomechanical experimental results, the current work proposes a recrystallization map that integrates the ‘strain-hardening’ and ‘strain-aging’ stages with the recovery and recrystallization stages. Additionally, microstructural analysis and SEM-EBSD analysis presented in this work indicate that, by suitably controlling strain-hardening and the recrystallization annealing, a refined microstructure comprising high aspect-ratio grains having high-angle grain-boundaries can be obtained that may improve both fatigue and creep properties of IN 601 sheets. © ASM International 2023.Item Influence of ?-Phase on the Grain Shape and Mechanical Properties of Inconel 718(Springer, 2025) Padasale, B.; Hegde, S.R.The present work comparatively studies the thermomechanical processing of mill-annealed, aged, and solution-treated IN718 strips to study the influence of ?-phase precipitates on the grain aspect ratio and the mechanical properties. Prior-treated strips were subjected to thermomechanical processing by cold rolling followed by recrystallization annealing. The processed strips were then mechanically tested and characterized by: hardness measurement, tensile testing, microstructural analysis, electron backscatter diffraction (EBSD) analysis, and x-ray diffraction (XRD) analysis. The results suggest that the recrystallized strips do not show any crystallographic texture, yet possess orthotropic properties along the rolling and transverse directions. The microstructural features correlate well with the mechanical properties, suggesting that the precipitates of ?-phase positively influence the recrystallization kinetics and grain refinement. However, the presence of large fraction of coarse ?-phase precipitates adversely influence the grain aspect ratio and the tensile properties. The study reveals that solution-treated IN718, when subjected to suitable thermomechanical processing, yields a highly refined microstructure with high aspect ratio and superior mechanical properties, especially in the rolling direction. © ASM International 2025.